]> git.saurik.com Git - apple/xnu.git/blobdiff - bsd/miscfs/specfs/spec_vnops.c
xnu-6153.41.3.tar.gz
[apple/xnu.git] / bsd / miscfs / specfs / spec_vnops.c
index 52cf1c806285bbf346e18db20a8fe4f3561dc9c1..3008946345d27b5b33d11a136b26c3d42c693bb8 100644 (file)
@@ -1,8 +1,8 @@
 /*
- * Copyright (c) 2000-2006 Apple Computer, Inc. All rights reserved.
+ * Copyright (c) 2000-2019 Apple Computer, Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
- * 
+ *
  * This file contains Original Code and/or Modifications of Original Code
  * as defined in and that are subject to the Apple Public Source License
  * Version 2.0 (the 'License'). You may not use this file except in
  * unlawful or unlicensed copies of an Apple operating system, or to
  * circumvent, violate, or enable the circumvention or violation of, any
  * terms of an Apple operating system software license agreement.
- * 
+ *
  * Please obtain a copy of the License at
  * http://www.opensource.apple.com/apsl/ and read it before using this file.
- * 
+ *
  * The Original Code and all software distributed under the License are
  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
@@ -22,7 +22,7 @@
  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  * Please see the License for the specific language governing rights and
  * limitations under the License.
- * 
+ *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  */
 /* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
 #include <sys/disk.h>
 #include <sys/uio_internal.h>
 #include <sys/resource.h>
+#include <machine/machine_routines.h>
 #include <miscfs/specfs/specdev.h>
 #include <vfs/vfs_support.h>
+#include <vfs/vfs_disk_conditioner.h>
+
 #include <kern/assert.h>
 #include <kern/task.h>
+#include <kern/sched_prim.h>
+#include <kern/thread.h>
+#include <kern/policy_internal.h>
+#include <kern/timer_call.h>
+#include <kern/waitq.h>
+
+#include <pexpert/pexpert.h>
 
 #include <sys/kdebug.h>
+#include <libkern/section_keywords.h>
 
 /* XXX following three prototypes should be in a header file somewhere */
-extern dev_t   chrtoblk(dev_t dev);
-extern int     iskmemdev(dev_t dev);
-extern int     bpfkqfilter(dev_t dev, struct knote *kn);
-extern int     ptsd_kqfilter(dev_t dev, struct knote *kn);
+extern dev_t    chrtoblk(dev_t dev);
+extern boolean_t        iskmemdev(dev_t dev);
+extern int bpfkqfilter(dev_t dev, struct knote *kn);
+extern int ptsd_kqfilter(dev_t, struct knote *);
+extern int ptmx_kqfilter(dev_t, struct knote *);
 
 struct vnode *speclisth[SPECHSZ];
 
 /* symbolic sleep message strings for devices */
-char   devopn[] = "devopn";
-char   devio[] = "devio";
-char   devwait[] = "devwait";
-char   devin[] = "devin";
-char   devout[] = "devout";
-char   devioc[] = "devioc";
-char   devcls[] = "devcls";
+char    devopn[] = "devopn";
+char    devio[] = "devio";
+char    devwait[] = "devwait";
+char    devin[] = "devin";
+char    devout[] = "devout";
+char    devioc[] = "devioc";
+char    devcls[] = "devcls";
 
 #define VOPFUNC int (*)(void *)
 
-int (**spec_vnodeop_p)(void *);
-struct vnodeopv_entry_desc spec_vnodeop_entries[] = {
-       { &vnop_default_desc, (VOPFUNC)vn_default_error },
-       { &vnop_lookup_desc, (VOPFUNC)spec_lookup },            /* lookup */
-       { &vnop_create_desc, (VOPFUNC)err_create },             /* create */
-       { &vnop_mknod_desc, (VOPFUNC)err_mknod },               /* mknod */
-       { &vnop_open_desc, (VOPFUNC)spec_open },                        /* open */
-       { &vnop_close_desc, (VOPFUNC)spec_close },              /* close */
-       { &vnop_access_desc, (VOPFUNC)spec_access },            /* access */
-       { &vnop_getattr_desc, (VOPFUNC)spec_getattr },          /* getattr */
-       { &vnop_setattr_desc, (VOPFUNC)spec_setattr },          /* setattr */
-       { &vnop_read_desc, (VOPFUNC)spec_read },                        /* read */
-       { &vnop_write_desc, (VOPFUNC)spec_write },              /* write */
-       { &vnop_ioctl_desc, (VOPFUNC)spec_ioctl },              /* ioctl */
-       { &vnop_select_desc, (VOPFUNC)spec_select },            /* select */
-       { &vnop_revoke_desc, (VOPFUNC)nop_revoke },             /* revoke */
-       { &vnop_mmap_desc, (VOPFUNC)err_mmap },                 /* mmap */
-       { &vnop_fsync_desc, (VOPFUNC)spec_fsync },              /* fsync */
-       { &vnop_remove_desc, (VOPFUNC)err_remove },             /* remove */
-       { &vnop_link_desc, (VOPFUNC)err_link },                 /* link */
-       { &vnop_rename_desc, (VOPFUNC)err_rename },             /* rename */
-       { &vnop_mkdir_desc, (VOPFUNC)err_mkdir },               /* mkdir */
-       { &vnop_rmdir_desc, (VOPFUNC)err_rmdir },               /* rmdir */
-       { &vnop_symlink_desc, (VOPFUNC)err_symlink },           /* symlink */
-       { &vnop_readdir_desc, (VOPFUNC)err_readdir },           /* readdir */
-       { &vnop_readlink_desc, (VOPFUNC)err_readlink },         /* readlink */
-       { &vnop_inactive_desc, (VOPFUNC)nop_inactive },         /* inactive */
-       { &vnop_reclaim_desc, (VOPFUNC)nop_reclaim },           /* reclaim */
-       { &vnop_strategy_desc, (VOPFUNC)spec_strategy },                /* strategy */
-       { &vnop_pathconf_desc, (VOPFUNC)spec_pathconf },                /* pathconf */
-       { &vnop_advlock_desc, (VOPFUNC)err_advlock },           /* advlock */
-       { &vnop_bwrite_desc, (VOPFUNC)spec_bwrite },            /* bwrite */
-       { &vnop_pagein_desc, (VOPFUNC)err_pagein },             /* Pagein */
-       { &vnop_pageout_desc, (VOPFUNC)err_pageout },           /* Pageout */
-        { &vnop_copyfile_desc, (VOPFUNC)err_copyfile },                /* Copyfile */
-       { &vnop_blktooff_desc, (VOPFUNC)spec_blktooff },                /* blktooff */
-       { &vnop_offtoblk_desc, (VOPFUNC)spec_offtoblk },                /* offtoblk */
-       { &vnop_blockmap_desc, (VOPFUNC)spec_blockmap },                /* blockmap */
-       { (struct vnodeop_desc*)NULL, (int(*)())NULL }
+int(**spec_vnodeop_p)(void *);
+const struct vnodeopv_entry_desc spec_vnodeop_entries[] = {
+       { .opve_op = &vnop_default_desc, .opve_impl = (VOPFUNC)vn_default_error },
+       { .opve_op = &vnop_lookup_desc, .opve_impl = (VOPFUNC)spec_lookup },            /* lookup */
+       { .opve_op = &vnop_create_desc, .opve_impl = (VOPFUNC)err_create },             /* create */
+       { .opve_op = &vnop_mknod_desc, .opve_impl = (VOPFUNC)err_mknod },               /* mknod */
+       { .opve_op = &vnop_open_desc, .opve_impl = (VOPFUNC)spec_open },                        /* open */
+       { .opve_op = &vnop_close_desc, .opve_impl = (VOPFUNC)spec_close },              /* close */
+       { .opve_op = &vnop_access_desc, .opve_impl = (VOPFUNC)spec_access },            /* access */
+       { .opve_op = &vnop_getattr_desc, .opve_impl = (VOPFUNC)spec_getattr },          /* getattr */
+       { .opve_op = &vnop_setattr_desc, .opve_impl = (VOPFUNC)spec_setattr },          /* setattr */
+       { .opve_op = &vnop_read_desc, .opve_impl = (VOPFUNC)spec_read },                        /* read */
+       { .opve_op = &vnop_write_desc, .opve_impl = (VOPFUNC)spec_write },              /* write */
+       { .opve_op = &vnop_ioctl_desc, .opve_impl = (VOPFUNC)spec_ioctl },              /* ioctl */
+       { .opve_op = &vnop_select_desc, .opve_impl = (VOPFUNC)spec_select },            /* select */
+       { .opve_op = &vnop_revoke_desc, .opve_impl = (VOPFUNC)nop_revoke },             /* revoke */
+       { .opve_op = &vnop_mmap_desc, .opve_impl = (VOPFUNC)err_mmap },                 /* mmap */
+       { .opve_op = &vnop_fsync_desc, .opve_impl = (VOPFUNC)spec_fsync },              /* fsync */
+       { .opve_op = &vnop_remove_desc, .opve_impl = (VOPFUNC)err_remove },             /* remove */
+       { .opve_op = &vnop_link_desc, .opve_impl = (VOPFUNC)err_link },                 /* link */
+       { .opve_op = &vnop_rename_desc, .opve_impl = (VOPFUNC)err_rename },             /* rename */
+       { .opve_op = &vnop_mkdir_desc, .opve_impl = (VOPFUNC)err_mkdir },               /* mkdir */
+       { .opve_op = &vnop_rmdir_desc, .opve_impl = (VOPFUNC)err_rmdir },               /* rmdir */
+       { .opve_op = &vnop_symlink_desc, .opve_impl = (VOPFUNC)err_symlink },           /* symlink */
+       { .opve_op = &vnop_readdir_desc, .opve_impl = (VOPFUNC)err_readdir },           /* readdir */
+       { .opve_op = &vnop_readlink_desc, .opve_impl = (VOPFUNC)err_readlink },         /* readlink */
+       { .opve_op = &vnop_inactive_desc, .opve_impl = (VOPFUNC)nop_inactive },         /* inactive */
+       { .opve_op = &vnop_reclaim_desc, .opve_impl = (VOPFUNC)nop_reclaim },           /* reclaim */
+       { .opve_op = &vnop_strategy_desc, .opve_impl = (VOPFUNC)spec_strategy },                /* strategy */
+       { .opve_op = &vnop_pathconf_desc, .opve_impl = (VOPFUNC)spec_pathconf },                /* pathconf */
+       { .opve_op = &vnop_advlock_desc, .opve_impl = (VOPFUNC)err_advlock },           /* advlock */
+       { .opve_op = &vnop_bwrite_desc, .opve_impl = (VOPFUNC)spec_bwrite },            /* bwrite */
+       { .opve_op = &vnop_pagein_desc, .opve_impl = (VOPFUNC)err_pagein },             /* Pagein */
+       { .opve_op = &vnop_pageout_desc, .opve_impl = (VOPFUNC)err_pageout },           /* Pageout */
+       { .opve_op = &vnop_copyfile_desc, .opve_impl = (VOPFUNC)err_copyfile },         /* Copyfile */
+       { .opve_op = &vnop_blktooff_desc, .opve_impl = (VOPFUNC)spec_blktooff },                /* blktooff */
+       { .opve_op = &vnop_offtoblk_desc, .opve_impl = (VOPFUNC)spec_offtoblk },                /* offtoblk */
+       { .opve_op = &vnop_blockmap_desc, .opve_impl = (VOPFUNC)spec_blockmap },                /* blockmap */
+       { .opve_op = (struct vnodeop_desc*)NULL, .opve_impl = (int (*)(void *))NULL }
 };
-struct vnodeopv_desc spec_vnodeop_opv_desc =
-       { &spec_vnodeop_p, spec_vnodeop_entries };
+const struct vnodeopv_desc spec_vnodeop_opv_desc =
+{ .opv_desc_vector_p = &spec_vnodeop_p, .opv_desc_ops = spec_vnodeop_entries };
 
 
 static void set_blocksize(vnode_t, dev_t);
 
+#define LOWPRI_TIER1_WINDOW_MSECS         25
+#define LOWPRI_TIER2_WINDOW_MSECS         100
+#define LOWPRI_TIER3_WINDOW_MSECS         500
+
+#define LOWPRI_TIER1_IO_PERIOD_MSECS      40
+#define LOWPRI_TIER2_IO_PERIOD_MSECS      85
+#define LOWPRI_TIER3_IO_PERIOD_MSECS      200
+
+#define LOWPRI_TIER1_IO_PERIOD_SSD_MSECS  5
+#define LOWPRI_TIER2_IO_PERIOD_SSD_MSECS  15
+#define LOWPRI_TIER3_IO_PERIOD_SSD_MSECS  25
+
+
+int     throttle_windows_msecs[THROTTLE_LEVEL_END + 1] = {
+       0,
+       LOWPRI_TIER1_WINDOW_MSECS,
+       LOWPRI_TIER2_WINDOW_MSECS,
+       LOWPRI_TIER3_WINDOW_MSECS,
+};
+
+int     throttle_io_period_msecs[THROTTLE_LEVEL_END + 1] = {
+       0,
+       LOWPRI_TIER1_IO_PERIOD_MSECS,
+       LOWPRI_TIER2_IO_PERIOD_MSECS,
+       LOWPRI_TIER3_IO_PERIOD_MSECS,
+};
+
+int     throttle_io_period_ssd_msecs[THROTTLE_LEVEL_END + 1] = {
+       0,
+       LOWPRI_TIER1_IO_PERIOD_SSD_MSECS,
+       LOWPRI_TIER2_IO_PERIOD_SSD_MSECS,
+       LOWPRI_TIER3_IO_PERIOD_SSD_MSECS,
+};
+
+
+int     throttled_count[THROTTLE_LEVEL_END + 1];
 
 struct _throttle_io_info_t {
-       struct timeval  last_normal_IO_timestamp;
-       struct timeval  last_IO_timestamp;
-       SInt32 numthreads_throttling;
-       SInt32 refcnt;
-       SInt32 alloc;
+       lck_mtx_t       throttle_lock;
+
+       struct timeval  throttle_last_write_timestamp;
+       struct timeval  throttle_min_timer_deadline;
+       struct timeval  throttle_window_start_timestamp[THROTTLE_LEVEL_END + 1]; /* window starts at both the beginning and completion of an I/O */
+       struct timeval  throttle_last_IO_timestamp[THROTTLE_LEVEL_END + 1];
+       pid_t           throttle_last_IO_pid[THROTTLE_LEVEL_END + 1];
+       struct timeval  throttle_start_IO_period_timestamp[THROTTLE_LEVEL_END + 1];
+       int32_t throttle_inflight_count[THROTTLE_LEVEL_END + 1];
+
+       TAILQ_HEAD(, uthread) throttle_uthlist[THROTTLE_LEVEL_END + 1];         /* Lists of throttled uthreads */
+       int             throttle_next_wake_level;
+
+       thread_call_t   throttle_timer_call;
+       int32_t throttle_timer_ref;
+       int32_t throttle_timer_active;
+
+       int32_t throttle_io_count;
+       int32_t throttle_io_count_begin;
+       int    *throttle_io_periods;
+       uint32_t throttle_io_period_num;
+
+       int32_t throttle_refcnt;
+       int32_t throttle_alloc;
+       int32_t throttle_disabled;
+       int32_t throttle_is_fusion_with_priority;
 };
 
 struct _throttle_io_info_t _throttle_io_info[LOWPRI_MAX_NUM_DEV];
 
-static void throttle_info_update_internal(void *throttle_info, int flags, boolean_t isssd);
+
+int     lowpri_throttle_enabled = 1;
 
 
+static void throttle_info_end_io_internal(struct _throttle_io_info_t *info, int throttle_level);
+static int throttle_info_update_internal(struct _throttle_io_info_t *info, uthread_t ut, int flags, boolean_t isssd, boolean_t inflight, struct bufattr *bap);
+static int throttle_get_thread_throttle_level(uthread_t ut);
+static int throttle_get_thread_throttle_level_internal(uthread_t ut, int io_tier);
+void throttle_info_mount_reset_period(mount_t mp, int isssd);
 
 /*
  * Trivial lookup routine that always fails.
@@ -174,44 +249,43 @@ static void throttle_info_update_internal(void *throttle_info, int flags, boolea
 int
 spec_lookup(struct vnop_lookup_args *ap)
 {
-
        *ap->a_vpp = NULL;
-       return (ENOTDIR);
+       return ENOTDIR;
 }
 
 static void
 set_blocksize(struct vnode *vp, dev_t dev)
 {
-    int (*size)(dev_t);
-    int rsize;
+       int (*size)(dev_t);
+       int rsize;
 
-    if ((major(dev) < nblkdev) && (size = bdevsw[major(dev)].d_psize)) {
-        rsize = (*size)(dev);
-       if (rsize <= 0)        /* did size fail? */
-           vp->v_specsize = DEV_BSIZE;
-       else
-           vp->v_specsize = rsize;
-    }
-    else
-           vp->v_specsize = DEV_BSIZE;
+       if ((major(dev) < nblkdev) && (size = bdevsw[major(dev)].d_psize)) {
+               rsize = (*size)(dev);
+               if (rsize <= 0) { /* did size fail? */
+                       vp->v_specsize = DEV_BSIZE;
+               } else {
+                       vp->v_specsize = rsize;
+               }
+       } else {
+               vp->v_specsize = DEV_BSIZE;
+       }
 }
 
 void
 set_fsblocksize(struct vnode *vp)
 {
-       
        if (vp->v_type == VBLK) {
                dev_t dev = (dev_t)vp->v_rdev;
                int maj = major(dev);
 
-               if ((u_int)maj >= (u_int)nblkdev)
+               if ((u_int)maj >= (u_int)nblkdev) {
                        return;
+               }
 
                vnode_lock(vp);
                set_blocksize(vp, dev);
                vnode_unlock(vp);
        }
-
 }
 
