xfs: improve metadata I/O merging in the elevator

[safe/jmp/linux-2.6] / fs / xfs / linux-2.6 / xfs_buf.c

/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include <linux/stddef.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/vmalloc.h>
#include <linux/bio.h>
#include <linux/sysctl.h>
#include <linux/proc_fs.h>
#include <linux/workqueue.h>
#include <linux/percpu.h>
#include <linux/blkdev.h>
#include <linux/hash.h>
#include <linux/kthread.h>
#include <linux/migrate.h>
#include <linux/backing-dev.h>
#include <linux/freezer.h>

#include "xfs_sb.h"
#include "xfs_inum.h"
#include "xfs_ag.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_trace.h"

static kmem_zone_t *xfs_buf_zone;
STATIC int xfsbufd(void *);
STATIC int xfsbufd_wakeup(int, gfp_t);
STATIC void xfs_buf_delwri_queue(xfs_buf_t *, int);
static struct shrinker xfs_buf_shake = {
        .shrink = xfsbufd_wakeup,
        .seeks = DEFAULT_SEEKS,
};

static struct workqueue_struct *xfslogd_workqueue;
struct workqueue_struct *xfsdatad_workqueue;
struct workqueue_struct *xfsconvertd_workqueue;

#ifdef XFS_BUF_LOCK_TRACKING
# define XB_SET_OWNER(bp)       ((bp)->b_last_holder = current->pid)
# define XB_CLEAR_OWNER(bp)     ((bp)->b_last_holder = -1)
# define XB_GET_OWNER(bp)       ((bp)->b_last_holder)
#else
# define XB_SET_OWNER(bp)       do { } while (0)
# define XB_CLEAR_OWNER(bp)     do { } while (0)
# define XB_GET_OWNER(bp)       do { } while (0)
#endif

#define xb_to_gfp(flags) \
        ((((flags) & XBF_READ_AHEAD) ? __GFP_NORETRY : \
          ((flags) & XBF_DONT_BLOCK) ? GFP_NOFS : GFP_KERNEL) | __GFP_NOWARN)

#define xb_to_km(flags) \
         (((flags) & XBF_DONT_BLOCK) ? KM_NOFS : KM_SLEEP)

#define xfs_buf_allocate(flags) \
        kmem_zone_alloc(xfs_buf_zone, xb_to_km(flags))
#define xfs_buf_deallocate(bp) \
        kmem_zone_free(xfs_buf_zone, (bp));

/*
 *      Page Region interfaces.
 *
 *      For pages in filesystems where the blocksize is smaller than the
 *      pagesize, we use the page->private field (long) to hold a bitmap
 *      of uptodate regions within the page.
 *
 *      Each such region is "bytes per page / bits per long" bytes long.
 *
 *      NBPPR == number-of-bytes-per-page-region
 *      BTOPR == bytes-to-page-region (rounded up)
 *      BTOPRT == bytes-to-page-region-truncated (rounded down)
 */
#if (BITS_PER_LONG == 32)
#define PRSHIFT         (PAGE_CACHE_SHIFT - 5)  /* (32 == 1<<5) */
#elif (BITS_PER_LONG == 64)
#define PRSHIFT         (PAGE_CACHE_SHIFT - 6)  /* (64 == 1<<6) */
#else
#error BITS_PER_LONG must be 32 or 64
#endif
#define NBPPR           (PAGE_CACHE_SIZE/BITS_PER_LONG)
#define BTOPR(b)        (((unsigned int)(b) + (NBPPR - 1)) >> PRSHIFT)
#define BTOPRT(b)       (((unsigned int)(b) >> PRSHIFT))

STATIC unsigned long
page_region_mask(
        size_t          offset,
        size_t          length)
{
        unsigned long   mask;
        int             first, final;

        first = BTOPR(offset);
        final = BTOPRT(offset + length - 1);
        first = min(first, final);

        mask = ~0UL;
        mask <<= BITS_PER_LONG - (final - first);
        mask >>= BITS_PER_LONG - (final);

        ASSERT(offset + length <= PAGE_CACHE_SIZE);
        ASSERT((final - first) < BITS_PER_LONG && (final - first) >= 0);

        return mask;
}

STATIC void
set_page_region(
        struct page     *page,
        size_t          offset,
        size_t          length)
{
        set_page_private(page,
                page_private(page) | page_region_mask(offset, length));
        if (page_private(page) == ~0UL)
                SetPageUptodate(page);
}

