xnu-4570.71.2.tar.gz

[apple/xnu.git] / bsd / vm / vnode_pager.c

/*
 * Copyright (c) 2000-2006 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
 * 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_OSREFERENCE_LICENSE_HEADER_END@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1987 Carnegie-Mellon University
 * All rights reserved.  The CMU software License Agreement specifies
 * the terms and conditions for use and redistribution.
 */
/*
 *      File:   vnode_pager.c
 *
 *      "Swap" pager that pages to/from vnodes.  Also
 *      handles demand paging from files.
 *
 */

#include <mach/boolean.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/user.h>
#include <sys/proc.h>
#include <sys/kauth.h>
#include <sys/buf.h>
#include <sys/uio.h>
#include <sys/vnode_internal.h>
#include <sys/namei.h>
#include <sys/mount_internal.h> /* needs internal due to fhandle_t */
#include <sys/ubc_internal.h>
#include <sys/lock.h>
#include <sys/disk.h>           /* For DKIOC calls */

#include <mach/mach_types.h>
#include <mach/memory_object_types.h>
#include <mach/memory_object_control.h>
#include <mach/vm_map.h>
#include <mach/mach_vm.h>
#include <mach/upl.h>
#include <mach/sdt.h>

#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <kern/zalloc.h>
#include <kern/kalloc.h>
#include <libkern/libkern.h>

#include <vm/vnode_pager.h>
#include <vm/vm_pageout.h>

#include <kern/assert.h>
#include <sys/kdebug.h>
#include <nfs/rpcv2.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>

#include <vm/vm_protos.h>

#include <vfs/vfs_disk_conditioner.h>

void
vnode_pager_throttle()
{
        struct uthread *ut;

        ut = get_bsdthread_info(current_thread());

        if (ut->uu_lowpri_window)
                throttle_lowpri_io(1);
}

boolean_t
vnode_pager_isSSD(vnode_t vp)
{
        return disk_conditioner_mount_is_ssd(vp->v_mount);
}

#if CONFIG_IOSCHED
void
vnode_pager_issue_reprioritize_io(struct vnode *devvp, uint64_t blkno, uint32_t len, int priority)
{
        u_int32_t blocksize = 0;
        dk_extent_t extent;
        dk_set_tier_t set_tier;
        int error = 0;

        error = VNOP_IOCTL(devvp, DKIOCGETBLOCKSIZE, (caddr_t)&blocksize, 0, vfs_context_kernel());
        if (error)
                return;

        memset(&extent, 0, sizeof(dk_extent_t));
        memset(&set_tier, 0, sizeof(dk_set_tier_t));
        
        extent.offset = blkno * (u_int64_t) blocksize;
        extent.length = len;

        set_tier.extents = &extent; 
        set_tier.extentsCount = 1;
        set_tier.tier = priority;
                
        error = VNOP_IOCTL(devvp, DKIOCSETTIER, (caddr_t)&set_tier, 0, vfs_context_kernel());
        return;
}
#endif

uint32_t
vnode_pager_isinuse(struct vnode *vp)
{
        if (vp->v_usecount > vp->v_kusecount)
                return (1);
        return (0);
}

uint32_t
vnode_pager_return_throttle_io_limit(struct vnode *vp, uint32_t *limit)
{
        return(cluster_throttle_io_limit(vp, limit));
}

vm_object_offset_t
vnode_pager_get_filesize(struct vnode *vp)
{
        return (vm_object_offset_t) ubc_getsize(vp);
}

extern int safe_getpath(struct vnode *dvp, char *leafname, char *path, int _len, int *truncated_path);

kern_return_t
vnode_pager_get_name(
        struct vnode    *vp,
        char            *pathname,
        vm_size_t       pathname_len,
        char            *filename,
        vm_size_t       filename_len,
        boolean_t       *truncated_path_p)
{
        *truncated_path_p = FALSE;
        if (pathname != NULL) {
                /* get the path name */
                safe_getpath(vp, NULL,
                             pathname, (int) pathname_len,
                             truncated_path_p);
        }
        if ((pathname == NULL || *truncated_path_p) &&
            filename != NULL) {
                /* get the file name */
                const char *name;