 
@@ -231,40 +305,42 @@ spec_open(struct vnop_open_args *ap)
        /*
         * Don't allow open if fs is mounted -nodev.
         */
-       if (vp->v_mount && (vp->v_mount->mnt_flag & MNT_NODEV))
-               return (ENXIO);
+       if (vp->v_mount && (vp->v_mount->mnt_flag & MNT_NODEV)) {
+               return ENXIO;
+       }
 
        switch (vp->v_type) {
-
        case VCHR:
-               if ((u_int)maj >= (u_int)nchrdev)
-                       return (ENXIO);
+               if ((u_int)maj >= (u_int)nchrdev) {
+                       return ENXIO;
+               }
                if (cred != FSCRED && (ap->a_mode & FWRITE)) {
+#if 0
                        /*
                         * When running in very secure mode, do not allow
                         * opens for writing of any disk character devices.
                         */
-                       if (securelevel >= 2 && isdisk(dev, VCHR))
-                               return (EPERM);
+                       if (securelevel >= 2 && isdisk(dev, VCHR)) {
+                               return EPERM;
+                       }
+#endif
+
+                       /* Never allow writing to /dev/mem or /dev/kmem */
+                       if (iskmemdev(dev)) {
+                               return EPERM;
+                       }
                        /*
-                        * When running in secure mode, do not allow opens
-                        * for writing of /dev/mem, /dev/kmem, or character
-                        * devices whose corresponding block devices are
-                        * currently mounted.
+                        * When running in secure mode, do not allow opens for
+                        * writing of character devices whose corresponding block
+                        * devices are currently mounted.
                         */
                        if (securelevel >= 1) {
-                               if ((bdev = chrtoblk(dev)) != NODEV && check_mountedon(bdev, VBLK, &error))
-                                       return (error);
-                               if (iskmemdev(dev))
-                                       return (EPERM);
+                               if ((bdev = chrtoblk(dev)) != NODEV && check_mountedon(bdev, VBLK, &error)) {
+                                       return error;
+                               }
                        }
                }
-               if (cdevsw[maj].d_type == D_TTY) {
-                       vnode_lock(vp);
-                       vp->v_flag |= VISTTY;
-                       vnode_unlock(vp);
-               }
-               
+
                devsw_lock(dev, S_IFCHR);
                error = (*cdevsw[maj].d_open)(dev, ap->a_mode, S_IFCHR, p);
 
@@ -275,13 +351,13 @@ spec_open(struct vnop_open_args *ap)
                devsw_unlock(dev, S_IFCHR);
 
                if (error == 0 && cdevsw[maj].d_type == D_DISK && !vp->v_un.vu_specinfo->si_initted) {
-                       int     isssd = 0;
+                       int     isssd = 0;
                        uint64_t throttle_mask = 0;
                        uint32_t devbsdunit = 0;
 
                        if (VNOP_IOCTL(vp, DKIOCGETTHROTTLEMASK, (caddr_t)&throttle_mask, 0, NULL) == 0) {
-                       
-                               if (VNOP_IOCTL(vp, DKIOCISSOLIDSTATE, (caddr_t)&isssd, 0, ap->a_context) == 0) {
+                               if (throttle_mask != 0 &&
+                                   VNOP_IOCTL(vp, DKIOCISSOLIDSTATE, (caddr_t)&isssd, 0, ap->a_context) == 0) {
                                        /*
                                         * as a reasonable approximation, only use the lowest bit of the mask
                                         * to generate a disk unit number
@@ -289,7 +365,7 @@ spec_open(struct vnop_open_args *ap)
                                        devbsdunit = num_trailing_0(throttle_mask);
 
                                        vnode_lock(vp);
-                                       
+
                                        vp->v_un.vu_specinfo->si_isssd = isssd;
                                        vp->v_un.vu_specinfo->si_devbsdunit = devbsdunit;
                                        vp->v_un.vu_specinfo->si_throttle_mask = throttle_mask;
@@ -305,24 +381,27 @@ spec_open(struct vnop_open_args *ap)
                                vnode_unlock(vp);
                        }
                }
-               return (error);
+               return error;
 
        case VBLK:
-               if ((u_int)maj >= (u_int)nblkdev)
-                       return (ENXIO);
+               if ((u_int)maj >= (u_int)nblkdev) {
+                       return ENXIO;
+               }
                /*
                 * When running in very secure mode, do not allow
                 * opens for writing of any disk block devices.
                 */
                if (securelevel >= 2 && cred != FSCRED &&
-                   (ap->a_mode & FWRITE) && bdevsw[maj].d_type == D_DISK)
-                       return (EPERM);
+                   (ap->a_mode & FWRITE) && bdevsw[maj].d_type == D_DISK) {
+                       return EPERM;
+               }
                /*
                 * Do not allow opens of block devices that are
                 * currently mounted.
                 */
-               if ( (error = vfs_mountedon(vp)) )
-                       return (error);
+               if ((error = vfs_mountedon(vp))) {
+                       return error;
+               }
 
                devsw_lock(dev, S_IFBLK);
                error = (*bdevsw[maj].d_open)(dev, ap->a_mode, S_IFBLK, p);
@@ -332,47 +411,47 @@ spec_open(struct vnop_open_args *ap)
                devsw_unlock(dev, S_IFBLK);
 
                if (!error) {
-                   u_int64_t blkcnt;
-                   u_int32_t blksize;
+                       u_int64_t blkcnt;
+                       u_int32_t blksize;
                        int setsize = 0;
                        u_int32_t size512 = 512;
 
 
-                   if (!VNOP_IOCTL(vp, DKIOCGETBLOCKSIZE, (caddr_t)&blksize, 0, ap->a_context)) {
+                       if (!VNOP_IOCTL(vp, DKIOCGETBLOCKSIZE, (caddr_t)&blksize, 0, ap->a_context)) {
                                /* Switch to 512 byte sectors (temporarily) */
 
                                if (!VNOP_IOCTL(vp, DKIOCSETBLOCKSIZE, (caddr_t)&size512, FWRITE, ap->a_context)) {
-                               /* Get the number of 512 byte physical blocks. */
-                               if (!VNOP_IOCTL(vp, DKIOCGETBLOCKCOUNT, (caddr_t)&blkcnt, 0, ap->a_context)) {
+                                       /* Get the number of 512 byte physical blocks. */
+                                       if (!VNOP_IOCTL(vp, DKIOCGETBLOCKCOUNT, (caddr_t)&blkcnt, 0, ap->a_context)) {
                                                setsize = 1;
-                               }
+                                       }
                                }
                                /* If it doesn't set back, we can't recover */
-                               if (VNOP_IOCTL(vp, DKIOCSETBLOCKSIZE, (caddr_t)&blksize, FWRITE, ap->a_context))
-                               error = ENXIO;
-                   }
+                               if (VNOP_IOCTL(vp, DKIOCSETBLOCKSIZE, (caddr_t)&blksize, FWRITE, ap->a_context)) {
+                                       error = ENXIO;
+                               }
+                       }
 
 
                        vnode_lock(vp);
-                   set_blocksize(vp, dev);
+                       set_blocksize(vp, dev);
 
-                   /*
-                    * Cache the size in bytes of the block device for later
-                    * use by spec_write().
-                    */
-                       if (setsize)
+                       /*
+                        * Cache the size in bytes of the block device for later
+                        * use by spec_write().
+                        */
+                       if (setsize) {
                                vp->v_specdevsize = blkcnt * (u_int64_t)size512;
-                       else
-                       vp->v_specdevsize = (u_int64_t)0;       /* Default: Can't get */
-                       
+                       } else {
+                               vp->v_specdevsize = (u_int64_t)0; /* Default: Can't get */
+                       }
                        vnode_unlock(vp);
-
                }
-               return(error);
+               return error;
        default:
-               panic("spec_open type");
+               panic("spec_open type");
        }
-       return (0);
+       return 0;
 }
 
 /*
@@ -386,61 +465,106 @@ spec_read(struct vnop_read_args *ap)
        struct buf *bp;
        daddr64_t bn, nextbn;
        long bsize, bscale;
-       int devBlockSize=0;
+       int devBlockSize = 0;
        int n, on;
        int error = 0;
        dev_t dev;
 
 #if DIAGNOSTIC
-       if (uio->uio_rw != UIO_READ)
+       if (uio->uio_rw != UIO_READ) {
                panic("spec_read mode");
-       if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg))
+       }
+       if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg)) {
                panic("spec_read proc");
+       }
 #endif
-       if (uio_resid(uio) == 0)
-               return (0);
+       if (uio_resid(uio) == 0) {
+               return 0;
+       }
 
        switch (vp->v_type) {
-
        case VCHR:
-                if (cdevsw[major(vp->v_rdev)].d_type == D_DISK && vp->v_un.vu_specinfo->si_throttleable) {
-                       struct _throttle_io_info_t *throttle_info;
+       {
+               struct _throttle_io_info_t *throttle_info = NULL;
+               int thread_throttle_level;
+               uint64_t blkno = 0;
+               uint32_t iolen = 0;
+               int ddisk = 0;
+               int ktrace_code = DKIO_READ;
+               devBlockSize = vp->v_specsize;
+               uintptr_t our_id;
 
+               if (cdevsw[major(vp->v_rdev)].d_type == D_DISK) {
+                       ddisk = 1;
+               }
+
+               if (ddisk && vp->v_un.vu_specinfo->si_throttleable) {
                        throttle_info = &_throttle_io_info[vp->v_un.vu_specinfo->si_devbsdunit];
+                       thread_throttle_level = throttle_info_update_internal(throttle_info, NULL, 0, vp->v_un.vu_specinfo->si_isssd, TRUE, NULL);
+               }
+
+               if (kdebug_enable && ddisk) {
+                       if (devBlockSize == 0) {
+                               devBlockSize = 512;  // default sector size
+                       }
 
-                       throttle_info_update_internal(throttle_info, 0, vp->v_un.vu_specinfo->si_isssd);
-                }
+                       if (uio_offset(uio) && devBlockSize) {
+                               blkno = ((uint64_t) uio_offset(uio) / ((uint64_t)devBlockSize));
+                       }
+                       iolen = (int) uio_resid(uio);
+                       our_id = (uintptr_t)thread_tid(current_thread());
+                       KERNEL_DEBUG_CONSTANT_IST(KDEBUG_COMMON,
+                           (FSDBG_CODE(DBG_DKRW, ktrace_code)) | DBG_FUNC_NONE, our_id,
+                           vp->v_rdev, blkno, iolen, 0);
+               }
 
                error = (*cdevsw[major(vp->v_rdev)].d_read)
-                       (vp->v_rdev, uio, ap->a_ioflag);
+                   (vp->v_rdev, uio, ap->a_ioflag);
+
 
-               return (error);
+               if (kdebug_enable && ddisk) {
+                       uint32_t residual = (uint32_t)uio_resid(uio);
+                       ktrace_code |= DKIO_DONE;
+                       KERNEL_DEBUG_CONSTANT_IST(KDEBUG_COMMON,
+                           (FSDBG_CODE(DBG_DKRW, ktrace_code)) | DBG_FUNC_NONE, our_id,
+                           (uintptr_t)VM_KERNEL_ADDRPERM(vp), residual, error, 0);
+               }
+
+               if (throttle_info) {
+                       throttle_info_end_io_internal(throttle_info, thread_throttle_level);
+               }
+
+               return error;
+       }
 
        case VBLK:
-               if (uio->uio_offset < 0)
-                       return (EINVAL);
+               if (uio->uio_offset < 0) {
+                       return EINVAL;
+               }
 
                dev = vp->v_rdev;
 
                devBlockSize = vp->v_specsize;
 
-               if (devBlockSize > PAGE_SIZE) 
-                       return (EINVAL);
+               if (devBlockSize > PAGE_SIZE) {
+                       return EINVAL;
+               }
 
-               bscale = PAGE_SIZE / devBlockSize;
+               bscale = PAGE_SIZE / devBlockSize;
                bsize = bscale * devBlockSize;
 
                do {
                        on = uio->uio_offset % bsize;
 
-                       bn = (daddr64_t)((uio->uio_offset / devBlockSize) &(bscale - 1));
-                       
+                       bn = (daddr64_t)((uio->uio_offset / devBlockSize) & ~(bscale - 1));
+
                        if (vp->v_speclastr + bscale == bn) {
-                               nextbn = bn + bscale;
+                               nextbn = bn + bscale;
                                error = buf_breadn(vp, bn, (int)bsize, &nextbn,
-                                              (int *)&bsize, 1, NOCRED, &bp);
-                       } else
-                               error = buf_bread(vp, bn, (int)bsize, NOCRED, &bp);
+                                   (int *)&bsize, 1, NOCRED, &bp);
+                       } else {
+                               error = buf_bread(vp, bn, (int)bsize, NOCRED, &bp);
+                       }
 
                        vnode_lock(vp);
                        vp->v_speclastr = bn;
@@ -448,26 +572,28 @@ spec_read(struct vnop_read_args *ap)
 
                        n = bsize - buf_resid(bp);
                        if ((on > n) || error) {
-                               if (!error)
-                                       error = EINVAL;
+                               if (!error) {
+                                       error = EINVAL;
+                               }
                                buf_brelse(bp);
-                               return (error);
+                               return error;
                        }
                        n = min((unsigned)(n  - on), uio_resid(uio));
 
                        error = uiomove((char *)buf_dataptr(bp) + on, n, uio);
-                       if (n + on == bsize)
+                       if (n + on == bsize) {
                                buf_markaged(bp);
+                       }
                        buf_brelse(bp);
                } while (error == 0 && uio_resid(uio) > 0 && n != 0);
-               return (error);
+               return error;
 
        default:
                panic("spec_read type");
        }
        /* NOTREACHED */
 
-       return (0);
+       return 0;
 }
 
 /*
@@ -482,57 +608,101 @@ spec_write(struct vnop_write_args *ap)
        daddr64_t bn;
        int bsize, blkmask, bscale;
        int io_sync;
-       int devBlockSize=0;
+       int devBlockSize = 0;
        int n, on;
        int error = 0;
        dev_t dev;
 
 #if DIAGNOSTIC
-       if (uio->uio_rw != UIO_WRITE)
+       if (uio->uio_rw != UIO_WRITE) {
                panic("spec_write mode");
-       if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg))
+       }
+       if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg)) {
                panic("spec_write proc");
+       }
 #endif
 
        switch (vp->v_type) {
-
        case VCHR:
-                if (cdevsw[major(vp->v_rdev)].d_type == D_DISK && vp->v_un.vu_specinfo->si_throttleable) {
-                       struct _throttle_io_info_t *throttle_info;
+       {
+               struct _throttle_io_info_t *throttle_info = NULL;
+               int thread_throttle_level;
+               dev = vp->v_rdev;
+               devBlockSize = vp->v_specsize;
+               uint32_t iolen = 0;
+               uint64_t blkno = 0;
+               int ddisk = 0;
+               int ktrace_code = 0;  // write is implied; read must be OR'd in.
+               uintptr_t our_id;
+
+               if (cdevsw[major(dev)].d_type == D_DISK) {
+                       ddisk = 1;
+               }
 
+               if (ddisk && vp->v_un.vu_specinfo->si_throttleable) {
                        throttle_info = &_throttle_io_info[vp->v_un.vu_specinfo->si_devbsdunit];
 
-                       throttle_info_update_internal(throttle_info, 0, vp->v_un.vu_specinfo->si_isssd);
+                       thread_throttle_level = throttle_info_update_internal(throttle_info, NULL, 0, vp->v_un.vu_specinfo->si_isssd, TRUE, NULL);
 
-                       microuptime(&throttle_info->last_IO_timestamp);
-                }
+                       microuptime(&throttle_info->throttle_last_write_timestamp);
+               }
 
+               if (kdebug_enable && ddisk) {
+                       if (devBlockSize == 0) {
+                               devBlockSize = 512; // default sector size
+                       }
+                       if ((uio_offset(uio) != 0) && devBlockSize) {
+                               blkno = ((uint64_t)uio_offset(uio)) / ((uint64_t)devBlockSize);
+                       }
+                       iolen = (int)uio_resid(uio);
+                       our_id = (uintptr_t)thread_tid(current_thread());
+                       KERNEL_DEBUG_CONSTANT_IST(KDEBUG_COMMON,
+                           (FSDBG_CODE(DBG_DKRW, ktrace_code)) | DBG_FUNC_NONE, our_id,
+                           vp->v_rdev, blkno, iolen, 0);
+               }
                error = (*cdevsw[major(vp->v_rdev)].d_write)
-                       (vp->v_rdev, uio, ap->a_ioflag);
+                   (vp->v_rdev, uio, ap->a_ioflag);
+
+               if (kdebug_enable && ddisk) {
+                       //emit the I/O completion
+                       uint32_t residual = (uint32_t)uio_resid(uio);
+                       ktrace_code |= DKIO_DONE;
+                       KERNEL_DEBUG_CONSTANT_IST(KDEBUG_COMMON,
+                           (FSDBG_CODE(DBG_DKRW, ktrace_code)) | DBG_FUNC_NONE, our_id,
+                           (uintptr_t)VM_KERNEL_ADDRPERM(vp), residual, error, 0);
+               }
 
-               return (error);
+               if (throttle_info) {
+                       throttle_info_end_io_internal(throttle_info, thread_throttle_level);
+               }
+
+               return error;
+       }
 
        case VBLK:
-               if (uio_resid(uio) == 0)
-                       return (0);
-               if (uio->uio_offset < 0)
-                       return (EINVAL);
+               if (uio_resid(uio) == 0) {
+                       return 0;
+               }
+               if (uio->uio_offset < 0) {
+                       return EINVAL;
+               }
 
                io_sync = (ap->a_ioflag & IO_SYNC);
 
                dev = (vp->v_rdev);
 
                devBlockSize = vp->v_specsize;
-               if (devBlockSize > PAGE_SIZE)
-                       return(EINVAL);
+               if (devBlockSize > PAGE_SIZE) {
+                       return EINVAL;
+               }
 
-               bscale = PAGE_SIZE / devBlockSize;
+               bscale = PAGE_SIZE / devBlockSize;
                blkmask = bscale - 1;
                bsize = bscale * devBlockSize;
-               
+
 
                do {
-                       bn = (daddr64_t)((uio->uio_offset / devBlockSize) &blkmask);
+                       bn = (daddr64_t)((uio->uio_offset / devBlockSize) & ~blkmask);
                        on = uio->uio_offset % bsize;
 
                        n = min((unsigned)(bsize - on), uio_resid(uio));
@@ -550,48 +720,51 @@ spec_write(struct vnop_write_args *ap)
                        if (n == bsize &&
                            vp->v_specdevsize != (u_int64_t)0 &&
                            (uio->uio_offset + (u_int64_t)n) > vp->v_specdevsize) {
-                           /* reduce the size of the read to what is there */
-                           n = (uio->uio_offset + (u_int64_t)n) - vp->v_specdevsize;
+                               /* reduce the size of the read to what is there */
+                               n = (uio->uio_offset + (u_int64_t)n) - vp->v_specdevsize;
                        }
 