STATIC int
test_page_region(
        struct page     *page,
        size_t          offset,
        size_t          length)
{
        unsigned long   mask = page_region_mask(offset, length);

        return (mask && (page_private(page) & mask) == mask);
}

/*
 *      Mapping of multi-page buffers into contiguous virtual space
 */

typedef struct a_list {
        void            *vm_addr;
        struct a_list   *next;
} a_list_t;

static a_list_t         *as_free_head;
static int              as_list_len;
static DEFINE_SPINLOCK(as_lock);

/*
 *      Try to batch vunmaps because they are costly.
 */
STATIC void
free_address(
        void            *addr)
{
        a_list_t        *aentry;

#ifdef CONFIG_XEN
        /*
         * Xen needs to be able to make sure it can get an exclusive
         * RO mapping of pages it wants to turn into a pagetable.  If
         * a newly allocated page is also still being vmap()ed by xfs,
         * it will cause pagetable construction to fail.  This is a
         * quick workaround to always eagerly unmap pages so that Xen
         * is happy.
         */
        vunmap(addr);
        return;
#endif

        aentry = kmalloc(sizeof(a_list_t), GFP_NOWAIT);
        if (likely(aentry)) {
                spin_lock(&as_lock);
                aentry->next = as_free_head;
                aentry->vm_addr = addr;
                as_free_head = aentry;
                as_list_len++;
                spin_unlock(&as_lock);
        } else {
                vunmap(addr);
        }
}

STATIC void
purge_addresses(void)
{
        a_list_t        *aentry, *old;

        if (as_free_head == NULL)
                return;

        spin_lock(&as_lock);
        aentry = as_free_head;
        as_free_head = NULL;
        as_list_len = 0;
        spin_unlock(&as_lock);

        while ((old = aentry) != NULL) {
                vunmap(aentry->vm_addr);
                aentry = aentry->next;
                kfree(old);
        }
}

/*
 *      Internal xfs_buf_t object manipulation
 */

STATIC void
_xfs_buf_initialize(
        xfs_buf_t               *bp,
        xfs_buftarg_t           *target,
        xfs_off_t               range_base,
        size_t                  range_length,
        xfs_buf_flags_t         flags)
{
        /*
         * We don't want certain flags to appear in b_flags.
         */
        flags &= ~(XBF_LOCK|XBF_MAPPED|XBF_DONT_BLOCK|XBF_READ_AHEAD);

        memset(bp, 0, sizeof(xfs_buf_t));
        atomic_set(&bp->b_hold, 1);
        init_completion(&bp->b_iowait);
        INIT_LIST_HEAD(&bp->b_list);
        INIT_LIST_HEAD(&bp->b_hash_list);
        init_MUTEX_LOCKED(&bp->b_sema); /* held, no waiters */
        XB_SET_OWNER(bp);
        bp->b_target = target;
        bp->b_file_offset = range_base;
        /*
         * Set buffer_length and count_desired to the same value initially.
         * I/O routines should use count_desired, which will be the same in
         * most cases but may be reset (e.g. XFS recovery).
         */
        bp->b_buffer_length = bp->b_count_desired = range_length;
        bp->b_flags = flags;
        bp->b_bn = XFS_BUF_DADDR_NULL;
        atomic_set(&bp->b_pin_count, 0);
        init_waitqueue_head(&bp->b_waiters);

        XFS_STATS_INC(xb_create);

        trace_xfs_buf_init(bp, _RET_IP_);
}

/*
 *      Allocate a page array capable of holding a specified number
 *      of pages, and point the page buf at it.
 */
STATIC int
_xfs_buf_get_pages(
        xfs_buf_t               *bp,
        int                     page_count,
        xfs_buf_flags_t         flags)
{
        /* Make sure that we have a page list */
        if (bp->b_pages == NULL) {
                bp->b_offset = xfs_buf_poff(bp->b_file_offset);
                bp->b_page_count = page_count;
                if (page_count <= XB_PAGES) {
                        bp->b_pages = bp->b_page_array;
                } else {
                        bp->b_pages = kmem_alloc(sizeof(struct page *) *
                                        page_count, xb_to_km(flags));
                        if (bp->b_pages == NULL)
                                return -ENOMEM;
                }
                memset(bp->b_pages, 0, sizeof(struct page *) * page_count);
        }
        return 0;
}

/*
 *      Frees b_pages if it was allocated.
 */
STATIC void
_xfs_buf_free_pages(
        xfs_buf_t       *bp)
{
        if (bp->b_pages != bp->b_page_array) {
                kmem_free(bp->b_pages);
        }
}

/*
 *      Releases the specified buffer.
 *
 *      The modification state of any associated pages is left unchanged.
 *      The buffer most not be on any hash - use xfs_buf_rele instead for
 *      hashed and refcounted buffers
 */
void
xfs_buf_free(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_free(bp, _RET_IP_);

