xnu-792.12.6.tar.gz

[apple/xnu.git] / bsd / miscfs / specfs / spec_vnops.c

/*
 * Copyright (c) 2006 Apple Computer, Inc. All Rights Reserved.
 * 
 * @APPLE_LICENSE_OSREFERENCE_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 
 * compliance with the License.  The rights granted to you under the 
 * License may not be used to create, or enable the creation or 
 * redistribution of, 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, 
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 
 * 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_LICENSE_OSREFERENCE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1989, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)spec_vnops.c        8.14 (Berkeley) 5/21/95
 */

#include <sys/param.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/conf.h>
#include <sys/buf_internal.h>
#include <sys/mount_internal.h>
#include <sys/namei.h>
#include <sys/vnode_internal.h>
#include <sys/stat.h>
#include <sys/errno.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/user.h>
#include <sys/malloc.h>
#include <sys/disk.h>
#include <sys/uio_internal.h>
#include <miscfs/specfs/specdev.h>
#include <vfs/vfs_support.h>

#include <sys/kdebug.h>

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";

#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_devblocksize_desc, (VOPFUNC)spec_devblocksize }, /* devblocksize */
        { &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 }
};
struct vnodeopv_desc spec_vnodeop_opv_desc =
        { &spec_vnodeop_p, spec_vnodeop_entries };


static void set_blocksize(vnode_t, dev_t);


/*
 * Trivial lookup routine that always fails.
 */
int
spec_lookup(ap)
        struct vnop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                vfs_context_t a_context;
        } */ *ap;
{

        *ap->a_vpp = NULL;
        return (ENOTDIR);
}

static void
set_blocksize(struct vnode *vp, dev_t dev)
{
    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;
}

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)
                        return;

                vnode_lock(vp);
                set_blocksize(vp, dev);
                vnode_unlock(vp);
        }

}


/*
 * Open a special file.
 */
int
spec_open(ap)
        struct vnop_open_args /* {
                struct vnode *a_vp;
                int  a_mode;
                vfs_context_t a_context;
        } */ *ap;
{
        struct proc *p = vfs_context_proc(ap->a_context);
        kauth_cred_t cred = vfs_context_ucred(ap->a_context);
        struct vnode *vp = ap->a_vp;
        dev_t bdev, dev = (dev_t)vp->v_rdev;
        int maj = major(dev);
        int error;

        /*
         * Don't allow open if fs is mounted -nodev.
         */
        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 (cred != FSCRED && (ap->a_mode & FWRITE)) {
                        /*
                         * 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);
                        /*
                         * 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.
                         */
                        if (securelevel >= 1) {
                                if ((bdev = chrtoblk(dev)) != NODEV && check_mountedon(bdev, VBLK, &error))
                                        return (error);
                                if (iskmemdev(dev))
                                        return (EPERM);
                        }
                }
                if (cdevsw[maj].d_type == D_TTY) {
                        vnode_lock(vp);
                        vp->v_flag |= VISTTY;
                        vnode_unlock(vp);
                }
                error = (*cdevsw[maj].d_open)(dev, ap->a_mode, S_IFCHR, p);
                return (error);

        case VBLK:
                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);
                /*
                 * Do not allow opens of block devices that are
                 * currently mounted.
                 */
                if ( (error = vfs_mountedon(vp)) )
                        return (error);
                error = (*bdevsw[maj].d_open)(dev, ap->a_mode, S_IFBLK, p);
                if (!error) {
                    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)) {
                                /* 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)) {
                                                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;
                    }


                        vnode_lock(vp);
                    set_blocksize(vp, dev);

                    /*
                     * 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 */
                        
                        vnode_unlock(vp);

                }
                return(error);
        default:
                panic("spec_open type");
        }
        return (0);
}

/*
 * Vnode op for read
 */
int
spec_read(ap)
        struct vnop_read_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                int  a_ioflag;
                vfs_context_t a_context;
        } */ *ap;
{
        register struct vnode *vp = ap->a_vp;
        register struct uio *uio = ap->a_uio;
        struct buf *bp;
        daddr64_t bn, nextbn;
        long bsize, bscale;
        int devBlockSize=0;
        int n, on;
        int error = 0;
        dev_t dev;

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_READ)
                panic("spec_read mode");
        if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg))
                panic("spec_read proc");
#endif
        if (uio_resid(uio) == 0)
                return (0);

        switch (vp->v_type) {

        case VCHR:
                error = (*cdevsw[major(vp->v_rdev)].d_read)
                        (vp->v_rdev, uio, ap->a_ioflag);
                return (error);

        case VBLK:
                if (uio->uio_offset < 0)
                        return (EINVAL);

                dev = vp->v_rdev;

                devBlockSize = vp->v_specsize;

                if (devBlockSize > PAGE_SIZE) 
                        return (EINVAL);

                bscale = PAGE_SIZE / devBlockSize;
                bsize = bscale * devBlockSize;

                do {
                        on = uio->uio_offset % bsize;