-                       if (n == bsize)
-                               bp = buf_getblk(vp, bn, bsize, 0, 0, BLK_WRITE);
-                       else
-                               error = (int)buf_bread(vp, bn, bsize, NOCRED, &bp);
+                       if (n == bsize) {
+                               bp = buf_getblk(vp, bn, bsize, 0, 0, BLK_WRITE);
+                       } else {
+                               error = (int)buf_bread(vp, bn, bsize, NOCRED, &bp);
+                       }
 
                        /* Translate downstream error for upstream, if needed */
-                       if (!error)
+                       if (!error) {
                                error = (int)buf_error(bp);
+                       }
                        if (error) {
                                buf_brelse(bp);
-                               return (error);
+                               return error;
                        }
                        n = min(n, bsize - buf_resid(bp));
 
                        error = uiomove((char *)buf_dataptr(bp) + on, n, uio);
                        if (error) {
                                buf_brelse(bp);
-                               return (error);
+                               return error;
                        }
                        buf_markaged(bp);
 
-                       if (io_sync) 
-                               error = buf_bwrite(bp);
-                       else {
-                               if ((n + on) == bsize)
-                                       error = buf_bawrite(bp);
-                               else
-                                       error = buf_bdwrite(bp);
+                       if (io_sync) {
+                               error = buf_bwrite(bp);
+                       } else {
+                               if ((n + on) == bsize) {
+                                       error = buf_bawrite(bp);
+                               } else {
+                                       error = buf_bdwrite(bp);
+                               }
                        }
                } while (error == 0 && uio_resid(uio) > 0 && n != 0);
-               return (error);
+               return error;
 
        default:
                panic("spec_write type");
        }
        /* NOTREACHED */
 
-       return (0);
+       return 0;
 }
 
 /*
@@ -602,21 +775,22 @@ spec_ioctl(struct vnop_ioctl_args *ap)
 {
        proc_t p = vfs_context_proc(ap->a_context);
        dev_t dev = ap->a_vp->v_rdev;
-       int     retval = 0;
+       int     retval = 0;
 
        KERNEL_DEBUG_CONSTANT(FSDBG_CODE(DBG_IOCTL, 0) | DBG_FUNC_START,
-                             (unsigned int)dev, (unsigned int)ap->a_command, (unsigned int)ap->a_fflag, (unsigned int)ap->a_vp->v_type, 0);
+           dev, ap->a_command, ap->a_fflag, ap->a_vp->v_type, 0);
 
        switch (ap->a_vp->v_type) {
-
        case VCHR:
                retval = (*cdevsw[major(dev)].d_ioctl)(dev, ap->a_command, ap->a_data,
-                                                      ap->a_fflag, p);
+                   ap->a_fflag, p);
                break;
 
        case VBLK:
-               retval = (*bdevsw[major(dev)].d_ioctl)(dev, ap->a_command, ap->a_data,
-                                                      ap->a_fflag, p);
+               retval = (*bdevsw[major(dev)].d_ioctl)(dev, ap->a_command, ap->a_data, ap->a_fflag, p);
+               if (!retval && ap->a_command == DKIOCSETBLOCKSIZE) {
+                       ap->a_vp->v_specsize = *(uint32_t *)ap->a_data;
+               }
                break;
 
        default:
@@ -624,9 +798,9 @@ spec_ioctl(struct vnop_ioctl_args *ap)
                /* NOTREACHED */
        }
        KERNEL_DEBUG_CONSTANT(FSDBG_CODE(DBG_IOCTL, 0) | DBG_FUNC_END,
-                             (unsigned int)dev, (unsigned int)ap->a_command, (unsigned int)ap->a_fflag, retval, 0);
+           dev, ap->a_command, ap->a_fflag, retval, 0);
 
-       return (retval);
+       return retval;
 }
 
 int
@@ -636,9 +810,8 @@ spec_select(struct vnop_select_args *ap)
        dev_t dev;
 
        switch (ap->a_vp->v_type) {
-
        default:
-               return (1);             /* XXX */
+               return 1;             /* XXX */
 
        case VCHR:
                dev = ap->a_vp->v_rdev;
@@ -646,29 +819,62 @@ spec_select(struct vnop_select_args *ap)
        }
 }
 
-static int filt_specattach(struct knote *kn);
+static int filt_specattach(struct knote *kn, struct kevent_qos_s *kev);
 
 int
-spec_kqfilter(vnode_t vp, struct knote *kn)
+spec_kqfilter(vnode_t vp, struct knote *kn, struct kevent_qos_s *kev)
 {
        dev_t dev;
-       int err = EINVAL;
 
+       assert(vnode_ischr(vp));
+
+       dev = vnode_specrdev(vp);
+
+#if NETWORKING
        /*
-        * For a few special kinds of devices, we can attach knotes.
-        * Each filter function must check whether the dev type matches it.
+        * Try a bpf device, as defined in bsd/net/bpf.c
+        * If it doesn't error out the attach, then it
+        * claimed it. Otherwise, fall through and try
+        * other attaches.
         */
-       dev = vnode_specrdev(vp);
+       int32_t tmp_flags = kn->kn_flags;
+       int64_t tmp_sdata = kn->kn_sdata;
+       int res;
 
-       if (vnode_istty(vp)) {
-               /* We can hook into TTYs... */
-               err = filt_specattach(kn);
-       } else {
-               /* Try a bpf device, as defined in bsd/net/bpf.c */
-               err = bpfkqfilter(dev, kn);
+       res = bpfkqfilter(dev, kn);
+       if ((kn->kn_flags & EV_ERROR) == 0) {
+               return res;
+       }
+       kn->kn_flags = tmp_flags;
+       kn->kn_sdata = tmp_sdata;
+#endif
+
+       if (major(dev) > nchrdev) {
+               knote_set_error(kn, ENXIO);
+               return 0;
+       }
+
+       kn->kn_vnode_kqok = !!(cdevsw_flags[major(dev)] & CDEVSW_SELECT_KQUEUE);
+       kn->kn_vnode_use_ofst = !!(cdevsw_flags[major(dev)] & CDEVSW_USE_OFFSET);
+
+       if (cdevsw_flags[major(dev)] & CDEVSW_IS_PTS) {
+               kn->kn_filtid = EVFILTID_PTSD;
+               return ptsd_kqfilter(dev, kn);
+       } else if (cdevsw_flags[major(dev)] & CDEVSW_IS_PTC) {
+               kn->kn_filtid = EVFILTID_PTMX;
+               return ptmx_kqfilter(dev, kn);
+       } else if (cdevsw[major(dev)].d_type == D_TTY && kn->kn_vnode_kqok) {
+               /*
+                * TTYs from drivers that use struct ttys use their own filter
+                * routines.  The PTC driver doesn't use the tty for character
+                * counts, so it must go through the select fallback.
+                */
+               kn->kn_filtid = EVFILTID_TTY;
+               return knote_fops(kn)->f_attach(kn, kev);
        }
 
-       return err;
+       /* Try to attach to other char special devices */
+       return filt_specattach(kn, kev);
 }
 
 /*
@@ -677,14 +883,15 @@ spec_kqfilter(vnode_t vp, struct knote *kn)
 int
 spec_fsync_internal(vnode_t vp, int waitfor, __unused vfs_context_t context)
 {
-       if (vp->v_type == VCHR)
-               return (0);
+       if (vp->v_type == VCHR) {
+               return 0;
+       }
        /*
         * Flush all dirty buffers associated with a block device.
         */
        buf_flushdirtyblks(vp, (waitfor == MNT_WAIT || waitfor == MNT_DWAIT), 0, "spec_fsync");
 
-       return (0);
+       return 0;
 }
 
 int
@@ -693,44 +900,44 @@ spec_fsync(struct vnop_fsync_args *ap)
        return spec_fsync_internal(ap->a_vp, ap->a_waitfor, ap->a_context);
 }
 
+
 /*
  * Just call the device strategy routine
  */
-extern int hard_throttle_on_root;
-void IOSleep(int);
+void throttle_init(void);
 
-// the low priority process may wait for at most LOWPRI_MAX_DELAY millisecond
-#define LOWPRI_INITIAL_WINDOW_MSECS 100
-#define LOWPRI_WINDOW_MSECS_INC        50
-#define LOWPRI_MAX_WINDOW_MSECS 200
-#define LOWPRI_MAX_WAITING_MSECS 200
 
-#if CONFIG_EMBEDDED
-#define LOWPRI_SLEEP_INTERVAL 5
+#if 0
+#define DEBUG_ALLOC_THROTTLE_INFO(format, debug_info, args...)  \
+       do {                                                    \
+              if ((debug_info)->alloc)                           \
+              printf("%s: "format, __FUNCTION__, ## args);     \
+       } while(0)
+
 #else
-#define LOWPRI_SLEEP_INTERVAL 2
+#define DEBUG_ALLOC_THROTTLE_INFO(format, debug_info, args...)
 #endif
 
-int    lowpri_IO_initial_window_msecs  = LOWPRI_INITIAL_WINDOW_MSECS;
-int    lowpri_IO_window_msecs_inc  = LOWPRI_WINDOW_MSECS_INC;
-int    lowpri_max_window_msecs  = LOWPRI_MAX_WINDOW_MSECS;
-int     lowpri_max_waiting_msecs = LOWPRI_MAX_WAITING_MSECS;
 
-#if 0 
-#define DEBUG_ALLOC_THROTTLE_INFO(format, debug_info, args...) \
-        do {                                                    \
-               if ((debug_info)->alloc)                           \
-               printf("%s: "format, __FUNCTION__, ## args);     \
-       } while(0)
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier1_window_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_windows_msecs[THROTTLE_LEVEL_TIER1], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier2_window_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_windows_msecs[THROTTLE_LEVEL_TIER2], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier3_window_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_windows_msecs[THROTTLE_LEVEL_TIER3], 0, "");
 
-#else 
-#define DEBUG_ALLOC_THROTTLE_INFO(format, debug_info, args...)
-#endif
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier1_io_period_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_msecs[THROTTLE_LEVEL_TIER1], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier2_io_period_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_msecs[THROTTLE_LEVEL_TIER2], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier3_io_period_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_msecs[THROTTLE_LEVEL_TIER3], 0, "");
+
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier1_io_period_ssd_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_ssd_msecs[THROTTLE_LEVEL_TIER1], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier2_io_period_ssd_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_ssd_msecs[THROTTLE_LEVEL_TIER2], 0, "");
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_tier3_io_period_ssd_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &throttle_io_period_ssd_msecs[THROTTLE_LEVEL_TIER3], 0, "");
+
+SYSCTL_INT(_debug, OID_AUTO, lowpri_throttle_enabled, CTLFLAG_RW | CTLFLAG_LOCKED, &lowpri_throttle_enabled, 0, "");
+
+
+static lck_grp_t        *throttle_lock_grp;
+static lck_attr_t       *throttle_lock_attr;
+static lck_grp_attr_t   *throttle_lock_grp_attr;
 
-SYSCTL_INT(_debug, OID_AUTO, lowpri_IO_initial_window_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &lowpri_IO_initial_window_msecs, LOWPRI_INITIAL_WINDOW_MSECS, "");
-SYSCTL_INT(_debug, OID_AUTO, lowpri_IO_window_inc, CTLFLAG_RW | CTLFLAG_LOCKED, &lowpri_IO_window_msecs_inc, LOWPRI_INITIAL_WINDOW_MSECS, "");
-SYSCTL_INT(_debug, OID_AUTO, lowpri_max_window_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &lowpri_max_window_msecs, LOWPRI_INITIAL_WINDOW_MSECS, "");
-SYSCTL_INT(_debug, OID_AUTO, lowpri_max_waiting_msecs, CTLFLAG_RW | CTLFLAG_LOCKED, &lowpri_max_waiting_msecs, LOWPRI_INITIAL_WINDOW_MSECS, "");
 
 /*
  * throttled I/O helper function
@@ -741,10 +948,11 @@ num_trailing_0(uint64_t n)
 {
        /*
         * since in most cases the number of trailing 0s is very small,
-     * we simply counting sequentially from the lowest bit
+        * we simply counting sequentially from the lowest bit
         */
-       if (n == 0)
+       if (n == 0) {
                return sizeof(n) * 8;
+       }
        int count = 0;
        while (!ISSET(n, 1)) {
                n >>= 1;
@@ -753,6 +961,7 @@ num_trailing_0(uint64_t n)
        return count;
 }
 
+
 /*
  * Release the reference and if the item was allocated and this is the last
  * reference then free it.
@@ -762,26 +971,30 @@ num_trailing_0(uint64_t n)
 static int
 throttle_info_rel(struct _throttle_io_info_t *info)
 {
-       SInt32 oldValue = OSDecrementAtomic(&info->refcnt);
+       SInt32 oldValue = OSDecrementAtomic(&info->throttle_refcnt);
 
-       DEBUG_ALLOC_THROTTLE_INFO("refcnt = %d info = %p\n", 
-               info, (int)(oldValue -1), info );
+       DEBUG_ALLOC_THROTTLE_INFO("refcnt = %d info = %p\n",
+           info, (int)(oldValue - 1), info );
 
        /* The reference count just went negative, very bad */
-       if (oldValue == 0)
+       if (oldValue == 0) {
                panic("throttle info ref cnt went negative!");
+       }
 
-       /* 
-        * Once reference count is zero, no one else should be able to take a 
-        * reference 
+       /*
+        * Once reference count is zero, no one else should be able to take a
+        * reference
         */
-       if ((info->refcnt == 0) && (info->alloc)) {
-               DEBUG_ALLOC_THROTTLE_INFO("Freeing info = %p\n", info, info );
-               FREE(info, M_TEMP); 
+       if ((info->throttle_refcnt == 0) && (info->throttle_alloc)) {
+               DEBUG_ALLOC_THROTTLE_INFO("Freeing info = %p\n", info);
+
+               lck_mtx_destroy(&info->throttle_lock, throttle_lock_grp);
+               FREE(info, M_TEMP);
        }
        return oldValue;
 }
 
+
 /*
  * Just take a reference on the throttle info structure.
  *
@@ -790,527 +1003,1595 @@ throttle_info_rel(struct _throttle_io_info_t *info)
 static SInt32
 throttle_info_ref(struct _throttle_io_info_t *info)
 {
-       SInt32 oldValue = OSIncrementAtomic(&info->refcnt);
+       SInt32 oldValue = OSIncrementAtomic(&info->throttle_refcnt);
 
-       DEBUG_ALLOC_THROTTLE_INFO("refcnt = %d info = %p\n", 
-               info, (int)(oldValue -1), info );
+       DEBUG_ALLOC_THROTTLE_INFO("refcnt = %d info = %p\n",
+           info, (int)(oldValue - 1), info );
        /* Allocated items should never have a reference of zero */
-       if (info->alloc && (oldValue == 0))
+       if (info->throttle_alloc && (oldValue == 0)) {
                panic("Taking a reference without calling create throttle info!\n");
+       }
 
        return oldValue;
 }
 
 /*
- * KPI routine
- *
- * Create and take a reference on a throttle info structure and return a
- * pointer for the file system to use when calling throttle_info_update.
- * Calling file system must have a matching release for every create.
+ * on entry the throttle_lock is held...
+ * this function is responsible for taking
+ * and dropping the reference on the info
+ * structure which will keep it from going
+ * away while the timer is running if it
+ * happens to have been dynamically allocated by
+ * a network fileystem kext which is now trying
+ * to free it
  */
-void *
-throttle_info_create(void)
+static uint32_t
+throttle_timer_start(struct _throttle_io_info_t *info, boolean_t update_io_count, int wakelevel)
 {
-       struct _throttle_io_info_t *info; 
+       struct timeval  elapsed;
+       struct timeval  now;
+       struct timeval  period;
+       uint64_t        elapsed_msecs;
+       int             throttle_level;
+       int             level;
+       int             msecs;
+       boolean_t       throttled = FALSE;
+       boolean_t       need_timer = FALSE;
+
+       microuptime(&now);
+
+       if (update_io_count == TRUE) {
+               info->throttle_io_count_begin = info->throttle_io_count;
+               info->throttle_io_period_num++;
+
+               while (wakelevel >= THROTTLE_LEVEL_THROTTLED) {
+                       info->throttle_start_IO_period_timestamp[wakelevel--] = now;
+               }
 
-       MALLOC(info, struct _throttle_io_info_t *, sizeof(*info), M_TEMP, M_ZERO | M_WAITOK);
-       /* Should never happen but just in case */
-       if (info == NULL)
-               return NULL;
-       /* Mark that this one was allocated and needs to be freed */
-       DEBUG_ALLOC_THROTTLE_INFO("Creating info = %p\n", info, info );
-       info->alloc = TRUE;
-       /* Take a reference */
-       OSIncrementAtomic(&info->refcnt);
-       return info;
-}
+               info->throttle_min_timer_deadline = now;
 
-/*
- * KPI routine
- *
- * Release the throttle info pointer if all the reference are gone. Should be 
- * called to release reference taken by throttle_info_create 
- */ 
-void
-throttle_info_release(void *throttle_info)
-{
-       DEBUG_ALLOC_THROTTLE_INFO("Releaseing info = %p\n",
-               (struct _throttle_io_info_t *)throttle_info,
-               (struct _throttle_io_info_t *)throttle_info);
-       if (throttle_info) /* Just to be careful */
-               throttle_info_rel(throttle_info);
-}
+               msecs = info->throttle_io_periods[THROTTLE_LEVEL_THROTTLED];
+               period.tv_sec = msecs / 1000;
+               period.tv_usec = (msecs % 1000) * 1000;
 