                name = vnode_getname_printable(vp);
                strlcpy(filename, name, (size_t) filename_len);
                vnode_putname_printable(name);
        }
        return KERN_SUCCESS;
}

kern_return_t
vnode_pager_get_mtime(
        struct vnode    *vp,
        struct timespec *current_mtime,
        struct timespec *cs_mtime)
{
        vnode_mtime(vp, current_mtime, vfs_context_current());
        if (cs_mtime != NULL) {
                ubc_get_cs_mtime(vp, cs_mtime);
        }
        return KERN_SUCCESS;
}

kern_return_t
vnode_pager_get_cs_blobs(
        struct vnode    *vp,
        void            **blobs)
{
        *blobs = ubc_get_cs_blobs(vp);
        return KERN_SUCCESS;
}

/* 
 * vnode_trim:
 * Used to call the DKIOCUNMAP ioctl on the underlying disk device for the specified vnode.
 * Trims the region at offset bytes into the file, for length bytes.
 *
 * Care must be taken to ensure that the vnode is sufficiently reference counted at the time this
 * function is called; no iocounts or usecounts are taken on the vnode.
 * This function is non-idempotent in error cases;  We cannot un-discard the blocks if only some of them
 * are successfully discarded.
 */
u_int32_t vnode_trim (
                struct vnode *vp,
                off_t offset,
                size_t length)
{
        daddr64_t io_blockno;    /* Block number corresponding to the start of the extent */
        size_t io_bytecount;    /* Number of bytes in current extent for the specified range */
        size_t trimmed = 0;
        off_t current_offset = offset; 
        size_t remaining_length = length;
        int error = 0;
        u_int32_t blocksize = 0;
        struct vnode *devvp;
        dk_extent_t extent;
        dk_unmap_t unmap;


        /* Get the underlying device vnode */
        devvp = vp->v_mount->mnt_devvp;

        /* Figure out the underlying device block size */
        error  = VNOP_IOCTL(devvp, DKIOCGETBLOCKSIZE, (caddr_t)&blocksize, 0, vfs_context_kernel());
        if (error) {
                goto trim_exit;
        }

        /* 
         * We may not get the entire range from offset -> offset+length in a single
         * extent from the blockmap call.  Keep looping/going until we are sure we've hit
         * the whole range or if we encounter an error.
         */
        while (trimmed < length) {
                /*
                 * VNOP_BLOCKMAP will tell us the logical to physical block number mapping for the
                 * specified offset.  It returns blocks in contiguous chunks, so if the logical range is 
                 * broken into multiple extents, it must be called multiple times, increasing the offset
                 * in each call to ensure that the entire range is covered.
                 */
                error = VNOP_BLOCKMAP (vp, current_offset, remaining_length, 
                                &io_blockno, &io_bytecount, NULL, VNODE_READ | VNODE_BLOCKMAP_NO_TRACK, NULL);

                if (error) {
                        goto trim_exit;
                }
                /* 
                 * We have a contiguous run.  Prepare & issue the ioctl for the device.
                 * the DKIOCUNMAP ioctl takes offset in bytes from the start of the device.
                 */
                memset (&extent, 0, sizeof(dk_extent_t));
                memset (&unmap, 0, sizeof(dk_unmap_t));
                extent.offset = (uint64_t) io_blockno * (u_int64_t) blocksize;
                extent.length = io_bytecount;
                unmap.extents = &extent;
                unmap.extentsCount = 1;
                error = VNOP_IOCTL(devvp, DKIOCUNMAP, (caddr_t)&unmap, 0, vfs_context_kernel());

                if (error) {
                        goto trim_exit;
                }
                remaining_length = remaining_length - io_bytecount;
                trimmed = trimmed + io_bytecount;
                current_offset = current_offset + io_bytecount;
        }
trim_exit:

        return error;