                        bn = (daddr64_t)((uio->uio_offset / devBlockSize) &~ (bscale - 1));
                        
                        if (vp->v_speclastr + bscale == bn) {
                                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);

                        vnode_lock(vp);
                        vp->v_speclastr = bn;
                        vnode_unlock(vp);

                        n = bsize - buf_resid(bp);
                        if ((on > n) || error) {
                                if (!error)
                                        error = EINVAL;
                                buf_brelse(bp);
                                return (error);
                        }
                        // LP64todo - fix this!
                        n = min((unsigned)(n  - on), uio_resid(uio));

                        error = uiomove((char *)buf_dataptr(bp) + on, n, uio);
                        if (n + on == bsize)
                                buf_markaged(bp);
                        buf_brelse(bp);
                } while (error == 0 && uio_resid(uio) > 0 && n != 0);
                return (error);

        default:
                panic("spec_read type");
        }
        /* NOTREACHED */

        return (0);
}

/*
 * Vnode op for write
 */
int
spec_write(ap)
        struct vnop_write_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                int  a_ioflag;
                vfs_context_t a_context;
        } */ *ap;
{
        register struct vnode *vp = ap->a_vp;
        register struct uio *uio = ap->a_uio;
        struct buf *bp;
        daddr64_t bn;
        int bsize, blkmask, bscale;
        register int io_sync;
        register int io_size;
        int devBlockSize=0;
        register int n, on;
        int error = 0;
        dev_t dev;

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_WRITE)
                panic("spec_write mode");
        if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg))
                panic("spec_write proc");
#endif

        switch (vp->v_type) {

        case VCHR:
                error = (*cdevsw[major(vp->v_rdev)].d_write)
                        (vp->v_rdev, uio, ap->a_ioflag);
                return (error);

        case VBLK:
                if (uio_resid(uio) == 0)
                        return (0);
                if (uio->uio_offset < 0)
                        return (EINVAL);

                io_sync = (ap->a_ioflag & IO_SYNC);
                // LP64todo - fix this!
                io_size = uio_resid(uio);

                dev = (vp->v_rdev);

                devBlockSize = vp->v_specsize;
                if (devBlockSize > PAGE_SIZE)
                        return(EINVAL);

                bscale = PAGE_SIZE / devBlockSize;
                blkmask = bscale - 1;
                bsize = bscale * devBlockSize;
                

                do {
                        bn = (daddr64_t)((uio->uio_offset / devBlockSize) &~ blkmask);
                        on = uio->uio_offset % bsize;

                        // LP64todo - fix this!
                        n = min((unsigned)(bsize - on), uio_resid(uio));

                        /*
                         * Use buf_getblk() as an optimization IFF:
                         *
                         * 1)   We are reading exactly a block on a block
                         *      aligned boundary
                         * 2)   We know the size of the device from spec_open
                         * 3)   The read doesn't span the end of the device
                         *
                         * Otherwise, we fall back on buf_bread().
                         */
                        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;
                        }

                        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)
                                error = (int)buf_error(bp);
                        if (error) {
                                buf_brelse(bp);
                                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);
                        }
                        buf_markaged(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);

        default:
                panic("spec_write type");
        }
        /* NOTREACHED */

        return (0);
}

/*
 * Device ioctl operation.
 */
int
spec_ioctl(ap)
        struct vnop_ioctl_args /* {
                struct vnode *a_vp;
                int  a_command;
                caddr_t  a_data;
                int  a_fflag;
                vfs_context_t a_context;
        } */ *ap;
{
        proc_t p = vfs_context_proc(ap->a_context);
        dev_t dev = ap->a_vp->v_rdev;

        switch (ap->a_vp->v_type) {

        case VCHR:
                return ((*cdevsw[major(dev)].d_ioctl)(dev, ap->a_command, ap->a_data,
                    ap->a_fflag, p));

        case VBLK:
                if (ap->a_command == 0 && (int)ap->a_data == B_TAPE) {
                        if (bdevsw[major(dev)].d_type == D_TAPE)
                                return (0);
                        else
                                return (1);
                }
                return ((*bdevsw[major(dev)].d_ioctl)(dev, ap->a_command, ap->a_data,
                   ap->a_fflag, p));

        default:
                panic("spec_ioctl");
                /* NOTREACHED */
        }
        return (0);
}

int
spec_select(ap)
        struct vnop_select_args /* {
                struct vnode *a_vp;
                int  a_which;
                int  a_fflags;
                void * a_wql;
                vfs_context_t a_context;
        } */ *ap;
{
        proc_t p = vfs_context_proc(ap->a_context);
        register dev_t dev;

        switch (ap->a_vp->v_type) {

        default:
                return (1);             /* XXX */

        case VCHR:
                dev = ap->a_vp->v_rdev;
                return (*cdevsw[major(dev)].d_select)(dev, ap->a_which, ap->a_wql, p);
        }
}