-/*
- * KPI routine
- *
- * File Systems that create an info structure, need to call this routine in
- * their mount routine (used by cluster code). File Systems that call this in
- * their mount routines must call throttle_info_mount_rel in their unmount
- * routines. 
- */
-void 
-throttle_info_mount_ref(mount_t mp, void *throttle_info)
-{
-       if ((throttle_info == NULL) || (mp == NULL))
-               return;
-       throttle_info_ref(throttle_info);
-       /* We already have a reference release it before adding the new one */
-       if (mp->mnt_throttle_info)
-               throttle_info_rel(mp->mnt_throttle_info);
-       mp->mnt_throttle_info = throttle_info;
-}
+               timevaladd(&info->throttle_min_timer_deadline, &period);
+       }
+       for (throttle_level = THROTTLE_LEVEL_START; throttle_level < THROTTLE_LEVEL_END; throttle_level++) {
+               elapsed = now;
+               timevalsub(&elapsed, &info->throttle_window_start_timestamp[throttle_level]);
+               elapsed_msecs = (uint64_t)elapsed.tv_sec * (uint64_t)1000 + (elapsed.tv_usec / 1000);
+
+               for (level = throttle_level + 1; level <= THROTTLE_LEVEL_END; level++) {
+                       if (!TAILQ_EMPTY(&info->throttle_uthlist[level])) {
+                               if (elapsed_msecs < (uint64_t)throttle_windows_msecs[level] || info->throttle_inflight_count[throttle_level]) {
+                                       /*
+                                        * we had an I/O occur at a higher priority tier within
+                                        * this tier's throttle window
+                                        */
+                                       throttled = TRUE;
+                               }
+                               /*
+                                * we assume that the windows are the same or longer
+                                * as we drop through the throttling tiers...  thus
+                                * we can stop looking once we run into a tier with
+                                * threads to schedule regardless of whether it's
+                                * still in its throttling window or not
+                                */
+                               break;
+                       }
+               }
+               if (throttled == TRUE) {
+                       break;
+               }
+       }
+       if (throttled == TRUE) {
+               uint64_t        deadline = 0;
+               struct timeval  target;
+               struct timeval  min_target;
 
-/*
- * Private KPI routine
- *
- * return a handle for accessing throttle_info given a throttle_mask.  The
- * handle must be released by throttle_info_rel_by_mask
- */
-int
-throttle_info_ref_by_mask(uint64_t throttle_mask,
-                                                 throttle_info_handle_t *throttle_info_handle)
-{
-       int dev_index;
-       struct _throttle_io_info_t *info;
+               /*
+                * we've got at least one tier still in a throttled window
+                * so we need a timer running... compute the next deadline
+                * and schedule it
+                */
+               for (level = throttle_level + 1; level <= THROTTLE_LEVEL_END; level++) {
+                       if (TAILQ_EMPTY(&info->throttle_uthlist[level])) {
+                               continue;
+                       }
 
-       if (throttle_info_handle == NULL)
-               return EINVAL;
-       
-       dev_index = num_trailing_0(throttle_mask);
-       info = &_throttle_io_info[dev_index];
-       throttle_info_ref(info);
-       *(struct _throttle_io_info_t**)throttle_info_handle = info;
-       return 0;
-}
+                       target = info->throttle_start_IO_period_timestamp[level];
 
-/*
- * Private KPI routine
- *
- * release the handle obtained by throttle_info_ref_by_mask
- */
-void
-throttle_info_rel_by_mask(throttle_info_handle_t throttle_info_handle)
-{
-       /* for now the handle is just a pointer to _throttle_io_info_t */
-       throttle_info_rel((struct _throttle_io_info_t*)throttle_info_handle);
-}
+                       msecs = info->throttle_io_periods[level];
+                       period.tv_sec = msecs / 1000;
+                       period.tv_usec = (msecs % 1000) * 1000;
 
-/*
- * KPI routine
- *
- * File Systems that throttle_info_mount_ref, must call this routine in their
- * umount routine.
- */ 
-void
-throttle_info_mount_rel(mount_t mp)
-{
-       if (mp->mnt_throttle_info)
-               throttle_info_rel(mp->mnt_throttle_info);
-       mp->mnt_throttle_info = NULL;
-}
+                       timevaladd(&target, &period);
 
-void
-throttle_info_get_last_io_time(mount_t mp, struct timeval *tv)
-{
-       struct _throttle_io_info_t *info;
+                       if (need_timer == FALSE || timevalcmp(&target, &min_target, <)) {
+                               min_target = target;
+                               need_timer = TRUE;
+                       }
+               }
+               if (timevalcmp(&info->throttle_min_timer_deadline, &now, >)) {
+                       if (timevalcmp(&info->throttle_min_timer_deadline, &min_target, >)) {
+                               min_target = info->throttle_min_timer_deadline;
+                       }
+               }
 
-       if (mp == NULL)
-           info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
-       else if (mp->mnt_throttle_info == NULL)
-           info = &_throttle_io_info[mp->mnt_devbsdunit];
-       else
-           info = mp->mnt_throttle_info;
+               if (info->throttle_timer_active) {
+                       if (thread_call_cancel(info->throttle_timer_call) == FALSE) {
+                               /*
+                                * couldn't kill the timer because it's already
+                                * been dispatched, so don't try to start a new
+                                * one... once we drop the lock, the timer will
+                                * proceed and eventually re-run this function
+                                */
+                               need_timer = FALSE;
+                       } else {
+                               info->throttle_timer_active = 0;
+                       }
+               }
+               if (need_timer == TRUE) {
+                       /*
+                        * This is defined as an int (32-bit) rather than a 64-bit
+                        * value because it would need a really big period in the
+                        * order of ~500 days to overflow this. So, we let this be
+                        * 32-bit which allows us to use the clock_interval_to_deadline()
+                        * routine.
+                        */
+                       int     target_msecs;
 
-       *tv = info->last_IO_timestamp;
-}
+                       if (info->throttle_timer_ref == 0) {
+                               /*
+                                * take a reference for the timer
+                                */
+                               throttle_info_ref(info);
 
-void
-update_last_io_time(mount_t mp)
-{
-       struct _throttle_io_info_t *info;
-               
-       if (mp == NULL)
-           info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
-       else if (mp->mnt_throttle_info == NULL)
-           info = &_throttle_io_info[mp->mnt_devbsdunit];
-       else
-           info = mp->mnt_throttle_info;
+                               info->throttle_timer_ref = 1;
+                       }
+                       elapsed = min_target;
+                       timevalsub(&elapsed, &now);
+                       target_msecs = elapsed.tv_sec * 1000 + elapsed.tv_usec / 1000;
 
-       microuptime(&info->last_IO_timestamp);
-}
+                       if (target_msecs <= 0) {
+                               /*
+                                * we may have computed a deadline slightly in the past
+                                * due to various factors... if so, just set the timer
+                                * to go off in the near future (we don't need to be precise)
+                                */
+                               target_msecs = 1;
+                       }
+                       clock_interval_to_deadline(target_msecs, 1000000, &deadline);
 
+                       thread_call_enter_delayed(info->throttle_timer_call, deadline);
+                       info->throttle_timer_active = 1;
+               }
+       }
+       return throttle_level;
+}
+
+
+static void
+throttle_timer(struct _throttle_io_info_t *info)
+{
+       uthread_t       ut, utlist;
+       struct timeval  elapsed;
+       struct timeval  now;
+       uint64_t        elapsed_msecs;
+       int             throttle_level;
+       int             level;
+       int             wake_level;
+       caddr_t         wake_address = NULL;
+       boolean_t       update_io_count = FALSE;
+       boolean_t       need_wakeup = FALSE;
+       boolean_t       need_release = FALSE;
+
+       ut = NULL;
+       lck_mtx_lock(&info->throttle_lock);
+
+       info->throttle_timer_active = 0;
+       microuptime(&now);
+
+       elapsed = now;
+       timevalsub(&elapsed, &info->throttle_start_IO_period_timestamp[THROTTLE_LEVEL_THROTTLED]);
+       elapsed_msecs = (uint64_t)elapsed.tv_sec * (uint64_t)1000 + (elapsed.tv_usec / 1000);
+
+       if (elapsed_msecs >= (uint64_t)info->throttle_io_periods[THROTTLE_LEVEL_THROTTLED]) {
+               wake_level = info->throttle_next_wake_level;
+
+               for (level = THROTTLE_LEVEL_START; level < THROTTLE_LEVEL_END; level++) {
+                       elapsed = now;
+                       timevalsub(&elapsed, &info->throttle_start_IO_period_timestamp[wake_level]);
+                       elapsed_msecs = (uint64_t)elapsed.tv_sec * (uint64_t)1000 + (elapsed.tv_usec / 1000);
+
+                       if (elapsed_msecs >= (uint64_t)info->throttle_io_periods[wake_level] && !TAILQ_EMPTY(&info->throttle_uthlist[wake_level])) {
+                               /*
+                                * we're closing out the current IO period...
+                                * if we have a waiting thread, wake it up
+                                * after we have reset the I/O window info
+                                */
+                               need_wakeup = TRUE;
+                               update_io_count = TRUE;
+
+                               info->throttle_next_wake_level = wake_level - 1;
+
+                               if (info->throttle_next_wake_level == THROTTLE_LEVEL_START) {
+                                       info->throttle_next_wake_level = THROTTLE_LEVEL_END;
+                               }
+
+                               break;
+                       }
+                       wake_level--;
+
+                       if (wake_level == THROTTLE_LEVEL_START) {
+                               wake_level = THROTTLE_LEVEL_END;
+                       }
+               }
+       }
+       if (need_wakeup == TRUE) {
+               if (!TAILQ_EMPTY(&info->throttle_uthlist[wake_level])) {
+                       ut = (uthread_t)TAILQ_FIRST(&info->throttle_uthlist[wake_level]);
+                       TAILQ_REMOVE(&info->throttle_uthlist[wake_level], ut, uu_throttlelist);
+                       ut->uu_on_throttlelist = THROTTLE_LEVEL_NONE;
+                       ut->uu_is_throttled = false;
+
+                       wake_address = (caddr_t)&ut->uu_on_throttlelist;
+               }
+       } else {
+               wake_level = THROTTLE_LEVEL_START;
+       }
+
+       throttle_level = throttle_timer_start(info, update_io_count, wake_level);
+
+       if (wake_address != NULL) {
+               wakeup(wake_address);
+       }
+
+       for (level = THROTTLE_LEVEL_THROTTLED; level <= throttle_level; level++) {
+               TAILQ_FOREACH_SAFE(ut, &info->throttle_uthlist[level], uu_throttlelist, utlist) {
+                       TAILQ_REMOVE(&info->throttle_uthlist[level], ut, uu_throttlelist);
+                       ut->uu_on_throttlelist = THROTTLE_LEVEL_NONE;
+                       ut->uu_is_throttled = false;
+
+                       wakeup(&ut->uu_on_throttlelist);
+               }
+       }
+       if (info->throttle_timer_active == 0 && info->throttle_timer_ref) {
+               info->throttle_timer_ref = 0;
+               need_release = TRUE;
+       }
+       lck_mtx_unlock(&info->throttle_lock);
+
+       if (need_release == TRUE) {
+               throttle_info_rel(info);
+       }
+}
+
+
+static int
+throttle_add_to_list(struct _throttle_io_info_t *info, uthread_t ut, int mylevel, boolean_t insert_tail)
+{
+       boolean_t start_timer = FALSE;
+       int level = THROTTLE_LEVEL_START;
+
+       if (TAILQ_EMPTY(&info->throttle_uthlist[mylevel])) {
+               info->throttle_start_IO_period_timestamp[mylevel] = info->throttle_last_IO_timestamp[mylevel];
+               start_timer = TRUE;
+       }
+
+       if (insert_tail == TRUE) {
+               TAILQ_INSERT_TAIL(&info->throttle_uthlist[mylevel], ut, uu_throttlelist);
+       } else {
+               TAILQ_INSERT_HEAD(&info->throttle_uthlist[mylevel], ut, uu_throttlelist);
+       }
+
+       ut->uu_on_throttlelist = mylevel;
+
+       if (start_timer == TRUE) {
+               /* we may need to start or rearm the timer */
+               level = throttle_timer_start(info, FALSE, THROTTLE_LEVEL_START);
+
+               if (level == THROTTLE_LEVEL_END) {
+                       if (ut->uu_on_throttlelist >= THROTTLE_LEVEL_THROTTLED) {
+                               TAILQ_REMOVE(&info->throttle_uthlist[ut->uu_on_throttlelist], ut, uu_throttlelist);
+
+                               ut->uu_on_throttlelist = THROTTLE_LEVEL_NONE;
+                       }
+               }
+       }
+       return level;
+}
+
+static void
+throttle_init_throttle_window(void)
+{
+       int throttle_window_size;
+
+       /*
+        * The hierarchy of throttle window values is as follows:
+        * - Global defaults
+        * - Device tree properties
+        * - Boot-args
+        * All values are specified in msecs.
+        */
+
+       /* Override global values with device-tree properties */
+       if (PE_get_default("kern.io_throttle_window_tier1", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER1] = throttle_window_size;
+       }
+
+       if (PE_get_default("kern.io_throttle_window_tier2", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER2] = throttle_window_size;
+       }
+
+       if (PE_get_default("kern.io_throttle_window_tier3", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER3] = throttle_window_size;
+       }
+
+       /* Override with boot-args */
+       if (PE_parse_boot_argn("io_throttle_window_tier1", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER1] = throttle_window_size;
+       }
+
+       if (PE_parse_boot_argn("io_throttle_window_tier2", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER2] = throttle_window_size;
+       }
+
+       if (PE_parse_boot_argn("io_throttle_window_tier3", &throttle_window_size, sizeof(throttle_window_size))) {
+               throttle_windows_msecs[THROTTLE_LEVEL_TIER3] = throttle_window_size;
+       }
+}
+
+static void
+throttle_init_throttle_period(struct _throttle_io_info_t *info, boolean_t isssd)
+{
+       int throttle_period_size;
+
+       /*
+        * The hierarchy of throttle period values is as follows:
+        * - Global defaults
+        * - Device tree properties
+        * - Boot-args
+        * All values are specified in msecs.
+        */
+
+       /* Assign global defaults */
+       if ((isssd == TRUE) && (info->throttle_is_fusion_with_priority == 0)) {
+               info->throttle_io_periods = &throttle_io_period_ssd_msecs[0];
+       } else {
+               info->throttle_io_periods = &throttle_io_period_msecs[0];
+       }
+
+       /* Override global values with device-tree properties */
+       if (PE_get_default("kern.io_throttle_period_tier1", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER1] = throttle_period_size;
+       }
+
+       if (PE_get_default("kern.io_throttle_period_tier2", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER2] = throttle_period_size;
+       }
+
+       if (PE_get_default("kern.io_throttle_period_tier3", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER3] = throttle_period_size;
+       }
+
+       /* Override with boot-args */
+       if (PE_parse_boot_argn("io_throttle_period_tier1", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER1] = throttle_period_size;
+       }
+
+       if (PE_parse_boot_argn("io_throttle_period_tier2", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER2] = throttle_period_size;
+       }
 
-#if CONFIG_EMBEDDED
+       if (PE_parse_boot_argn("io_throttle_period_tier3", &throttle_period_size, sizeof(throttle_period_size))) {
+               info->throttle_io_periods[THROTTLE_LEVEL_TIER3] = throttle_period_size;
+       }
+}
+
+#if CONFIG_IOSCHED
+extern  void vm_io_reprioritize_init(void);
+int     iosched_enabled = 1;
+#endif
+
+void
+throttle_init(void)
+{
+       struct _throttle_io_info_t *info;
+       int     i;
+       int     level;
+#if CONFIG_IOSCHED
+       int     iosched;
+#endif
+       /*
+        * allocate lock group attribute and group
+        */
+       throttle_lock_grp_attr = lck_grp_attr_alloc_init();
+       throttle_lock_grp = lck_grp_alloc_init("throttle I/O", throttle_lock_grp_attr);
+
+       /* Update throttle parameters based on device tree configuration */
+       throttle_init_throttle_window();
+
+       /*
+        * allocate the lock attribute
+        */
+       throttle_lock_attr = lck_attr_alloc_init();
+
+       for (i = 0; i < LOWPRI_MAX_NUM_DEV; i++) {
+               info = &_throttle_io_info[i];
+
+               lck_mtx_init(&info->throttle_lock, throttle_lock_grp, throttle_lock_attr);
+               info->throttle_timer_call = thread_call_allocate((thread_call_func_t)throttle_timer, (thread_call_param_t)info);
+
+               for (level = 0; level <= THROTTLE_LEVEL_END; level++) {
+                       TAILQ_INIT(&info->throttle_uthlist[level]);
+                       info->throttle_last_IO_pid[level] = 0;
+                       info->throttle_inflight_count[level] = 0;
+               }
+               info->throttle_next_wake_level = THROTTLE_LEVEL_END;
+               info->throttle_disabled = 0;
+               info->throttle_is_fusion_with_priority = 0;
+       }
+#if CONFIG_IOSCHED
+       if (PE_parse_boot_argn("iosched", &iosched, sizeof(iosched))) {
+               iosched_enabled = iosched;
+       }
+       if (iosched_enabled) {
+               /* Initialize I/O Reprioritization mechanism */
+               vm_io_reprioritize_init();
+       }
+#endif
+}
+
+void
+sys_override_io_throttle(boolean_t enable_override)
+{
+       if (enable_override) {
+               lowpri_throttle_enabled = 0;
+       } else {
+               lowpri_throttle_enabled = 1;
+       }
+}
+
+int rethrottle_wakeups = 0;
+
+/*
+ * the uu_rethrottle_lock is used to synchronize this function
+ * with "throttle_lowpri_io" which is where a throttled thread
+ * will block... that function will grab this lock before beginning
+ * it's decision making process concerning the need to block, and
+ * hold it through the assert_wait.  When that thread is awakened
+ * for any reason (timer or rethrottle), it will reacquire the
+ * uu_rethrottle_lock before determining if it really is ok for
+ * it to now run.  This is the point at which the thread could
+ * enter a different throttling queue and reblock or return from
+ * the throttle w/o having waited out it's entire throttle if
+ * the rethrottle has now moved it out of any currently
+ * active throttle window.
+ *
+ *
+ * NOTES:
+ * 1 - This may be called with the task lock held.
+ * 2 - This may be called with preemption and interrupts disabled
+ *     in the kqueue wakeup path so we can't take the throttle_lock which is a mutex
+ * 3 - This cannot safely dereference uu_throttle_info, as it may
+ *     get deallocated out from under us
+ */
+
+void
+rethrottle_thread(uthread_t ut)
+{
+       /*
+        * If uthread doesn't have throttle state, then there's no chance
+        * of it needing a rethrottle.
+        */
+       if (ut->uu_throttle_info == NULL) {
+               return;
+       }
+
+       boolean_t s = ml_set_interrupts_enabled(FALSE);
+       lck_spin_lock(&ut->uu_rethrottle_lock);
 