}

pager_return_t
vnode_pageout(struct vnode *vp,
        upl_t                   upl,
        upl_offset_t            upl_offset,
        vm_object_offset_t      f_offset,
        upl_size_t              size,
        int                     flags,
        int                     *errorp)
{
        int             result = PAGER_SUCCESS;
        int             error = 0;
        int             error_ret = 0;
        daddr64_t blkno;
        int isize;
        int pg_index;
        int base_index;
        upl_offset_t offset;
        upl_page_info_t *pl;
        vfs_context_t ctx = vfs_context_current();      /* pager context */

        isize = (int)size;

        if (isize <= 0) {
                result    = PAGER_ERROR;
                error_ret = EINVAL;
                goto out;
        }

        if (UBCINFOEXISTS(vp) == 0) {
                result    = PAGER_ERROR;
                error_ret = EINVAL;

                if (upl && !(flags & UPL_NOCOMMIT))
                        ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY);
                goto out;
        }
        if ( !(flags & UPL_VNODE_PAGER)) {
                /*
                 * This is a pageout from the default pager,
                 * just go ahead and call vnop_pageout since
                 * it has already sorted out the dirty ranges
                 */
                KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                        (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_START, 
                        size, 1, 0, 0, 0);

                if ( (error_ret = VNOP_PAGEOUT(vp, upl, upl_offset, (off_t)f_offset,
                                               (size_t)size, flags, ctx)) )
                        result = PAGER_ERROR;

                KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                        (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_END, 
                        size, 1, 0, 0, 0);

                goto out;
        }
        if (upl == NULL) {
                int                     request_flags;

                if (vp->v_mount->mnt_vtable->vfc_vfsflags & VFC_VFSVNOP_PAGEOUTV2) {
                        /*
                         * filesystem has requested the new form of VNOP_PAGEOUT for file
                         * backed objects... we will not grab the UPL befofe calling VNOP_PAGEOUT...
                         * it is the fileystem's responsibility to grab the range we're denoting
                         * via 'f_offset' and 'size' into a UPL... this allows the filesystem to first
                         * take any locks it needs, before effectively locking the pages into a UPL...
                         */
                        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, 
                                (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_START, 
                                size, (int)f_offset, 0, 0, 0);

                        if ( (error_ret = VNOP_PAGEOUT(vp, NULL, upl_offset, (off_t)f_offset,
                                                       size, flags, ctx)) ) {
                                result = PAGER_ERROR;
                        }
                        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                                (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_END, 
                                size, 0, 0, 0, 0);

                        goto out;
                }
                if (flags & UPL_MSYNC)
                        request_flags = UPL_UBC_MSYNC | UPL_RET_ONLY_DIRTY;
                else
                        request_flags = UPL_UBC_PAGEOUT | UPL_RET_ONLY_DIRTY;
                
                if (ubc_create_upl_kernel(vp, f_offset, size, &upl, &pl, request_flags, VM_KERN_MEMORY_FILE) != KERN_SUCCESS) {
                        result    = PAGER_ERROR;
                        error_ret = EINVAL;
                        goto out;
                }
                upl_offset = 0;
        } else 
                pl = ubc_upl_pageinfo(upl);

        /*
         * Ignore any non-present pages at the end of the
         * UPL so that we aren't looking at a upl that 
         * may already have been freed by the preceeding
         * aborts/completions.
         */
        base_index = upl_offset / PAGE_SIZE;

        for (pg_index = (upl_offset + isize) / PAGE_SIZE; pg_index > base_index;) {
                if (upl_page_present(pl, --pg_index))
                        break;
                if (pg_index == base_index) {
                        /*
                         * no pages were returned, so release
                         * our hold on the upl and leave
                         */
                        if ( !(flags & UPL_NOCOMMIT))
                                ubc_upl_abort_range(upl, upl_offset, isize, UPL_ABORT_FREE_ON_EMPTY);