/*
 * Synch buffers associated with a block device
 */
int
spec_fsync_internal(vnode_t vp, int waitfor, __unused vfs_context_t context)
{
        if (vp->v_type == VCHR)
                return (0);
        /*
         * Flush all dirty buffers associated with a block device.
         */
        buf_flushdirtyblks(vp, waitfor == MNT_WAIT, 0, (char *)"spec_fsync");

        return (0);
}

int
spec_fsync(ap)
        struct vnop_fsync_args /* {
                struct vnode *a_vp;
                int  a_waitfor;
                vfs_context_t a_context;
        } */ *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;


#define LOWPRI_DELAY_MSECS      200
#define LOWPRI_WINDOW_MSECS     200

int     lowpri_IO_window_msecs = LOWPRI_WINDOW_MSECS;
int     lowpri_IO_delay_msecs  = LOWPRI_DELAY_MSECS;

struct timeval last_normal_IO_timestamp;
struct timeval last_lowpri_IO_timestamp;
struct timeval lowpri_IO_window = { 0, LOWPRI_WINDOW_MSECS * 1000 };

int
spec_strategy(ap)
        struct vnop_strategy_args /* {
                struct buf *a_bp;
        } */ *ap;
{
        buf_t   bp;
        int     bflags;
        dev_t   bdev;
        proc_t  p;
        struct timeval elapsed;

        bp = ap->a_bp;
        bdev = buf_device(bp);
        bflags = buf_flags(bp);

        if (kdebug_enable) {
                int    code = 0;

                if (bflags & B_READ)
                        code |= DKIO_READ;
                if (bflags & B_ASYNC)
                        code |= DKIO_ASYNC;

                if (bflags & B_META)
                        code |= DKIO_META;
                else if (bflags & B_PAGEIO)
                        code |= DKIO_PAGING;

                KERNEL_DEBUG_CONSTANT(FSDBG_CODE(DBG_DKRW, code) | DBG_FUNC_NONE,
                                      (unsigned int)bp, bdev, (int)buf_blkno(bp), buf_count(bp), 0);
        }
        if (((bflags & (B_PAGEIO | B_READ)) == (B_PAGEIO | B_READ)) &&
            (buf_vnode(bp)->v_mount->mnt_kern_flag & MNTK_ROOTDEV))
                hard_throttle_on_root = 1;

        if ( lowpri_IO_delay_msecs && lowpri_IO_window_msecs ) {
                p = current_proc();

                if ( (p == NULL) || !(p->p_lflag & P_LLOW_PRI_IO)) {
                        if (!(p->p_lflag & P_LBACKGROUND_IO))
                                microuptime(&last_normal_IO_timestamp);
                } else {
                        microuptime(&last_lowpri_IO_timestamp);

                        elapsed = last_lowpri_IO_timestamp;
                        timevalsub(&elapsed, &last_normal_IO_timestamp);

                        lowpri_IO_window.tv_sec  = lowpri_IO_window_msecs / 1000;
                        lowpri_IO_window.tv_usec = (lowpri_IO_window_msecs % 1000) * 1000;

                        if (timevalcmp(&elapsed, &lowpri_IO_window, <)) {
                                struct uthread  *ut;

                                /*
                                 * 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
                                 */
                                ut = get_bsdthread_info(current_thread());
                                ut->uu_lowpri_delay = lowpri_IO_delay_msecs;
                        }
                }
        }
        (*bdevsw[major(bdev)].d_strategy)(bp);

        return (0);
}


/*
 * This is a noop, simply returning what one has been given.
 */
int
spec_blockmap(__unused struct vnop_blockmap_args *ap)
{
        return (ENOTSUP);
}


/*
 * Device close routine
 */
int
spec_close(ap)
        struct vnop_close_args /* {
                struct vnode *a_vp;
                int  a_fflag;
                vfs_context_t a_context;
        } */ *ap;
{
        register struct vnode *vp = ap->a_vp;
        dev_t dev = vp->v_rdev;
        int (*devclose)(dev_t, int, int, struct proc *);
        int mode, error;
        struct proc *p = vfs_context_proc(ap->a_context);

        switch (vp->v_type) {

        case VCHR:
                /*
                 * Hack: a tty device that is a controlling terminal
                 * has a reference from the session structure.
                 * We cannot easily tell that a character device is
                 * a controlling terminal, unless it is the closing
                 * process' controlling terminal.  In that case,
                 * if the reference count is 2 (this last descriptor
                 * plus the session), release the reference from the session.
                 */
                if (vcount(vp) == 2 && p &&
                    vp == p->p_session->s_ttyvp) {
                        p->p_session->s_ttyvp = NULL;
                        vnode_rele(vp);
                }
                /*
                 * close on last reference.
                 */
                if (vcount(vp) > 1)
                        return (0);
                devclose = cdevsw[major(dev)].d_close;
                mode = S_IFCHR;
                break;