-int throttle_get_io_policy(struct uthread **ut)
+       if (!ut->uu_is_throttled) {
+               ut->uu_was_rethrottled = true;
+       } else {
+               int my_new_level = throttle_get_thread_throttle_level(ut);
+
+               if (my_new_level != ut->uu_on_throttlelist) {
+                       /*
+                        * ut is currently blocked (as indicated by
+                        * ut->uu_is_throttled == true)
+                        * and we're changing it's throttle level, so
+                        * we need to wake it up.
+                        */
+                       ut->uu_is_throttled = false;
+                       wakeup(&ut->uu_on_throttlelist);
+
+                       rethrottle_wakeups++;
+                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 102)), thread_tid(ut->uu_thread), ut->uu_on_throttlelist, my_new_level, 0, 0);
+               }
+       }
+       lck_spin_unlock(&ut->uu_rethrottle_lock);
+       ml_set_interrupts_enabled(s);
+}
+
+
+/*
+ * KPI routine
+ *
+ * Create and take a reference on a throttle info structure and return a
+ * pointer for the file system to use when calling throttle_info_update.
+ * Calling file system must have a matching release for every create.
+ */
+void *
+throttle_info_create(void)
+{
+       struct _throttle_io_info_t *info;
+       int     level;
+
+       MALLOC(info, struct _throttle_io_info_t *, sizeof(*info), M_TEMP, M_ZERO | M_WAITOK);
+       /* Should never happen but just in case */
+       if (info == NULL) {
+               return NULL;
+       }
+       /* Mark that this one was allocated and needs to be freed */
+       DEBUG_ALLOC_THROTTLE_INFO("Creating info = %p\n", info, info );
+       info->throttle_alloc = TRUE;
+
+       lck_mtx_init(&info->throttle_lock, throttle_lock_grp, throttle_lock_attr);
+       info->throttle_timer_call = thread_call_allocate((thread_call_func_t)throttle_timer, (thread_call_param_t)info);
+
+       for (level = 0; level <= THROTTLE_LEVEL_END; level++) {
+               TAILQ_INIT(&info->throttle_uthlist[level]);
+       }
+       info->throttle_next_wake_level = THROTTLE_LEVEL_END;
+
+       /* Take a reference */
+       OSIncrementAtomic(&info->throttle_refcnt);
+       return info;
+}
+
+/*
+ * KPI routine
+ *
+ * Release the throttle info pointer if all the reference are gone. Should be
+ * called to release reference taken by throttle_info_create
+ */
+void
+throttle_info_release(void *throttle_info)
+{
+       DEBUG_ALLOC_THROTTLE_INFO("Releaseing info = %p\n",
+           (struct _throttle_io_info_t *)throttle_info,
+           (struct _throttle_io_info_t *)throttle_info);
+       if (throttle_info) { /* Just to be careful */
+               throttle_info_rel(throttle_info);
+       }
+}
+
+/*
+ * KPI routine
+ *
+ * File Systems that create an info structure, need to call this routine in
+ * their mount routine (used by cluster code). File Systems that call this in
+ * their mount routines must call throttle_info_mount_rel in their unmount
+ * routines.
+ */
+void
+throttle_info_mount_ref(mount_t mp, void *throttle_info)
+{
+       if ((throttle_info == NULL) || (mp == NULL)) {
+               return;
+       }
+       throttle_info_ref(throttle_info);
+
+       /*
+        * We already have a reference release it before adding the new one
+        */
+       if (mp->mnt_throttle_info) {
+               throttle_info_rel(mp->mnt_throttle_info);
+       }
+       mp->mnt_throttle_info = throttle_info;
+}
+
+/*
+ * Private KPI routine
+ *
+ * return a handle for accessing throttle_info given a throttle_mask.  The
+ * handle must be released by throttle_info_rel_by_mask
+ */
+int
+throttle_info_ref_by_mask(uint64_t throttle_mask, throttle_info_handle_t *throttle_info_handle)
+{
+       int     dev_index;
+       struct _throttle_io_info_t *info;
+
+       if (throttle_info_handle == NULL) {
+               return EINVAL;
+       }
+
+       dev_index = num_trailing_0(throttle_mask);
+       info = &_throttle_io_info[dev_index];
+       throttle_info_ref(info);
+       *(struct _throttle_io_info_t**)throttle_info_handle = info;
+
+       return 0;
+}
+
+/*
+ * Private KPI routine
+ *
+ * release the handle obtained by throttle_info_ref_by_mask
+ */
+void
+throttle_info_rel_by_mask(throttle_info_handle_t throttle_info_handle)
+{
+       /*
+        * for now the handle is just a pointer to _throttle_io_info_t
+        */
+       throttle_info_rel((struct _throttle_io_info_t*)throttle_info_handle);
+}
+
+/*
+ * KPI routine
+ *
+ * File Systems that throttle_info_mount_ref, must call this routine in their
+ * umount routine.
+ */
+void
+throttle_info_mount_rel(mount_t mp)
+{
+       if (mp->mnt_throttle_info) {
+               throttle_info_rel(mp->mnt_throttle_info);
+       }
+       mp->mnt_throttle_info = NULL;
+}
+
+/*
+ * Reset throttling periods for the given mount point
+ *
+ * private interface used by disk conditioner to reset
+ * throttling periods when 'is_ssd' status changes
+ */
+void
+throttle_info_mount_reset_period(mount_t mp, int isssd)
+{
+       struct _throttle_io_info_t *info;
+
+       if (mp == NULL) {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       } else if (mp->mnt_throttle_info == NULL) {
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = mp->mnt_throttle_info;
+       }
+
+       throttle_init_throttle_period(info, isssd);
+}
+
+void
+throttle_info_get_last_io_time(mount_t mp, struct timeval *tv)
+{
+       struct _throttle_io_info_t *info;
+
+       if (mp == NULL) {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       } else if (mp->mnt_throttle_info == NULL) {
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = mp->mnt_throttle_info;
+       }
+
+       *tv = info->throttle_last_write_timestamp;
+}
+
+void
+update_last_io_time(mount_t mp)
+{
+       struct _throttle_io_info_t *info;
+
+       if (mp == NULL) {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       } else if (mp->mnt_throttle_info == NULL) {
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = mp->mnt_throttle_info;
+       }
+
+       microuptime(&info->throttle_last_write_timestamp);
+       if (mp != NULL) {
+               mp->mnt_last_write_completed_timestamp = info->throttle_last_write_timestamp;
+       }
+}
+
+int
+throttle_get_io_policy(uthread_t *ut)
+{
+       if (ut != NULL) {
+               *ut = get_bsdthread_info(current_thread());
+       }
+
+       return proc_get_effective_thread_policy(current_thread(), TASK_POLICY_IO);
+}
+
+int
+throttle_get_passive_io_policy(uthread_t *ut)
+{
+       if (ut != NULL) {
+               *ut = get_bsdthread_info(current_thread());
+       }
+
+       return proc_get_effective_thread_policy(current_thread(), TASK_POLICY_PASSIVE_IO);
+}
+
+
+static int
+throttle_get_thread_throttle_level(uthread_t ut)
+{
+       uthread_t *ut_p = (ut == NULL) ? &ut : NULL;
+       int io_tier = throttle_get_io_policy(ut_p);
+
+       return throttle_get_thread_throttle_level_internal(ut, io_tier);
+}
+
+/*
+ * Return a throttle level given an existing I/O tier (such as returned by throttle_get_io_policy)
+ */
+static int
+throttle_get_thread_throttle_level_internal(uthread_t ut, int io_tier)
+{
+       int thread_throttle_level = io_tier;
+       int user_idle_level;
+
+       assert(ut != NULL);
+
+       /* Bootcache misses should always be throttled */
+       if (ut->uu_throttle_bc) {
+               thread_throttle_level = THROTTLE_LEVEL_TIER3;
+       }
+
+       /*
+        * Issue tier3 I/O as tier2 when the user is idle
+        * to allow maintenance tasks to make more progress.
+        *
+        * Assume any positive idle level is enough... for now it's
+        * only ever 0 or 128 but this is not defined anywhere.
+        */
+       if (thread_throttle_level >= THROTTLE_LEVEL_TIER3) {
+               user_idle_level = timer_get_user_idle_level();
+               if (user_idle_level > 0) {
+                       thread_throttle_level--;
+               }
+       }
+
+       return thread_throttle_level;
+}
+
+/*
+ * I/O will be throttled if either of the following are true:
+ *   - Higher tiers have in-flight I/O
+ *   - The time delta since the last start/completion of a higher tier is within the throttle window interval
+ *
+ * In-flight I/O is bookended by throttle_info_update_internal/throttle_info_end_io_internal
+ */
+static int
+throttle_io_will_be_throttled_internal(void * throttle_info, int * mylevel, int * throttling_level)
+{
+       struct _throttle_io_info_t *info = throttle_info;
+       struct timeval elapsed;
+       struct timeval now;
+       uint64_t elapsed_msecs;
+       int     thread_throttle_level;
+       int     throttle_level;
+
+       if ((thread_throttle_level = throttle_get_thread_throttle_level(NULL)) < THROTTLE_LEVEL_THROTTLED) {
+               return THROTTLE_DISENGAGED;
+       }
+
+       microuptime(&now);
+
+       for (throttle_level = THROTTLE_LEVEL_START; throttle_level < thread_throttle_level; throttle_level++) {
+               if (info->throttle_inflight_count[throttle_level]) {
+                       break;
+               }
+               elapsed = now;
+               timevalsub(&elapsed, &info->throttle_window_start_timestamp[throttle_level]);
+               elapsed_msecs = (uint64_t)elapsed.tv_sec * (uint64_t)1000 + (elapsed.tv_usec / 1000);
+
+               if (elapsed_msecs < (uint64_t)throttle_windows_msecs[thread_throttle_level]) {
+                       break;
+               }
+       }
+       if (throttle_level >= thread_throttle_level) {
+               /*
+                * we're beyond all of the throttle windows
+                * that affect the throttle level of this thread,
+                * so go ahead and treat as normal I/O
+                */
+               return THROTTLE_DISENGAGED;
+       }
+       if (mylevel) {
+               *mylevel = thread_throttle_level;
+       }
+       if (throttling_level) {
+               *throttling_level = throttle_level;
+       }
+
+       if (info->throttle_io_count != info->throttle_io_count_begin) {
+               /*
+                * we've already issued at least one throttleable I/O
+                * in the current I/O window, so avoid issuing another one
+                */
+               return THROTTLE_NOW;
+       }
+       /*
+        * we're in the throttle window, so
+        * cut the I/O size back
+        */
+       return THROTTLE_ENGAGED;
+}
+
+/*
+ * If we have a mount point and it has a throttle info pointer then
+ * use it to do the check, otherwise use the device unit number to find
+ * the correct throttle info array element.
+ */
+int
+throttle_io_will_be_throttled(__unused int lowpri_window_msecs, mount_t mp)
 {
-       int policy = IOPOL_DEFAULT;
-       proc_t p = current_proc();
+       struct _throttle_io_info_t      *info;
 
-       *ut = get_bsdthread_info(current_thread());
-               
-       if (p != NULL)
-               policy = p->p_iopol_disk;
-
-       if (*ut != NULL) {
-               // the I/O policy of the thread overrides that of the process
-               // unless the I/O policy of the thread is default
-               if ((*ut)->uu_iopol_disk != IOPOL_DEFAULT)
-                       policy = (*ut)->uu_iopol_disk;
+       /*
+        * Should we just return zero if no mount point
+        */
+       if (mp == NULL) {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       } else if (mp->mnt_throttle_info == NULL) {
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = mp->mnt_throttle_info;
        }
-       return policy;
-}
-#else
 
-int throttle_get_io_policy(__unused struct uthread **ut)
-{
-       *ut = get_bsdthread_info(current_thread());
+       if (info->throttle_is_fusion_with_priority) {
+               uthread_t ut = get_bsdthread_info(current_thread());
+               if (ut->uu_lowpri_window == 0) {
+                       return THROTTLE_DISENGAGED;
+               }
+       }
 
-       return (proc_get_task_selfdiskacc());
+       if (info->throttle_disabled) {
+               return THROTTLE_DISENGAGED;
+       } else {
+               return throttle_io_will_be_throttled_internal(info, NULL, NULL);
+       }
 }
-#endif
 
+/*
+ * Routine to increment I/O throttling counters maintained in the proc
+ */
 
-static int
-throttle_io_will_be_throttled_internal(int lowpri_window_msecs, void * throttle_info)
+static void
+throttle_update_proc_stats(pid_t throttling_pid, int count)
 {
-       struct _throttle_io_info_t *info = throttle_info;
-       struct timeval elapsed;
-       int elapsed_msecs;
-       int policy;
-       struct uthread  *ut;
-
-       policy = throttle_get_io_policy(&ut);
-
-       if (ut->uu_throttle_bc == FALSE && policy != IOPOL_THROTTLE)
-               return (0);
-
-       microuptime(&elapsed);
-       timevalsub(&elapsed, &info->last_normal_IO_timestamp);
-       elapsed_msecs = elapsed.tv_sec * 1000 + elapsed.tv_usec / 1000;
+       proc_t throttling_proc;
+       proc_t throttled_proc = current_proc();
 
-       if (lowpri_window_msecs == -1) // use the max waiting time
-               lowpri_window_msecs = lowpri_max_waiting_msecs;
+       /* The throttled_proc is always the current proc; so we are not concerned with refs */
+       OSAddAtomic64(count, &(throttled_proc->was_throttled));
 
-       return elapsed_msecs < lowpri_window_msecs;
+       /* The throttling pid might have exited by now */
+       throttling_proc = proc_find(throttling_pid);
+       if (throttling_proc != PROC_NULL) {
+               OSAddAtomic64(count, &(throttling_proc->did_throttle));
+               proc_rele(throttling_proc);
+       }
 }
 
-/* 
- * If we have a mount point and it has a throttle info pointer then
- * use it to do the check, otherwise use the device unit number to find
- * the correct throttle info array element.
+/*
+ * Block until woken up by the throttle timer or by a rethrottle call.
+ * As long as we hold the throttle_lock while querying the throttle tier, we're
+ * safe against seeing an old throttle tier after a rethrottle.
  */
-int
-throttle_io_will_be_throttled(int lowpri_window_msecs, mount_t mp)
-{
-       void *info;
-
-       /* Should we just return zero if no mount point */
-       if (mp == NULL)
-           info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
-       else if (mp->mnt_throttle_info == NULL)
-           info = &_throttle_io_info[mp->mnt_devbsdunit];
-       else
-           info = mp->mnt_throttle_info;
-       return throttle_io_will_be_throttled_internal(lowpri_window_msecs, info);
-}
-
 uint32_t
 throttle_lowpri_io(int sleep_amount)
 {
-       int sleep_cnt = 0;
-       int numthreads_throttling;
-       int max_try_num;
-       struct uthread *ut;
+       uthread_t ut;
        struct _throttle_io_info_t *info;
-       int max_waiting_msecs;
+       int     throttle_type = 0;
+       int     mylevel = 0;
+       int     throttling_level = THROTTLE_LEVEL_NONE;
+       int     sleep_cnt = 0;
+       uint32_t  throttle_io_period_num = 0;
+       boolean_t insert_tail = TRUE;
+       boolean_t s;
 
        ut = get_bsdthread_info(current_thread());
 
-       if ((ut->uu_lowpri_window == 0) || (ut->uu_throttle_info == NULL))
-               goto done;
+       if (ut->uu_lowpri_window == 0) {
+               return 0;
+       }
 
        info = ut->uu_throttle_info;
 
-       if (sleep_amount != 0) {
-#if CONFIG_EMBEDDED
-               max_waiting_msecs = lowpri_max_waiting_msecs;
-#else 
-               if (ut->uu_throttle_isssd == TRUE)
-                       max_waiting_msecs = lowpri_max_waiting_msecs / 100;
-               else
-                       max_waiting_msecs = lowpri_max_waiting_msecs;
-#endif
-               if (max_waiting_msecs < LOWPRI_SLEEP_INTERVAL)
-                       max_waiting_msecs = LOWPRI_SLEEP_INTERVAL;
+       if (info == NULL) {
+               ut->uu_throttle_bc = false;
+               ut->uu_lowpri_window = 0;
+               return 0;
+       }
+       lck_mtx_lock(&info->throttle_lock);
+       assert(ut->uu_on_throttlelist < THROTTLE_LEVEL_THROTTLED);
 
-               numthreads_throttling = info->numthreads_throttling + MIN(10, MAX(1, sleep_amount)) - 1;
-               max_try_num = max_waiting_msecs / LOWPRI_SLEEP_INTERVAL * MAX(1, numthreads_throttling);
+       if (sleep_amount == 0) {
+               goto done;
+       }
 