                        goto out;
                }
        }
        isize = ((pg_index + 1) - base_index) * PAGE_SIZE;

        /*
         * we come here for pageouts to 'real' files and
         * for msyncs...  the upl may not contain any
         * dirty pages.. it's our responsibility to sort
         * through it and find the 'runs' of dirty pages
         * to call VNOP_PAGEOUT on...
         */

        if (ubc_getsize(vp) == 0) {
                /*
                 * if the file has been effectively deleted, then
                 * we need to go through the UPL and invalidate any
                 * buffer headers we might have that reference any
                 * of it's pages
                 */
                for (offset = upl_offset; isize; isize -= PAGE_SIZE, offset += PAGE_SIZE) {
#if NFSCLIENT
                        if (vp->v_tag == VT_NFS)
                                /* check with nfs if page is OK to drop */
                                error = nfs_buf_page_inval(vp, (off_t)f_offset);
                        else
#endif
                        {
                                blkno = ubc_offtoblk(vp, (off_t)f_offset);
                                error = buf_invalblkno(vp, blkno, 0);
                        }
                        if (error) {
                                if ( !(flags & UPL_NOCOMMIT))
                                        ubc_upl_abort_range(upl, offset, PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY);
                                if (error_ret == 0)
                                        error_ret = error;
                                result = PAGER_ERROR;

                        } else if ( !(flags & UPL_NOCOMMIT)) {
                                ubc_upl_commit_range(upl, offset, PAGE_SIZE, UPL_COMMIT_FREE_ON_EMPTY);
                        }
                        f_offset += PAGE_SIZE;
                }
                goto out;
        }

        offset = upl_offset;
        pg_index = base_index;

        while (isize) {
                int  xsize;
                int  num_of_pages;

                if ( !upl_page_present(pl, pg_index)) {
                        /*
                         * we asked for RET_ONLY_DIRTY, so it's possible
                         * to get back empty slots in the UPL
                         * just skip over them
                         */
                        f_offset += PAGE_SIZE;
                        offset   += PAGE_SIZE;
                        isize    -= PAGE_SIZE;
                        pg_index++;

                        continue;
                }
                if ( !upl_dirty_page(pl, pg_index)) {
                        /*
                         * if the page is not dirty and reached here it is
                         * marked precious or it is due to invalidation in
                         * memory_object_lock request as part of truncation
                         * We also get here from vm_object_terminate()
                         * So all you need to do in these
                         * cases is to invalidate incore buffer if it is there
                         * Note we must not sleep here if the buffer is busy - that is
                         * a lock inversion which causes deadlock.
                         */
#if NFSCLIENT
                        if (vp->v_tag == VT_NFS)
                                /* check with nfs if page is OK to drop */
                                error = nfs_buf_page_inval(vp, (off_t)f_offset);
                        else
#endif
                        {
                                blkno = ubc_offtoblk(vp, (off_t)f_offset);
                                error = buf_invalblkno(vp, blkno, 0);
                        }
                        if (error) {
                                if ( !(flags & UPL_NOCOMMIT))
                                        ubc_upl_abort_range(upl, offset, PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY);
                                if (error_ret == 0)
                                        error_ret = error;
                                result = PAGER_ERROR;

                        } else if ( !(flags & UPL_NOCOMMIT)) {
                                ubc_upl_commit_range(upl, offset, PAGE_SIZE, UPL_COMMIT_FREE_ON_EMPTY);
                        }
                        f_offset += PAGE_SIZE;
                        offset   += PAGE_SIZE;
                        isize    -= PAGE_SIZE;
                        pg_index++;

                        continue;
                }
                num_of_pages = 1;
                xsize = isize - PAGE_SIZE;

                while (xsize) {
                        if ( !upl_dirty_page(pl, pg_index + num_of_pages))
                                break;
                        num_of_pages++;
                        xsize -= PAGE_SIZE;
                }
                xsize = num_of_pages * PAGE_SIZE;

                KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                        (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_START, 
                        xsize, (int)f_offset, 0, 0, 0);

                if ( (error = VNOP_PAGEOUT(vp, upl, offset, (off_t)f_offset,
                                           xsize, flags, ctx)) ) {
                        if (error_ret == 0)
                                error_ret = error;
                        result = PAGER_ERROR;
                }
                KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                        (MACHDBG_CODE(DBG_MACH_VM, 1)) | DBG_FUNC_END, 
                        xsize, 0, 0, 0, 0);

                f_offset += xsize;
                offset   += xsize;
                isize    -= xsize;
                pg_index += num_of_pages;
        }
out:
        if (errorp)
                *errorp = error_ret;

        return (result);
}


pager_return_t
vnode_pagein(
        struct vnode            *vp,
        upl_t                   upl,
        upl_offset_t            upl_offset,
        vm_object_offset_t      f_offset,
        upl_size_t              size,
        int                     flags,
        int                     *errorp)
{
        upl_page_info_t *pl;
        int             result = PAGER_SUCCESS;
        int             error = 0;
        int             pages_in_upl;
        int             start_pg;
        int             last_pg;
        int             first_pg;
        int             xsize;
        int             must_commit = 1;
        int             ignore_valid_page_check = 0;

        if (flags & UPL_NOCOMMIT)
                must_commit = 0;

        if (flags & UPL_IGNORE_VALID_PAGE_CHECK)
                ignore_valid_page_check = 1;

        if (UBCINFOEXISTS(vp) == 0) {
                result = PAGER_ERROR;
                error  = PAGER_ERROR;

                if (upl && must_commit)
                        ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR);

                goto out;
        }
        if (upl == (upl_t)NULL) {
                flags &= ~UPL_NOCOMMIT;

                if (size > MAX_UPL_SIZE_BYTES) {
                        result = PAGER_ERROR;
                        error  = PAGER_ERROR;
                        goto out;
                }
                if (vp->v_mount->mnt_vtable->vfc_vfsflags & VFC_VFSVNOP_PAGEINV2) {
                        /*
                         * filesystem has requested the new form of VNOP_PAGEIN for file
                         * backed objects... we will not grab the UPL befofe calling VNOP_PAGEIN...
                         * it is the fileystem's responsibility to grab the range we're denoting
                         * via 'f_offset' and 'size' into a UPL... this allows the filesystem to first
                         * take any locks it needs, before effectively locking the pages into a UPL...
                         * so we pass a NULL into the filesystem instead of a UPL pointer... the 'upl_offset'
                         * is used to identify the "must have" page in the extent... the filesystem is free
                         * to clip the extent to better fit the underlying FS blocksize if it desires as 
                         * long as it continues to include the "must have" page... 'f_offset' + 'upl_offset'
                         * identifies that page
                         */
                        if ( (error = VNOP_PAGEIN(vp, NULL, upl_offset, (off_t)f_offset,
                                                  size, flags, vfs_context_current())) ) {
                                result = PAGER_ERROR;
                                error  = PAGER_ERROR;
                        }
                        goto out;
                }
                ubc_create_upl_kernel(vp, f_offset, size, &upl, &pl, UPL_UBC_PAGEIN | UPL_RET_ONLY_ABSENT, VM_KERN_MEMORY_FILE);

                if (upl == (upl_t)NULL) {
                        result =  PAGER_ABSENT;
                        error = PAGER_ABSENT;
                        goto out;
                }
                ubc_upl_range_needed(upl, upl_offset / PAGE_SIZE, 1);

                upl_offset = 0;
                first_pg = 0;
                
                /*
                 * if we get here, we've created the upl and
                 * are responsible for commiting/aborting it
                 * regardless of what the caller has passed in
                 */
                must_commit = 1;
        } else {
                pl = ubc_upl_pageinfo(upl);
                first_pg = upl_offset / PAGE_SIZE;
        }
        pages_in_upl = size / PAGE_SIZE;
        DTRACE_VM2(pgpgin, int, pages_in_upl, (uint64_t *), NULL);