        case VBLK:
#ifdef DEVFS_IMPLEMENTS_LOCKING
                /*
                 * On last close of a block device (that isn't mounted)
                 * 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);

                error = buf_invalidateblks(vp, BUF_WRITE_DATA, 0, 0);
                if (error)
                        return (error);
                /*
                 * Since every use (buffer, vnode, swap, blockmap)
                 * holds a reference to the vnode, and because we mark
                 * any other vnodes that alias this device, when the
                 * sum of the reference counts on all the aliased
                 * vnodes descends to one, we are on last close.
                 */
                if (vcount(vp) > 1)
                        return (0);
#else /* DEVFS_IMPLEMENTS_LOCKING */
                /*
                 * Since every use (buffer, vnode, swap, blockmap)
                 * holds a reference to the vnode, and because we mark
                 * any other vnodes that alias this device, when the
                 * sum of the reference counts on all the aliased
                 * vnodes descends to one, we are on last close.
                 */
                if (vcount(vp) > 1)
                        return (0);

                /*
                 * On last close of a block device (that isn't mounted)
                 * 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);

                error = buf_invalidateblks(vp, BUF_WRITE_DATA, 0, 0);
                if (error)
                        return (error);
#endif /* DEVFS_IMPLEMENTS_LOCKING */
                devclose = bdevsw[major(dev)].d_close;
                mode = S_IFBLK;
                break;

        default:
                panic("spec_close: not special");
        }

        return ((*devclose)(dev, ap->a_fflag, mode, p));
}

/*
 * Return POSIX pathconf information applicable to special devices.
 */
int
spec_pathconf(ap)
        struct vnop_pathconf_args /* {
                struct vnode *a_vp;
                int a_name;
                int *a_retval;
                vfs_context_t a_context;
        } */ *ap;
{

        switch (ap->a_name) {
        case _PC_LINK_MAX:
                *ap->a_retval = LINK_MAX;
                return (0);
        case _PC_MAX_CANON:
                *ap->a_retval = MAX_CANON;
                return (0);
        case _PC_MAX_INPUT:
                *ap->a_retval = MAX_INPUT;
                return (0);
        case _PC_PIPE_BUF:
                *ap->a_retval = PIPE_BUF;
                return (0);
        case _PC_CHOWN_RESTRICTED:
                *ap->a_retval = 1;
                return (0);
        case _PC_VDISABLE:
                *ap->a_retval = _POSIX_VDISABLE;
                return (0);
        default:
                return (EINVAL);
        }
        /* NOTREACHED */
}

int
spec_devblocksize(ap)
        struct vnop_devblocksize_args /* {
                struct vnode *a_vp;
                int *a_retval;
        } */ *ap;
{
        *ap->a_retval = (ap->a_vp->v_specsize);
        return (0);
}

/*
 * Special device failed operation
 */
int
spec_ebadf(__unused void *dummy)
{

        return (EBADF);
}

/*
 * Special device bad operation
 */
int
spec_badop()
{

        panic("spec_badop called");
        /* NOTREACHED */
}

/* Blktooff derives file offset from logical block number */
int
spec_blktooff(ap)
        struct vnop_blktooff_args /* {
                struct vnode *a_vp;
                daddr64_t a_lblkno;
                off_t *a_offset;    
        } */ *ap;
{
        register struct vnode *vp = ap->a_vp;

        switch (vp->v_type) {
        case VCHR:
                *ap->a_offset = (off_t)-1; /* failure */
                return (ENOTSUP);

        case VBLK:
                printf("spec_blktooff: not implemented for VBLK\n");
                *ap->a_offset = (off_t)-1; /* failure */
                return (ENOTSUP);

        default:
                panic("spec_blktooff type");
        }
        /* NOTREACHED */

        return (0);
}

/* Offtoblk derives logical block number from file offset */
int
spec_offtoblk(ap)
        struct vnop_offtoblk_args /* {
                struct vnode *a_vp;
                off_t a_offset;    
                daddr64_t *a_lblkno;
        } */ *ap;
{
        register struct vnode *vp = ap->a_vp;

        switch (vp->v_type) {
        case VCHR:
                *ap->a_lblkno = (daddr64_t)-1; /* failure */
                return (ENOTSUP);

        case VBLK:
                printf("spec_offtoblk: not implemented for VBLK\n");
                *ap->a_lblkno = (daddr64_t)-1; /* failure */
                return (ENOTSUP);

        default:
                panic("spec_offtoblk type");
        }
        /* NOTREACHED */

        return (0);
}