        ASSERT(list_empty(&bp->b_hash_list));

        if (bp->b_flags & (_XBF_PAGE_CACHE|_XBF_PAGES)) {
                uint            i;

                if ((bp->b_flags & XBF_MAPPED) && (bp->b_page_count > 1))
                        free_address(bp->b_addr - bp->b_offset);

                for (i = 0; i < bp->b_page_count; i++) {
                        struct page     *page = bp->b_pages[i];

                        if (bp->b_flags & _XBF_PAGE_CACHE)
                                ASSERT(!PagePrivate(page));
                        page_cache_release(page);
                }
                _xfs_buf_free_pages(bp);
        }

        xfs_buf_deallocate(bp);
}

/*
 *      Finds all pages for buffer in question and builds it's page list.
 */
STATIC int
_xfs_buf_lookup_pages(
        xfs_buf_t               *bp,
        uint                    flags)
{
        struct address_space    *mapping = bp->b_target->bt_mapping;
        size_t                  blocksize = bp->b_target->bt_bsize;
        size_t                  size = bp->b_count_desired;
        size_t                  nbytes, offset;
        gfp_t                   gfp_mask = xb_to_gfp(flags);
        unsigned short          page_count, i;
        pgoff_t                 first;
        xfs_off_t               end;
        int                     error;

        end = bp->b_file_offset + bp->b_buffer_length;
        page_count = xfs_buf_btoc(end) - xfs_buf_btoct(bp->b_file_offset);

        error = _xfs_buf_get_pages(bp, page_count, flags);
        if (unlikely(error))
                return error;
        bp->b_flags |= _XBF_PAGE_CACHE;

        offset = bp->b_offset;
        first = bp->b_file_offset >> PAGE_CACHE_SHIFT;

        for (i = 0; i < bp->b_page_count; i++) {
                struct page     *page;
                uint            retries = 0;

              retry:
                page = find_or_create_page(mapping, first + i, gfp_mask);
                if (unlikely(page == NULL)) {
                        if (flags & XBF_READ_AHEAD) {
                                bp->b_page_count = i;
                                for (i = 0; i < bp->b_page_count; i++)
                                        unlock_page(bp->b_pages[i]);
                                return -ENOMEM;
                        }

                        /*
                         * This could deadlock.
                         *
                         * But until all the XFS lowlevel code is revamped to
                         * handle buffer allocation failures we can't do much.
                         */
                        if (!(++retries % 100))
                                printk(KERN_ERR
                                        "XFS: possible memory allocation "
                                        "deadlock in %s (mode:0x%x)\n",
                                        __func__, gfp_mask);

                        XFS_STATS_INC(xb_page_retries);
                        xfsbufd_wakeup(0, gfp_mask);
                        congestion_wait(BLK_RW_ASYNC, HZ/50);
                        goto retry;
                }

                XFS_STATS_INC(xb_page_found);

                nbytes = min_t(size_t, size, PAGE_CACHE_SIZE - offset);
                size -= nbytes;

                ASSERT(!PagePrivate(page));
                if (!PageUptodate(page)) {
                        page_count--;
                        if (blocksize >= PAGE_CACHE_SIZE) {
                                if (flags & XBF_READ)
                                        bp->b_flags |= _XBF_PAGE_LOCKED;
                        } else if (!PagePrivate(page)) {
                                if (test_page_region(page, offset, nbytes))
                                        page_count++;
                        }
                }

                bp->b_pages[i] = page;
                offset = 0;
        }

        if (!(bp->b_flags & _XBF_PAGE_LOCKED)) {
                for (i = 0; i < bp->b_page_count; i++)
                        unlock_page(bp->b_pages[i]);
        }

        if (page_count == bp->b_page_count)
                bp->b_flags |= XBF_DONE;

        return error;
}

/*
 *      Map buffer into kernel address-space if nessecary.
 */
STATIC int
_xfs_buf_map_pages(
        xfs_buf_t               *bp,
        uint                    flags)
{
        /* A single page buffer is always mappable */
        if (bp->b_page_count == 1) {
                bp->b_addr = page_address(bp->b_pages[0]) + bp->b_offset;
                bp->b_flags |= XBF_MAPPED;
        } else if (flags & XBF_MAPPED) {
                if (as_list_len > 64)
                        purge_addresses();
                bp->b_addr = vmap(bp->b_pages, bp->b_page_count,
                                        VM_MAP, PAGE_KERNEL);
                if (unlikely(bp->b_addr == NULL))
                        return -ENOMEM;
                bp->b_addr += bp->b_offset;
                bp->b_flags |= XBF_MAPPED;
        }