        /*
         * before we start marching forward, we must make sure we end on 
         * a present page, otherwise we will be working with a freed
         * upl
         */
        for (last_pg = pages_in_upl - 1; last_pg >= first_pg; last_pg--) {
                if (upl_page_present(pl, last_pg))
                        break;
                if (last_pg == first_pg) {
                        /*
                         * empty UPL, no pages are present
                         */
                        if (must_commit)
                                ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY);
                        goto out;
                }
        }
        pages_in_upl = last_pg + 1;
        last_pg = first_pg;

        while (last_pg < pages_in_upl) {
                /*
                 * skip over missing pages...
                 */
                for ( ; last_pg < pages_in_upl; last_pg++) {
                        if (upl_page_present(pl, last_pg))
                                break;
                }

                if (ignore_valid_page_check == 1) {
                        start_pg = last_pg;
                } else {
                        /*
                         * skip over 'valid' pages... we don't want to issue I/O for these
                         */
                        for (start_pg = last_pg; last_pg < pages_in_upl; last_pg++) {
                                if (!upl_valid_page(pl, last_pg))
                                        break;
                        }
                }

                if (last_pg > start_pg) {
                        /*
                         * we've found a range of valid pages
                         * if we've got COMMIT responsibility
                         * commit this range of pages back to the
                         * cache unchanged
                         */
                        xsize = (last_pg - start_pg) * PAGE_SIZE;

                        if (must_commit)
                                ubc_upl_abort_range(upl, start_pg * PAGE_SIZE, xsize, UPL_ABORT_FREE_ON_EMPTY);
                }
                if (last_pg == pages_in_upl)
                        /*
                         * we're done... all pages that were present
                         * have either had I/O issued on them or 
                         * were aborted unchanged...
                         */
                        break;

                if (!upl_page_present(pl, last_pg)) {
                        /*
                         * we found a range of valid pages 
                         * terminated by a missing page...
                         * bump index to the next page and continue on
                         */
                        last_pg++;
                        continue;
                }
                /*
                 * scan from the found invalid page looking for a valid
                 * or non-present page before the end of the upl is reached, if we
                 * find one, then it will be the last page of the request to
                 * 'cluster_io'
                 */
                for (start_pg = last_pg; last_pg < pages_in_upl; last_pg++) {
                        if (( !ignore_valid_page_check && upl_valid_page(pl, last_pg)) || !upl_page_present(pl, last_pg))
                                break;
                }
                if (last_pg > start_pg) {
                        int xoff;
                        xsize = (last_pg - start_pg) * PAGE_SIZE;
                        xoff  = start_pg * PAGE_SIZE;

                        if ( (error = VNOP_PAGEIN(vp, upl, (upl_offset_t) xoff,
                                               (off_t)f_offset + xoff,
                                               xsize, flags, vfs_context_current())) ) {
                                /*
                                 * Usually this UPL will be aborted/committed by the lower cluster layer.
                                 *
                                 * a)   In the case of decmpfs, however, we may return an error (EAGAIN) to avoid
                                 *      a deadlock with another thread already inflating the file. 
                                 *
                                 * b)   In the case of content protection, EPERM is a valid error and we should respect it.
                                 *
                                 * In those cases, we must take care of our UPL at this layer itself.
                                 */
                                if (must_commit) {
                                        if(error == EAGAIN) {
                                                ubc_upl_abort_range(upl, (upl_offset_t) xoff, xsize, UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_RESTART);
                                        }
                                        if(error == EPERM) {
                                                ubc_upl_abort_range(upl, (upl_offset_t) xoff, xsize, UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR);
                                        }
                                }
                                result = PAGER_ERROR;
                                error  = PAGER_ERROR;

                        }
                }
        }
out:
        if (errorp)
                *errorp = result;

        return (error);
}

void *
upl_get_internal_page_list(upl_t upl)
{
  return(UPL_GET_INTERNAL_PAGE_LIST(upl));

}