-               for (sleep_cnt = 0; sleep_cnt < max_try_num; sleep_cnt++) {
-                       if (throttle_io_will_be_throttled_internal(ut->uu_lowpri_window, info)) {
-                               if (sleep_cnt == 0) {
-                                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 97)) | DBG_FUNC_START,
-                                                             ut->uu_lowpri_window, max_try_num, numthreads_throttling, 0, 0);
-                               }
-                               IOSleep(LOWPRI_SLEEP_INTERVAL);
-                               DEBUG_ALLOC_THROTTLE_INFO("sleeping because of info = %p\n", info, info );
-                       } else {
+       if (sleep_amount == 1 && !ut->uu_throttle_bc) {
+               sleep_amount = 0;
+       }
+
+       throttle_io_period_num = info->throttle_io_period_num;
+
+       ut->uu_was_rethrottled = false;
+
+       while ((throttle_type = throttle_io_will_be_throttled_internal(info, &mylevel, &throttling_level))) {
+               if (throttle_type == THROTTLE_ENGAGED) {
+                       if (sleep_amount == 0) {
+                               break;
+                       }
+                       if (info->throttle_io_period_num < throttle_io_period_num) {
+                               break;
+                       }
+                       if ((info->throttle_io_period_num - throttle_io_period_num) >= (uint32_t)sleep_amount) {
                                break;
                        }
                }
-               if (sleep_cnt) {
-                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 97)) | DBG_FUNC_END,
-                                             ut->uu_lowpri_window, sleep_cnt, 0, 0, 0);
+               /*
+                * keep the same position in the list if "rethrottle_thread" changes our throttle level  and
+                * then puts us back to the original level before we get a chance to run
+                */
+               if (ut->uu_on_throttlelist >= THROTTLE_LEVEL_THROTTLED && ut->uu_on_throttlelist != mylevel) {
+                       /*
+                        * must have been awakened via "rethrottle_thread" (the timer pulls us off the list)
+                        * and we've changed our throttling level, so pull ourselves off of the appropriate list
+                        * and make sure we get put on the tail of the new list since we're starting anew w/r to
+                        * the throttling engine
+                        */
+                       TAILQ_REMOVE(&info->throttle_uthlist[ut->uu_on_throttlelist], ut, uu_throttlelist);
+                       ut->uu_on_throttlelist = THROTTLE_LEVEL_NONE;
+                       insert_tail = TRUE;
+               }
+               if (ut->uu_on_throttlelist < THROTTLE_LEVEL_THROTTLED) {
+                       if (throttle_add_to_list(info, ut, mylevel, insert_tail) == THROTTLE_LEVEL_END) {
+                               goto done;
+                       }
                }
-       }
-       SInt32 oldValue;
-       oldValue = OSDecrementAtomic(&info->numthreads_throttling);
+               assert(throttling_level >= THROTTLE_LEVEL_START && throttling_level <= THROTTLE_LEVEL_END);
+
+               s = ml_set_interrupts_enabled(FALSE);
+               lck_spin_lock(&ut->uu_rethrottle_lock);
+
+               /*
+                * this is the critical section w/r to our interaction
+                * with "rethrottle_thread"
+                */
+               if (ut->uu_was_rethrottled) {
+                       lck_spin_unlock(&ut->uu_rethrottle_lock);
+                       ml_set_interrupts_enabled(s);
+                       lck_mtx_yield(&info->throttle_lock);
+
+                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 103)), thread_tid(ut->uu_thread), ut->uu_on_throttlelist, 0, 0, 0);
+
+                       ut->uu_was_rethrottled = false;
+                       continue;
+               }
+               KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_THROTTLE, PROCESS_THROTTLED)) | DBG_FUNC_NONE,
+                   info->throttle_last_IO_pid[throttling_level], throttling_level, proc_selfpid(), mylevel, 0);
+
+               if (sleep_cnt == 0) {
+                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 97)) | DBG_FUNC_START,
+                           throttle_windows_msecs[mylevel], info->throttle_io_periods[mylevel], info->throttle_io_count, 0, 0);
+                       throttled_count[mylevel]++;
+               }
+               ut->uu_wmesg = "throttle_lowpri_io";
+
+               assert_wait((caddr_t)&ut->uu_on_throttlelist, THREAD_UNINT);
+
+               ut->uu_is_throttled = true;
+               lck_spin_unlock(&ut->uu_rethrottle_lock);
+               ml_set_interrupts_enabled(s);
+
+               lck_mtx_unlock(&info->throttle_lock);
+
+               thread_block(THREAD_CONTINUE_NULL);
+
+               ut->uu_wmesg = NULL;
+
+               ut->uu_is_throttled = false;
+               ut->uu_was_rethrottled = false;
+
+               lck_mtx_lock(&info->throttle_lock);
 
-       if (oldValue <= 0) {
-               panic("%s: numthreads negative", __func__);
+               sleep_cnt++;
+
+               if (sleep_amount == 0) {
+                       insert_tail = FALSE;
+               } else if (info->throttle_io_period_num < throttle_io_period_num ||
+                   (info->throttle_io_period_num - throttle_io_period_num) >= (uint32_t)sleep_amount) {
+                       insert_tail = FALSE;
+                       sleep_amount = 0;
+               }
        }
 done:
-       ut->uu_lowpri_window = 0;
-       if (ut->uu_throttle_info)
-               throttle_info_rel(ut->uu_throttle_info);
+       if (ut->uu_on_throttlelist >= THROTTLE_LEVEL_THROTTLED) {
+               TAILQ_REMOVE(&info->throttle_uthlist[ut->uu_on_throttlelist], ut, uu_throttlelist);
+               ut->uu_on_throttlelist = THROTTLE_LEVEL_NONE;
+       }
+       lck_mtx_unlock(&info->throttle_lock);
+
+       if (sleep_cnt) {
+               KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW, 97)) | DBG_FUNC_END,
+                   throttle_windows_msecs[mylevel], info->throttle_io_periods[mylevel], info->throttle_io_count, 0, 0);
+               /*
+                * We update the stats for the last pid which opened a throttle window for the throttled thread.
+                * This might not be completely accurate since the multiple throttles seen by the lower tier pid
+                * might have been caused by various higher prio pids. However, updating these stats accurately
+                * means doing a proc_find while holding the throttle lock which leads to deadlock.
+                */
+               throttle_update_proc_stats(info->throttle_last_IO_pid[throttling_level], sleep_cnt);
+       }
+
        ut->uu_throttle_info = NULL;
-       ut->uu_throttle_bc = FALSE;
+       ut->uu_throttle_bc = false;
+       ut->uu_lowpri_window = 0;
+
+       throttle_info_rel(info);
+
+       return sleep_cnt;
+}
+
+/*
+ *  returns TRUE if the throttle_lowpri_io called with the same sleep_amount would've slept
+ *  This function mimics the most of the throttle_lowpri_io checks but without actual sleeping
+ */
+int
+throttle_lowpri_io_will_be_throttled(int sleep_amount)
+{
+       if (sleep_amount == 0) {
+               return FALSE;
+       }
+
+       uthread_t ut = get_bsdthread_info(current_thread());
+       if (ut->uu_lowpri_window == 0) {
+               return FALSE;
+       }
+
+       struct _throttle_io_info_t *info = ut->uu_throttle_info;
+       if (info == NULL) {
+               return FALSE;
+       }
 
-       return (sleep_cnt * LOWPRI_SLEEP_INTERVAL);
+       lck_mtx_lock(&info->throttle_lock);
+       assert(ut->uu_on_throttlelist < THROTTLE_LEVEL_THROTTLED);
+
+       if (sleep_amount == 1 && !ut->uu_throttle_bc) {
+               sleep_amount = 0;
+       }
+
+       int result = FALSE;
+
+       int throttle_type = throttle_io_will_be_throttled_internal(info, NULL, NULL);
+       if (throttle_type > THROTTLE_DISENGAGED) {
+               result = TRUE;
+               if ((throttle_type == THROTTLE_ENGAGED) && (sleep_amount == 0)) {
+                       result = FALSE;
+               }
+       }
+
+       lck_mtx_unlock(&info->throttle_lock);
+
+       return result;
 }
 
+
 /*
  * KPI routine
  *
  * set a kernel thread's IO policy.  policy can be:
- * IOPOL_NORMAL, IOPOL_THROTTLE, IOPOL_PASSIVE
+ * IOPOL_NORMAL, IOPOL_THROTTLE, IOPOL_PASSIVE, IOPOL_UTILITY, IOPOL_STANDARD
  *
  * explanations about these policies are in the man page of setiopolicy_np
  */
-void throttle_set_thread_io_policy(int policy)
+void
+throttle_set_thread_io_policy(int policy)
 {
-#if !CONFIG_EMBEDDED
-       proc_apply_thread_selfdiskacc(policy);
-#else /* !CONFIG_EMBEDDED */
-       struct uthread *ut;
-       ut = get_bsdthread_info(current_thread());
-       ut->uu_iopol_disk = policy;
-#endif /* !CONFIG_EMBEDDED */
+       proc_set_thread_policy(current_thread(), TASK_POLICY_INTERNAL, TASK_POLICY_IOPOL, policy);
 }
 
+int
+throttle_get_thread_effective_io_policy()
+{
+       return proc_get_effective_thread_policy(current_thread(), TASK_POLICY_IO);
+}
 
-static
-void throttle_info_reset_window(struct uthread *ut)
+void
+throttle_info_reset_window(uthread_t ut)
 {
        struct _throttle_io_info_t *info;
 
-       info = ut->uu_throttle_info;
+       if (ut == NULL) {
+               ut = get_bsdthread_info(current_thread());
+       }
 
-       OSDecrementAtomic(&info->numthreads_throttling);
-       throttle_info_rel(info);
-       ut->uu_throttle_info = NULL;
-       ut->uu_lowpri_window = 0;
+       if ((info = ut->uu_throttle_info)) {
+               throttle_info_rel(info);
+
+               ut->uu_throttle_info = NULL;
+               ut->uu_lowpri_window = 0;
+               ut->uu_throttle_bc = false;
+       }
 }
 
 static
-void throttle_info_set_initial_window(struct uthread *ut, struct _throttle_io_info_t *info, boolean_t isssd, boolean_t BC_throttle)
+void
+throttle_info_set_initial_window(uthread_t ut, struct _throttle_io_info_t *info, boolean_t BC_throttle, boolean_t isssd)
 {
-       SInt32 oldValue;
+       if (lowpri_throttle_enabled == 0 || info->throttle_disabled) {
+               return;
+       }
 
-       ut->uu_throttle_info = info;
-       throttle_info_ref(info);
-       DEBUG_ALLOC_THROTTLE_INFO("updating info = %p\n", info, info );
+       if (info->throttle_io_periods == 0) {
+               throttle_init_throttle_period(info, isssd);
+       }
+       if (ut->uu_throttle_info == NULL) {
+               ut->uu_throttle_info = info;
+               throttle_info_ref(info);
+               DEBUG_ALLOC_THROTTLE_INFO("updating info = %p\n", info, info );
+
+               ut->uu_lowpri_window = 1;
+               ut->uu_throttle_bc = BC_throttle;
+       }
+}
+
+/*
+ * Update inflight IO count and throttling window
+ * Should be called when an IO is done
+ *
+ * Only affects IO that was sent through spec_strategy
+ */
+void
+throttle_info_end_io(buf_t bp)
+{
+       mount_t mp;
+       struct bufattr *bap;
+       struct _throttle_io_info_t *info;
+       int io_tier;
+
+       bap = &bp->b_attr;
+       if (!ISSET(bap->ba_flags, BA_STRATEGY_TRACKED_IO)) {
+               return;
+       }
+       CLR(bap->ba_flags, BA_STRATEGY_TRACKED_IO);
+
+       mp = buf_vnode(bp)->v_mount;
+       if (mp != NULL) {
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       }
 
-       oldValue = OSIncrementAtomic(&info->numthreads_throttling);
-       if (oldValue < 0) {
-               panic("%s: numthreads negative", __func__);
+       io_tier = GET_BUFATTR_IO_TIER(bap);
+       if (ISSET(bap->ba_flags, BA_IO_TIER_UPGRADE)) {
+               io_tier--;
        }
-       ut->uu_lowpri_window = lowpri_IO_initial_window_msecs;
-       ut->uu_lowpri_window += lowpri_IO_window_msecs_inc * oldValue;
-       ut->uu_throttle_isssd = isssd;
-       ut->uu_throttle_bc = BC_throttle;
+
+       throttle_info_end_io_internal(info, io_tier);
 }
 
+/*
+ * Decrement inflight count initially incremented by throttle_info_update_internal
+ */
+static
+void
+throttle_info_end_io_internal(struct _throttle_io_info_t *info, int throttle_level)
+{
+       if (throttle_level == THROTTLE_LEVEL_NONE) {
+               return;
+       }
+
+       microuptime(&info->throttle_window_start_timestamp[throttle_level]);
+       OSDecrementAtomic(&info->throttle_inflight_count[throttle_level]);
+       assert(info->throttle_inflight_count[throttle_level] >= 0);
+}
 
+/*
+ * If inflight is TRUE and bap is NULL then the caller is responsible for calling
+ * throttle_info_end_io_internal to avoid leaking in-flight I/O.
+ */
 static
-void throttle_info_update_internal(void *throttle_info, int flags, boolean_t isssd)
+int
+throttle_info_update_internal(struct _throttle_io_info_t *info, uthread_t ut, int flags, boolean_t isssd, boolean_t inflight, struct bufattr *bap)
+{
+       int     thread_throttle_level;
+
+       if (lowpri_throttle_enabled == 0 || info->throttle_disabled) {
+               return THROTTLE_LEVEL_NONE;
+       }
+
+       if (ut == NULL) {
+               ut = get_bsdthread_info(current_thread());
+       }
+
+       if (bap && inflight && !ut->uu_throttle_bc) {
+               thread_throttle_level = GET_BUFATTR_IO_TIER(bap);
+               if (ISSET(bap->ba_flags, BA_IO_TIER_UPGRADE)) {
+                       thread_throttle_level--;
+               }
+       } else {
+               thread_throttle_level = throttle_get_thread_throttle_level(ut);
+       }
+
+       if (thread_throttle_level != THROTTLE_LEVEL_NONE) {
+               if (!ISSET(flags, B_PASSIVE)) {
+                       info->throttle_last_IO_pid[thread_throttle_level] = proc_selfpid();
+                       if (inflight && !ut->uu_throttle_bc) {
+                               if (NULL != bap) {
+                                       SET(bap->ba_flags, BA_STRATEGY_TRACKED_IO);
+                               }
+                               OSIncrementAtomic(&info->throttle_inflight_count[thread_throttle_level]);
+                       } else {
+                               microuptime(&info->throttle_window_start_timestamp[thread_throttle_level]);
+                       }
+                       KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_THROTTLE, OPEN_THROTTLE_WINDOW)) | DBG_FUNC_NONE,
+                           current_proc()->p_pid, thread_throttle_level, 0, 0, 0);
+               }
+               microuptime(&info->throttle_last_IO_timestamp[thread_throttle_level]);
+       }
+
+
+       if (thread_throttle_level >= THROTTLE_LEVEL_THROTTLED) {
+               /*
+                * I'd really like to do the IOSleep here, but
+                * we may be holding all kinds of filesystem related locks
+                * and the pages for this I/O marked 'busy'...
+                * we don't want to cause a normal task to block on
+                * one of these locks while we're throttling a task marked
+                * for low priority I/O... we'll mark the uthread and
+                * do the delay just before we return from the system
+                * call that triggered this I/O or from vnode_pagein
+                */
+               OSAddAtomic(1, &info->throttle_io_count);
+
+               throttle_info_set_initial_window(ut, info, FALSE, isssd);
+       }
+
+       return thread_throttle_level;
+}
+
+void *
+throttle_info_update_by_mount(mount_t mp)
+{
+       struct _throttle_io_info_t *info;
+       uthread_t ut;
+       boolean_t isssd = FALSE;
+
+       ut = get_bsdthread_info(current_thread());
+
+       if (mp != NULL) {
+               if (disk_conditioner_mount_is_ssd(mp)) {
+                       isssd = TRUE;
+               }
+               info = &_throttle_io_info[mp->mnt_devbsdunit];
+       } else {
+               info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       }
+
+       if (!ut->uu_lowpri_window) {
+               throttle_info_set_initial_window(ut, info, FALSE, isssd);
+       }
+
+       return info;
+}
+
+
+/*
+ * KPI routine
+ *
+ * this is usually called before every I/O, used for throttled I/O
+ * book keeping.  This routine has low overhead and does not sleep
+ */
+void
+throttle_info_update(void *throttle_info, int flags)
+{
+       if (throttle_info) {
+               throttle_info_update_internal(throttle_info, NULL, flags, FALSE, FALSE, NULL);
+       }
+}
+
+/*
+ * KPI routine
+ *
+ * this is usually called before every I/O, used for throttled I/O
+ * book keeping.  This routine has low overhead and does not sleep
+ */
+void
+throttle_info_update_by_mask(void *throttle_info_handle, int flags)
+{
+       void *throttle_info = throttle_info_handle;
+
+       /*
+        * for now we only use the lowest bit of the throttle mask, so the
+        * handle is the same as the throttle_info.  Later if we store a
+        * set of throttle infos in the handle, we will want to loop through
+        * them and call throttle_info_update in a loop
+        */
+       throttle_info_update(throttle_info, flags);
+}
+/*
+ * KPI routine
+ *
+ * This routine marks the throttle info as disabled. Used for mount points which
+ * support I/O scheduling.
+ */
+
+void
+throttle_info_disable_throttle(int devno, boolean_t isfusion)
+{
+       struct _throttle_io_info_t *info;
+
+       if (devno < 0 || devno >= LOWPRI_MAX_NUM_DEV) {
+               panic("Illegal devno (%d) passed into throttle_info_disable_throttle()", devno);
+       }
+
+       info = &_throttle_io_info[devno];
+       // don't disable software throttling on devices that are part of a fusion device
+       // and override the software throttle periods to use HDD periods
+       if (isfusion) {
+               info->throttle_is_fusion_with_priority = isfusion;
+               throttle_init_throttle_period(info, FALSE);
+       }
+       info->throttle_disabled = !info->throttle_is_fusion_with_priority;
+       return;
+}
+
+
+/*
+ * KPI routine (private)
+ * Called to determine if this IO is being throttled to this level so that it can be treated specially
+ */
+int
+throttle_info_io_will_be_throttled(void * throttle_info, int policy)
 {
        struct _throttle_io_info_t *info = throttle_info;
-       struct uthread  *ut;
-       int policy;
-       int is_throttleable_io = 0;
-       int is_passive_io = 0;
-
-       if (!lowpri_IO_initial_window_msecs || (info == NULL))
-               return;
-       policy = throttle_get_io_policy(&ut);
+       struct timeval elapsed;
+       uint64_t elapsed_msecs;
+       int     throttle_level;
+       int     thread_throttle_level;
 
        switch (policy) {
-       case IOPOL_DEFAULT:
-       case IOPOL_NORMAL:
-               break;
        case IOPOL_THROTTLE:
-               is_throttleable_io = 1;
+               thread_throttle_level = THROTTLE_LEVEL_TIER3;
                break;
-       case IOPOL_PASSIVE:
-               is_passive_io = 1;
+       case IOPOL_UTILITY:
+               thread_throttle_level = THROTTLE_LEVEL_TIER2;
+               break;
+       case IOPOL_STANDARD:
+               thread_throttle_level = THROTTLE_LEVEL_TIER1;
                break;
        default:
-               printf("unknown I/O policy %d", policy);
+               thread_throttle_level = THROTTLE_LEVEL_TIER0;
                break;
        }
+       for (throttle_level = THROTTLE_LEVEL_START; throttle_level < thread_throttle_level; throttle_level++) {
+               if (info->throttle_inflight_count[throttle_level]) {
+                       break;
+               }
 
-       if (!is_throttleable_io && ISSET(flags, B_PASSIVE))
-               is_passive_io |= 1;
+               microuptime(&elapsed);
+               timevalsub(&elapsed, &info->throttle_window_start_timestamp[throttle_level]);
+               elapsed_msecs = (uint64_t)elapsed.tv_sec * (uint64_t)1000 + (elapsed.tv_usec / 1000);
 
-       if (!is_throttleable_io) {
-               if (!is_passive_io){
-                       microuptime(&info->last_normal_IO_timestamp);
+               if (elapsed_msecs < (uint64_t)throttle_windows_msecs[thread_throttle_level]) {
+                       break;
                }
-       } else if (ut) {
+       }
+       if (throttle_level >= thread_throttle_level) {
                /*
-                * I'd really like to do the IOSleep here, but
-                * we may be holding all kinds of filesystem related locks
-                * and the pages for this I/O marked 'busy'...
-                * we don't want to cause a normal task to block on
-                * one of these locks while we're throttling a task marked
-                * for low priority I/O... we'll mark the uthread and
-                * do the delay just before we return from the system
-                * call that triggered this I/O or from vnode_pagein
+                * we're beyond all of the throttle windows
+                * so go ahead and treat as normal I/O
                 */
-               if (ut->uu_lowpri_window == 0)
-                       throttle_info_set_initial_window(ut, info, isssd, FALSE);
-               else {
-                       /* The thread sends I/Os to different devices within the same system call */
-                       if (ut->uu_throttle_info != info) {
-                               struct _throttle_io_info_t *old_info = ut->uu_throttle_info;
-
-                               // keep track of the numthreads in the right device
-                               OSDecrementAtomic(&old_info->numthreads_throttling);
-                               OSIncrementAtomic(&info->numthreads_throttling);
-
-                               DEBUG_ALLOC_THROTTLE_INFO("switching from info = %p\n", old_info, old_info );
-                               DEBUG_ALLOC_THROTTLE_INFO("switching to info = %p\n", info, info );
-                               /* This thread no longer needs a reference on that throttle info */
-                               throttle_info_rel(ut->uu_throttle_info);
-                               ut->uu_throttle_info = info;
-                               /* Need to take a reference on this throttle info */
-                               throttle_info_ref(ut->uu_throttle_info);
-                       }
-                       int numthreads = MAX(1, info->numthreads_throttling);
-                       ut->uu_lowpri_window += lowpri_IO_window_msecs_inc * numthreads;
-                       if (ut->uu_lowpri_window > lowpri_max_window_msecs * numthreads)
-                               ut->uu_lowpri_window = lowpri_max_window_msecs * numthreads;
-
-                       if (isssd == FALSE) {
-                               /*
-                                * we're here because we've actually issued I/Os to different devices...
-                                * if at least one of them was a non SSD, then thottle the thread
-                                * using the policy for non SSDs
-                                */
-                               ut->uu_throttle_isssd = FALSE;
-                       }
-               }
+               return THROTTLE_DISENGAGED;
        }
+       /*
+        * we're in the throttle window
+        */
+       return THROTTLE_ENGAGED;
 }
 
-/*
- * KPI routine
- *
- * this is usually called before every I/O, used for throttled I/O
- * book keeping.  This routine has low overhead and does not sleep
- */
-void throttle_info_update(void *throttle_info, int flags)
+int
+throttle_lowpri_window(void)
 {
-       throttle_info_update_internal(throttle_info, flags, FALSE);
+       struct uthread *ut = get_bsdthread_info(current_thread());
+       return ut->uu_lowpri_window;
 }
 
-/*
- * KPI routine
- *
- * this is usually called before every I/O, used for throttled I/O
- * book keeping.  This routine has low overhead and does not sleep
- */
-void throttle_info_update_by_mask(void *throttle_info_handle, int flags)
-{
-       void *throttle_info = throttle_info_handle;
-       /* for now we only use the lowest bit of the throttle mask, so the
-        * handle is the same as the throttle_info.  Later if we store a
-        * set of throttle infos in the handle, we will want to loop through
-        * them and call throttle_info_update in a loop
-        */
-       throttle_info_update(throttle_info, flags);
-}
 
-extern int ignore_is_ssd;
+#if CONFIG_IOSCHED
+int upl_get_cached_tier(void *);
+#endif
 
 int
 spec_strategy(struct vnop_strategy_args *ap)
 {
-        buf_t  bp;
-       int     bflags;
-       int     policy;
-       dev_t   bdev;
+       buf_t   bp;
+       int     bflags;
+       int     io_tier;
+       int     passive;
+       dev_t   bdev;
        uthread_t ut;
        mount_t mp;
-       int strategy_ret;
+       struct  bufattr *bap;
+       int     strategy_ret;
        struct _throttle_io_info_t *throttle_info;
        boolean_t isssd = FALSE;
+       boolean_t inflight = FALSE;
+       boolean_t upgrade = FALSE;
+       int code = 0;
+
+#if !CONFIG_EMBEDDED
+       proc_t curproc = current_proc();
+#endif /* !CONFIG_EMBEDDED */
 
-        bp = ap->a_bp;
+       bp = ap->a_bp;
        bdev = buf_device(bp);
        mp = buf_vnode(bp)->v_mount;
+       bap = &bp->b_attr;
+
+#if CONFIG_IOSCHED
+       if (bp->b_flags & B_CLUSTER) {
+               io_tier = upl_get_cached_tier(bp->b_upl);
+
+               if (io_tier == -1) {
+                       io_tier = throttle_get_io_policy(&ut);
+               }
+#if DEVELOPMENT || DEBUG
+               else {
+                       int my_io_tier = throttle_get_io_policy(&ut);
+
+                       if (io_tier != my_io_tier) {
+                               KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_THROTTLE, IO_TIER_UPL_MISMATCH)) | DBG_FUNC_NONE, buf_kernel_addrperm_addr(bp), my_io_tier, io_tier, 0, 0);
+                       }
+               }
+#endif
+       } else {
+               io_tier = throttle_get_io_policy(&ut);
+       }
+#else
+       io_tier = throttle_get_io_policy(&ut);
+#endif
+       passive = throttle_get_passive_io_policy(&ut);
+
+       /*
+        * Mark if the I/O was upgraded by throttle_get_thread_throttle_level
+        * while preserving the original issued tier (throttle_get_io_policy
+        * does not return upgraded tiers)
+        */
+       if (mp && io_tier > throttle_get_thread_throttle_level_internal(ut, io_tier)) {
+#if CONFIG_IOSCHED
+               if (!(mp->mnt_ioflags & MNT_IOFLAGS_IOSCHED_SUPPORTED)) {
+                       upgrade = TRUE;
+               }
+#else /* CONFIG_IOSCHED */
+               upgrade = TRUE;
+#endif /* CONFIG_IOSCHED */
+       }
+
+       if (bp->b_flags & B_META) {
+               bap->ba_flags |= BA_META;
+       }
+
+#if CONFIG_IOSCHED
+       /*
+        * For I/O Scheduling, we currently do not have a way to track and expedite metadata I/Os.
+        * To ensure we dont get into priority inversions due to metadata I/Os, we use the following rules:
+        * For metadata reads, ceil all I/Os to IOSCHED_METADATA_TIER & mark them passive if the I/O tier was upgraded
+        * For metadata writes, unconditionally mark them as IOSCHED_METADATA_TIER and passive
+        */
+       if (bap->ba_flags & BA_META) {
+               if ((mp && (mp->mnt_ioflags & MNT_IOFLAGS_IOSCHED_SUPPORTED)) || (bap->ba_flags & BA_IO_SCHEDULED)) {
+                       if (bp->b_flags & B_READ) {
+                               if (io_tier > IOSCHED_METADATA_TIER) {
+                                       io_tier = IOSCHED_METADATA_TIER;
+                                       passive = 1;
+                               }
+                       } else {
+                               io_tier = IOSCHED_METADATA_TIER;
+                               passive = 1;
+                       }
+               }
+       }
+#endif /* CONFIG_IOSCHED */
 
-       policy = throttle_get_io_policy(&ut);
+       SET_BUFATTR_IO_TIER(bap, io_tier);
 
-       if (policy == IOPOL_THROTTLE) {
-               bp->b_flags |= B_THROTTLED_IO;
-               bp->b_attr.ba_flags |= BA_THROTTLED_IO;
-               bp->b_flags &= ~B_PASSIVE;
-       } else if (policy == IOPOL_PASSIVE)
+       if (passive) {
                bp->b_flags |= B_PASSIVE;
+               bap->ba_flags |= BA_PASSIVE;
+       }
+
+#if !CONFIG_EMBEDDED
+       if ((curproc != NULL) && ((curproc->p_flag & P_DELAYIDLESLEEP) == P_DELAYIDLESLEEP)) {
+               bap->ba_flags |= BA_DELAYIDLESLEEP;
+       }
+#endif /* !CONFIG_EMBEDDED */
 
        bflags = bp->b_flags;
 
-        if (kdebug_enable) {
-               int    code = 0;
+       if (((bflags & B_READ) == 0) && ((bflags & B_ASYNC) == 0)) {
+               bufattr_markquickcomplete(bap);
+       }
+
+       if (bflags & B_READ) {
+               code |= DKIO_READ;
+       }
+       if (bflags & B_ASYNC) {
+               code |= DKIO_ASYNC;
+       }
+
+       if (bap->ba_flags & BA_META) {
+               code |= DKIO_META;
+       } else if (bflags & B_PAGEIO) {
+               code |= DKIO_PAGING;
+       }
+
+       if (io_tier != 0) {
+               code |= DKIO_THROTTLE;
+       }
+
+       code |= ((io_tier << DKIO_TIER_SHIFT) & DKIO_TIER_MASK);
+
+       if (bflags & B_PASSIVE) {
+               code |= DKIO_PASSIVE;
+       }
 
-               if (bflags & B_READ)
-                       code |= DKIO_READ;
-               if (bflags & B_ASYNC)
-                       code |= DKIO_ASYNC;
+       if (bap->ba_flags & BA_NOCACHE) {
+               code |= DKIO_NOCACHE;
+       }
 
-               if (bflags & B_META)
-                       code |= DKIO_META;
-               else if (bflags & B_PAGEIO)
-                       code |= DKIO_PAGING;
+       if (upgrade) {
+               code |= DKIO_TIER_UPGRADE;
+               SET(bap->ba_flags, BA_IO_TIER_UPGRADE);
+       }
 
-               if (bflags & B_THROTTLED_IO)
-                       code |= DKIO_THROTTLE;
-               else if (bflags & B_PASSIVE)
-                       code |= DKIO_PASSIVE;
+       if (kdebug_enable) {
+               KERNEL_DEBUG_CONSTANT_IST(KDEBUG_COMMON, FSDBG_CODE(DBG_DKRW, code) | DBG_FUNC_NONE,
+                   buf_kernel_addrperm_addr(bp), bdev, buf_blkno(bp), buf_count(bp), 0);
+       }
 
-               KERNEL_DEBUG_CONSTANT(FSDBG_CODE(DBG_DKRW, code) | DBG_FUNC_NONE,
-                                     bp, bdev, (int)buf_blkno(bp), buf_count(bp), 0);
-        }
-       if (((bflags & (B_IOSTREAMING | B_PAGEIO | B_READ)) == (B_PAGEIO | B_READ)) &&
-           mp && (mp->mnt_kern_flag & MNTK_ROOTDEV))
-               hard_throttle_on_root = 1;
+       thread_update_io_stats(current_thread(), buf_count(bp), code);
 
        if (mp != NULL) {
-               if ((mp->mnt_kern_flag & MNTK_SSD) && !ignore_is_ssd)
+               if (disk_conditioner_mount_is_ssd(mp)) {
                        isssd = TRUE;
+               }
+               /*
+                * Partially initialized mounts don't have a final devbsdunit and should not be tracked.
+                * Verify that devbsdunit is initialized (non-zero) or that 0 is the correct initialized value
+                * (mnt_throttle_mask is initialized and num_trailing_0 would be 0)
+                */
+               if (mp->mnt_devbsdunit || (mp->mnt_throttle_mask != LOWPRI_MAX_NUM_DEV - 1 && mp->mnt_throttle_mask & 0x1)) {
+                       inflight = TRUE;
+               }
                throttle_info = &_throttle_io_info[mp->mnt_devbsdunit];
-       } else
+       } else {
                throttle_info = &_throttle_io_info[LOWPRI_MAX_NUM_DEV - 1];
+       }
 
-       throttle_info_update_internal(throttle_info, bflags, isssd);
+       throttle_info_update_internal(throttle_info, ut, bflags, isssd, inflight, bap);
 
        if ((bflags & B_READ) == 0) {
-               microuptime(&throttle_info->last_IO_timestamp);
+               microuptime(&throttle_info->throttle_last_write_timestamp);
+
                if (mp) {
+                       mp->mnt_last_write_issued_timestamp = throttle_info->throttle_last_write_timestamp;
                        INCR_PENDING_IO(buf_count(bp), mp->mnt_pending_write_size);
                }
        } else if (mp) {
@@ -1331,32 +2612,36 @@ spec_strategy(struct vnop_strategy_args *ap)
         * the boot cache too often.
         *
         * Note that typical strategy routines are defined with
-        * a void return so we'll get garbage here. In the 
+        * a void return so we'll get garbage here. In the
         * unlikely case the garbage matches our special return
         * value, it's not a big deal since we're only adjusting
         * the throttling delay.
-        */
+        */
 #define IO_SATISFIED_BY_CACHE  ((int)0xcafefeed)
 #define IO_SHOULD_BE_THROTTLED ((int)0xcafebeef)
-       typedef int strategy_fcn_ret_t(struct buf *bp);
-       
+       typedef int strategy_fcn_ret_t(struct buf *bp);
+
        strategy_ret = (*(strategy_fcn_ret_t*)bdevsw[major(bdev)].d_strategy)(bp);
-       
-       if ((IO_SATISFIED_BY_CACHE == strategy_ret) && (ut->uu_lowpri_window != 0) && (ut->uu_throttle_info != NULL)) {
+
+       // disk conditioner needs to track when this I/O actually starts
+       // which means track it after `strategy` which may include delays
+       // from inflight I/Os
+       microuptime(&bp->b_timestamp_tv);
+
+       if (IO_SATISFIED_BY_CACHE == strategy_ret) {
                /*
                 * If this was a throttled IO satisfied by the boot cache,
                 * don't delay the thread.
                 */
                throttle_info_reset_window(ut);
-
-       } else if ((IO_SHOULD_BE_THROTTLED == strategy_ret) && (ut->uu_lowpri_window == 0) && (ut->uu_throttle_info == NULL)) {
+       } else if (IO_SHOULD_BE_THROTTLED == strategy_ret) {
                /*
                 * If the boot cache indicates this IO should be throttled,
                 * delay the thread.
                 */
-               throttle_info_set_initial_window(ut, throttle_info, isssd, TRUE);
+               throttle_info_set_initial_window(ut, throttle_info, TRUE, isssd);
        }
-       return (0);
+       return 0;
 }
 
 
@@ -1366,7 +2651,7 @@ spec_strategy(struct vnop_strategy_args *ap)
 int
 spec_blockmap(__unused struct vnop_blockmap_args *ap)
 {
-       return (ENOTSUP);
+       return ENOTSUP;
 }
 
 
@@ -1382,10 +2667,8 @@ spec_close(struct vnop_close_args *ap)
        int flags = ap->a_fflag;
        struct proc *p = vfs_context_proc(ap->a_context);
        struct session *sessp;
-       int do_rele = 0;
 
        switch (vp->v_type) {
-
        case VCHR:
                /*
                 * Hack: a tty device that is a controlling terminal
@@ -1394,46 +2677,52 @@ spec_close(struct vnop_close_args *ap)
                 * a controlling terminal, unless it is the closing
                 * process' controlling terminal.  In that case,
                 * if the reference count is 1 (this is the very
-            * last close)
+                * last close)
                 */
                sessp = proc_session(p);
+               devsw_lock(dev, S_IFCHR);
                if (sessp != SESSION_NULL) {
-                       if ((vcount(vp) == 1) && 
-                               (vp == sessp->s_ttyvp)) {
+                       if (vp == sessp->s_ttyvp && vcount(vp) == 1) {
+                               struct tty *tp = TTY_NULL;
 
+                               devsw_unlock(dev, S_IFCHR);
                                session_lock(sessp);
                                if (vp == sessp->s_ttyvp) {
+                                       tp = SESSION_TP(sessp);
                                        sessp->s_ttyvp = NULL;
                                        sessp->s_ttyvid = 0;
                                        sessp->s_ttyp = TTY_NULL;
                                        sessp->s_ttypgrpid = NO_PID;
-                                       do_rele = 1;
-                               } 
+                               }
                                session_unlock(sessp);
 
-                               if (do_rele) {
-                                       vnode_rele(vp);
+                               if (tp != TTY_NULL) {
+                                       /*
+                                        * We may have won a race with a proc_exit
+                                        * of the session leader, the winner
+                                        * clears the flag (even if not set)
+                                        */
+                                       tty_lock(tp);
+                                       ttyclrpgrphup(tp);
+                                       tty_unlock(tp);
+
+                                       ttyfree(tp);
                                }
+                               devsw_lock(dev, S_IFCHR);
                        }
                        session_rele(sessp);
                }
 
-               devsw_lock(dev, S_IFCHR);
-
-               vp->v_specinfo->si_opencount--;
-
-               if (vp->v_specinfo->si_opencount < 0) {
-                       panic("Negative open count?");
+               if (--vp->v_specinfo->si_opencount < 0) {
+                       panic("negative open count (c, %u, %u)", major(dev), minor(dev));
                }
+
                /*
                 * close on last reference or on vnode revoke call
                 */
-               if ((vcount(vp) > 0) && ((flags & IO_REVOKE) == 0)) {
-                       devsw_unlock(dev, S_IFCHR);
-                       return (0);
-               }       
-               
-               error = cdevsw[major(dev)].d_close(dev, flags, S_IFCHR, p);
+               if (vcount(vp) == 0 || (flags & IO_REVOKE) != 0) {
+                       error = cdevsw[major(dev)].d_close(dev, flags, S_IFCHR, p);
+               }
 
                devsw_unlock(dev, S_IFCHR);
                break;
@@ -1447,7 +2736,7 @@ spec_close(struct vnop_close_args *ap)
                if (vcount(vp) > 1) {
                        vp->v_specinfo->si_opencount--;
                        devsw_unlock(dev, S_IFBLK);
-                       return (0);
+                       return 0;
                }
                devsw_unlock(dev, S_IFBLK);
 
@@ -1456,34 +2745,31 @@ spec_close(struct vnop_close_args *ap)
                 * we must invalidate any in core blocks, so that
                 * we can, for instance, change floppy disks.
                 */
-               if ((error = spec_fsync_internal(vp, MNT_WAIT, ap->a_context)))
-                       return (error);
+               if ((error = spec_fsync_internal(vp, MNT_WAIT, ap->a_context))) {
+                       return error;
+               }
 
                error = buf_invalidateblks(vp, BUF_WRITE_DATA, 0, 0);
-               if (error)
-                       return (error);
+               if (error) {
+                       return error;
+               }
 
                devsw_lock(dev, S_IFBLK);
 
-               vp->v_specinfo->si_opencount--;
-               
-               if (vp->v_specinfo->si_opencount < 0) {
-                       panic("Negative open count?");
+               if (--vp->v_specinfo->si_opencount < 0) {
+                       panic("negative open count (b, %u, %u)", major(dev), minor(dev));
                }
 
-               if (vcount(vp) > 0) {
-                       devsw_unlock(dev, S_IFBLK);
-                       return (0);
+               if (vcount(vp) == 0) {
+                       error = bdevsw[major(dev)].d_close(dev, flags, S_IFBLK, p);
                }
 
-               error = bdevsw[major(dev)].d_close(dev, flags, S_IFBLK, p);
-
                devsw_unlock(dev, S_IFBLK);
                break;
 
        default:
                panic("spec_close: not special");
-               return(EBADF);
+               return EBADF;
        }
 
        return error;
@@ -1495,28 +2781,27 @@ spec_close(struct vnop_close_args *ap)
 int
 spec_pathconf(struct vnop_pathconf_args *ap)
 {
-
        switch (ap->a_name) {
        case _PC_LINK_MAX:
                *ap->a_retval = LINK_MAX;
-               return (0);
+               return 0;
        case _PC_MAX_CANON:
                *ap->a_retval = MAX_CANON;
-               return (0);
+               return 0;
        case _PC_MAX_INPUT:
                *ap->a_retval = MAX_INPUT;
-               return (0);
+               return 0;
        case _PC_PIPE_BUF:
                *ap->a_retval = PIPE_BUF;
-               return (0);
+               return 0;
        case _PC_CHOWN_RESTRICTED:
-               *ap->a_retval = 200112;         /* _POSIX_CHOWN_RESTRICTED */
-               return (0);
+               *ap->a_retval = 200112;         /* _POSIX_CHOWN_RESTRICTED */
+               return 0;
        case _PC_VDISABLE:
                *ap->a_retval = _POSIX_VDISABLE;
-               return (0);
+               return 0;
        default:
-               return (EINVAL);
+               return EINVAL;
        }
        /* NOTREACHED */
 }
@@ -1527,8 +2812,7 @@ spec_pathconf(struct vnop_pathconf_args *ap)
 int
 spec_ebadf(__unused void *dummy)
 {
-
-       return (EBADF);
+       return EBADF;
 }
 
 /* Blktooff derives file offset from logical block number */
@@ -1540,19 +2824,19 @@ spec_blktooff(struct vnop_blktooff_args *ap)
        switch (vp->v_type) {
        case VCHR:
                *ap->a_offset = (off_t)-1; /* failure */
-               return (ENOTSUP);
+               return ENOTSUP;
 
        case VBLK:
                printf("spec_blktooff: not implemented for VBLK\n");
                *ap->a_offset = (off_t)-1; /* failure */
-               return (ENOTSUP);
+               return ENOTSUP;
 
        default:
                panic("spec_blktooff type");
        }
        /* NOTREACHED */
 
-       return (0);
+       return 0;
 }
 
 /* Offtoblk derives logical block number from file offset */
@@ -1564,50 +2848,194 @@ spec_offtoblk(struct vnop_offtoblk_args *ap)
        switch (vp->v_type) {
        case VCHR:
                *ap->a_lblkno = (daddr64_t)-1; /* failure */
-               return (ENOTSUP);
+               return ENOTSUP;
 
        case VBLK:
                printf("spec_offtoblk: not implemented for VBLK\n");
                *ap->a_lblkno = (daddr64_t)-1; /* failure */
-               return (ENOTSUP);
+               return ENOTSUP;
 
        default:
                panic("spec_offtoblk type");
        }
        /* NOTREACHED */
 
-       return (0);
+       return 0;
 }
 
 static void filt_specdetach(struct knote *kn);
-static int filt_spec(struct knote *kn, long hint);
-static unsigned filt_specpeek(struct knote *kn);
-
-struct filterops spec_filtops = {
-       .f_isfd         = 1,
-        .f_attach      = filt_specattach,
-        .f_detach      = filt_specdetach,
-        .f_event       = filt_spec,
-       .f_peek         = filt_specpeek
+static int filt_specevent(struct knote *kn, long hint);
+static int filt_spectouch(struct knote *kn, struct kevent_qos_s *kev);
+static int filt_specprocess(struct knote *kn, struct kevent_qos_s *kev);
+static int filt_specpeek(struct knote *kn);
+
+SECURITY_READ_ONLY_EARLY(struct filterops) spec_filtops = {
+       .f_isfd    = 1,
+       .f_attach  = filt_specattach,
+       .f_detach  = filt_specdetach,
+       .f_event   = filt_specevent,
+       .f_touch   = filt_spectouch,
+       .f_process = filt_specprocess,
+       .f_peek    = filt_specpeek
 };
 
+
+/*
+ * Given a waitq that is assumed to be embedded within a selinfo structure,
+ * return the containing selinfo structure. While 'wq' is not really a queue
+ * element, this macro simply does the offset_of calculation to get back to a
+ * containing struct given the struct type and member name.
+ */
+#define selinfo_from_waitq(wq) \
+       qe_element((wq), struct selinfo, si_waitq)
+
 static int
-filter_to_seltype(int16_t filter)
+spec_knote_select_and_link(struct knote *kn)
 {
-       switch (filter) {
-       case EVFILT_READ: 
-               return FREAD;
-       case EVFILT_WRITE:
-               return FWRITE;
-               break;
-       default:
-               panic("filt_to_seltype(): invalid filter %d\n", filter);
+       uthread_t uth;
+       vfs_context_t ctx;
+       vnode_t vp;
+       struct waitq_set *old_wqs;
+       uint64_t rsvd, rsvd_arg;
+       uint64_t *rlptr = NULL;
+       struct selinfo *si = NULL;
+       int selres = 0;
+
+       uth = get_bsdthread_info(current_thread());
+
+       ctx = vfs_context_current();
+       vp = (vnode_t)kn->kn_fp->f_fglob->fg_data;
+
+       int error = vnode_getwithvid(vp, vnode_vid(vp));
+       if (error != 0) {
+               knote_set_error(kn, ENOENT);
                return 0;
        }
+
+       /*
+        * This function may be called many times to link or re-link the
+        * underlying vnode to the kqueue.  If we've already linked the two,
+        * we will have a valid kn_hook_waitqid which ties us to the underlying
+        * device's waitq via a the waitq's prepost table object. However,
+        * devices can abort any select action by calling selthreadclear().
+        * This is OK because the table object will be invalidated by the
+        * driver (through a call to selthreadclear), so any attempt to access
+        * the associated waitq will fail because the table object is invalid.
+        *
+        * Even if we've already registered, we need to pass a pointer
+        * to a reserved link structure. Otherwise, selrecord() will
+        * infer that we're in the second pass of select() and won't
+        * actually do anything!
+        */
+       rsvd = rsvd_arg = waitq_link_reserve(NULL);
+       rlptr = (void *)&rsvd_arg;
+
+       /*
+        * Trick selrecord() into hooking kqueue's wait queue set into the device's
+        * selinfo wait queue.
+        */
+       old_wqs = uth->uu_wqset;
+       uth->uu_wqset = &(knote_get_kq(kn)->kq_wqs);
+
+       /*
+        * Be sure that the waitq set is linked
+        * before calling select to avoid possible
+        * allocation under spinlocks.
+        */
+       waitq_set_lazy_init_link(uth->uu_wqset);
+
+       /*
+        * Now these are the laws of VNOP_SELECT, as old and as true as the sky,
+        * And the device that shall keep it may prosper, but the device that shall
+        * break it must receive ENODEV:
+        *
+        * 1. Take a lock to protect against other selects on the same vnode.
+        * 2. Return 1 if data is ready to be read.
+        * 3. Return 0 and call `selrecord` on a handy `selinfo` structure if there
+        *    is no data.
+        * 4. Call `selwakeup` when the vnode has an active `selrecord` and data
+        *    can be read or written (depending on the seltype).
+        * 5. If there's a `selrecord` and no corresponding `selwakeup`, but the
+        *    vnode is going away, call `selthreadclear`.
+        */
+       selres = VNOP_SELECT(vp, knote_get_seltype(kn), 0, rlptr, ctx);
+       uth->uu_wqset = old_wqs;
+
+       /*
+        * Make sure to cleanup the reserved link - this guards against
+        * drivers that may not actually call selrecord().
+        */
+       waitq_link_release(rsvd);
+       if (rsvd != rsvd_arg) {
+               /* The driver / handler called selrecord() */
+               struct waitq *wq;
+               memcpy(&wq, rlptr, sizeof(void *));
+
+               /*
+                * The waitq is part of the selinfo structure managed by the
+                * driver. For certain drivers, we want to hook the knote into
+                * the selinfo structure's si_note field so selwakeup can call
+                * KNOTE.
+                */
+               si = selinfo_from_waitq(wq);
+
+               /*
+                * The waitq_get_prepost_id() function will (potentially)
+                * allocate a prepost table object for the waitq and return
+                * the table object's ID to us.  It will also set the
+                * waitq_prepost_id field within the waitq structure.
+                *
+                * We can just overwrite kn_hook_waitqid because it's simply a
+                * table ID used to grab a reference when needed.
+                *
+                * We have a reference on the vnode, so we know that the
+                * device won't go away while we get this ID.
+                *
+                * Note: on 32bit this field is 32bit only.
+                */
+               kn->kn_hook_waitqid = (typeof(kn->kn_hook_waitqid))waitq_get_prepost_id(wq);
+       } else if (selres == 0) {
+               /*
+                * The device indicated that there's no data to read, but didn't call
+                * `selrecord`.  Nothing will be notified of changes to this vnode, so
+                * return an error back to user space, to make it clear that the knote
+                * is not attached.
+                */
+               knote_set_error(kn, ENODEV);
+       }
+
+       vnode_put(vp);
+
+       return selres;
+}
+
+static int
+filt_spec_common(struct knote *kn, struct kevent_qos_s *kev, int selres)
+{
+       int64_t data;
+       int ret;
+
+       if (kn->kn_vnode_use_ofst) {
+               if (kn->kn_fp->f_fglob->fg_offset >= (uint32_t)selres) {
+                       data = 0;
+               } else {
+                       data = ((uint32_t)selres) - kn->kn_fp->f_fglob->fg_offset;
+               }
+       } else {
+               data = selres;
+       }
+
+       ret = data >= knote_low_watermark(kn);
+
+       if (ret && kev) {
+               knote_fill_kevent(kn, kev, data);
+       }
+
+       return ret;
 }
 
-static int 
-filt_specattach(struct knote *kn)
+static int
+filt_specattach(struct knote *kn, __unused struct kevent_qos_s *kev)
 {
        vnode_t vp;
        dev_t dev;
@@ -1618,131 +3046,117 @@ filt_specattach(struct knote *kn)
 
        dev = vnode_specrdev(vp);
 
-       if (major(dev) > nchrdev) {
-               return ENXIO;
+       /*
+        * For a few special kinds of devices, we can attach knotes with
+        * no restrictions because their "select" vectors return the amount
+        * of data available.  Others require an explicit NOTE_LOWAT with
+        * data of 1, indicating that the caller doesn't care about actual
+        * data counts, just an indication that the device has data.
+        */
+       if (!kn->kn_vnode_kqok &&
+           ((kn->kn_sfflags & NOTE_LOWAT) == 0 || kn->kn_sdata != 1)) {
+               knote_set_error(kn, EINVAL);
+               return 0;
        }
 
-       if ((cdevsw_flags[major(dev)] & CDEVSW_SELECT_KQUEUE) == 0) {
-               return EINVAL;
+       /*
+        * This forces the select fallback to call through VNOP_SELECT and hook
+        * up selinfo on every filter routine.
+        *
+        * Pseudo-terminal controllers are opted out of native kevent support --
+        * remove this when they get their own EVFILTID.
+        */
+       if (cdevsw_flags[major(dev)] & CDEVSW_IS_PTC) {
+               kn->kn_vnode_kqok = 0;
        }
 
-       /* Resulting wql is safe to unlink even if it has never been linked */
-       kn->kn_hook = wait_queue_link_allocate();
-       if (kn->kn_hook == NULL) {
-               return EAGAIN;
-       }
+       kn->kn_filtid = EVFILTID_SPEC;
+       kn->kn_hook_waitqid = 0;
+
+       knote_markstayactive(kn);
+       return spec_knote_select_and_link(kn);
+}
 
-       kn->kn_fop = &spec_filtops;
-       kn->kn_hookid = vnode_vid(vp);
+static void
+filt_specdetach(struct knote *kn)
+{
+       knote_clearstayactive(kn);
 
-       knote_markstayqueued(kn);
+       /*
+        * This is potentially tricky: the device's selinfo waitq that was
+        * tricked into being part of this knote's waitq set may not be a part
+        * of any other set, and the device itself may have revoked the memory
+        * in which the waitq was held. We use the knote's kn_hook_waitqid field
+        * to keep the ID of the waitq's prepost table object. This
+        * object keeps a pointer back to the waitq, and gives us a safe way
+        * to decouple the dereferencing of driver allocated memory: if the
+        * driver goes away (taking the waitq with it) then the prepost table
+        * object will be invalidated. The waitq details are handled in the
+        * waitq API invoked here.
+        */
+       if (kn->kn_hook_waitqid) {
+               waitq_unlink_by_prepost_id(kn->kn_hook_waitqid, &(knote_get_kq(kn)->kq_wqs));
+               kn->kn_hook_waitqid = 0;
+       }
+}
 
+static int
+filt_specevent(struct knote *kn, __unused long hint)
+{
+       /*
+        * Nothing should call knote or knote_vanish on this knote.
+        */
+       panic("filt_specevent(%p)", kn);
        return 0;
 }
 
-static void 
-filt_specdetach(struct knote *kn)
+static int
+filt_spectouch(struct knote *kn, struct kevent_qos_s *kev)
 {
-       kern_return_t ret;
+       kn->kn_sdata = kev->data;
+       kn->kn_sfflags = kev->fflags;
 
-       /* 
-        * Given wait queue link and wait queue set, unlink.  This is subtle.
-        * If the device has been revoked from under us, selclearthread() will
-        * have removed our link from the kqueue's wait queue set, which 
-        * wait_queue_set_unlink_one() will detect and handle.
-        */
-       ret = wait_queue_set_unlink_one(kn->kn_kq->kq_wqs, kn->kn_hook);
-       if (ret != KERN_SUCCESS) {
-               panic("filt_specdetach(): failed to unlink wait queue link.");
+       if (kev->flags & EV_ENABLE) {
+               return spec_knote_select_and_link(kn);
        }
 
-       (void)wait_queue_link_free(kn->kn_hook);
-       kn->kn_hook = NULL;
-       kn->kn_status &= ~KN_STAYQUEUED;
+       return 0;
 }
 
-static int 
-filt_spec(struct knote *kn, long hint)
+static int
+filt_specprocess(struct knote *kn, struct kevent_qos_s *kev)
 {
        vnode_t vp;
        uthread_t uth;
-       wait_queue_set_t old_wqs;
        vfs_context_t ctx;
+       int res;
        int selres;
        int error;
-       int use_offset;
-       dev_t dev;
-       uint64_t flags;
-
-       assert(kn->kn_hook != NULL);
-
-       if (hint != 0) {
-               panic("filt_spec(): nonzero hint?");
-       }
 
        uth = get_bsdthread_info(current_thread());
        ctx = vfs_context_current();
        vp = (vnode_t)kn->kn_fp->f_fglob->fg_data;
 
-       error = vnode_getwithvid(vp, kn->kn_hookid);
+       error = vnode_getwithvid(vp, vnode_vid(vp));
        if (error != 0) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
+               knote_fill_kevent(kn, kev, 0);
                return 1;
        }
-       
-       dev = vnode_specrdev(vp);
-       flags = cdevsw_flags[major(dev)];
-       use_offset = ((flags & CDEVSW_USE_OFFSET) != 0);
-       assert((flags & CDEVSW_SELECT_KQUEUE) != 0);
-
-       /* Trick selrecord() into hooking kqueue's wait queue set into device wait queue */
-       old_wqs = uth->uu_wqset;
-       uth->uu_wqset = kn->kn_kq->kq_wqs;
-       selres = VNOP_SELECT(vp, filter_to_seltype(kn->kn_filter), 0, kn->kn_hook, ctx);
-       uth->uu_wqset = old_wqs;
 
-       if (use_offset) {
-               if (kn->kn_fp->f_fglob->fg_offset >= (uint32_t)selres) {
-                       kn->kn_data = 0;
-               } else {
-                       kn->kn_data = ((uint32_t)selres) - kn->kn_fp->f_fglob->fg_offset;
-               }
-       } else {
-               kn->kn_data = selres;
-       }
+       selres = spec_knote_select_and_link(kn);
+       res = filt_spec_common(kn, kev, selres);
 
        vnode_put(vp);
 
-       return (kn->kn_data != 0);
+       return res;
 }
 
-static unsigned
+static int
 filt_specpeek(struct knote *kn)
 {
-       vnode_t vp;
-       uthread_t uth;
-       wait_queue_set_t old_wqs;
-       vfs_context_t ctx;
-       int error, selres;
-       
-       uth = get_bsdthread_info(current_thread());
-       ctx = vfs_context_current();
-       vp = (vnode_t)kn->kn_fp->f_fglob->fg_data;
-
-       error = vnode_getwithvid(vp, kn->kn_hookid);
-       if (error != 0) {
-               return 1; /* Just like VNOP_SELECT() on recycled vnode */
-       }
+       int selres = 0;
 
-       /*
-        * Why pass the link here?  Because we may not have registered in the past...
-        */
-       old_wqs = uth->uu_wqset;
-       uth->uu_wqset = kn->kn_kq->kq_wqs;
-       selres = VNOP_SELECT(vp, filter_to_seltype(kn->kn_filter), 0, kn->kn_hook, ctx);
-       uth->uu_wqset = old_wqs;
-
-       vnode_put(vp);
-       return selres;
+       selres = spec_knote_select_and_link(kn);
+       return filt_spec_common(kn, NULL, selres);
 }
-