        return 0;
}

/*
 *      Finding and Reading Buffers
 */

/*
 *      Look up, and creates if absent, a lockable buffer for
 *      a given range of an inode.  The buffer is returned
 *      locked.  If other overlapping buffers exist, they are
 *      released before the new buffer is created and locked,
 *      which may imply that this call will block until those buffers
 *      are unlocked.  No I/O is implied by this call.
 */
xfs_buf_t *
_xfs_buf_find(
        xfs_buftarg_t           *btp,   /* block device target          */
        xfs_off_t               ioff,   /* starting offset of range     */
        size_t                  isize,  /* length of range              */
        xfs_buf_flags_t         flags,
        xfs_buf_t               *new_bp)
{
        xfs_off_t               range_base;
        size_t                  range_length;
        xfs_bufhash_t           *hash;
        xfs_buf_t               *bp, *n;

        range_base = (ioff << BBSHIFT);
        range_length = (isize << BBSHIFT);

        /* Check for IOs smaller than the sector size / not sector aligned */
        ASSERT(!(range_length < (1 << btp->bt_sshift)));
        ASSERT(!(range_base & (xfs_off_t)btp->bt_smask));

        hash = &btp->bt_hash[hash_long((unsigned long)ioff, btp->bt_hashshift)];

        spin_lock(&hash->bh_lock);

        list_for_each_entry_safe(bp, n, &hash->bh_list, b_hash_list) {
                ASSERT(btp == bp->b_target);
                if (bp->b_file_offset == range_base &&
                    bp->b_buffer_length == range_length) {
                        /*
                         * If we look at something, bring it to the
                         * front of the list for next time.
                         */
                        atomic_inc(&bp->b_hold);
                        list_move(&bp->b_hash_list, &hash->bh_list);
                        goto found;
                }
        }

        /* No match found */
        if (new_bp) {
                _xfs_buf_initialize(new_bp, btp, range_base,
                                range_length, flags);
                new_bp->b_hash = hash;
                list_add(&new_bp->b_hash_list, &hash->bh_list);
        } else {
                XFS_STATS_INC(xb_miss_locked);
        }

        spin_unlock(&hash->bh_lock);
        return new_bp;

found:
        spin_unlock(&hash->bh_lock);

        /* Attempt to get the semaphore without sleeping,
         * if this does not work then we need to drop the
         * spinlock and do a hard attempt on the semaphore.
         */
        if (down_trylock(&bp->b_sema)) {
                if (!(flags & XBF_TRYLOCK)) {
                        /* wait for buffer ownership */
                        xfs_buf_lock(bp);
                        XFS_STATS_INC(xb_get_locked_waited);
                } else {
                        /* We asked for a trylock and failed, no need
                         * to look at file offset and length here, we
                         * know that this buffer at least overlaps our
                         * buffer and is locked, therefore our buffer
                         * either does not exist, or is this buffer.
                         */
                        xfs_buf_rele(bp);
                        XFS_STATS_INC(xb_busy_locked);
                        return NULL;
                }
        } else {
                /* trylock worked */
                XB_SET_OWNER(bp);
        }

        if (bp->b_flags & XBF_STALE) {
                ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
                bp->b_flags &= XBF_MAPPED;
        }

        trace_xfs_buf_find(bp, flags, _RET_IP_);
        XFS_STATS_INC(xb_get_locked);
        return bp;
}

/*
 *      Assembles a buffer covering the specified range.
 *      Storage in memory for all portions of the buffer will be allocated,
 *      although backing storage may not be.
 */
xfs_buf_t *
xfs_buf_get(
        xfs_buftarg_t           *target,/* target for buffer            */
        xfs_off_t               ioff,   /* starting offset of range     */
        size_t                  isize,  /* length of range              */
        xfs_buf_flags_t         flags)
{
        xfs_buf_t               *bp, *new_bp;
        int                     error = 0, i;

        new_bp = xfs_buf_allocate(flags);
        if (unlikely(!new_bp))
                return NULL;

        bp = _xfs_buf_find(target, ioff, isize, flags, new_bp);
        if (bp == new_bp) {
                error = _xfs_buf_lookup_pages(bp, flags);
                if (error)
                        goto no_buffer;
        } else {
                xfs_buf_deallocate(new_bp);
                if (unlikely(bp == NULL))
                        return NULL;
        }

        for (i = 0; i < bp->b_page_count; i++)
                mark_page_accessed(bp->b_pages[i]);

        if (!(bp->b_flags & XBF_MAPPED)) {
                error = _xfs_buf_map_pages(bp, flags);
                if (unlikely(error)) {
                        printk(KERN_WARNING "%s: failed to map pages\n",
                                        __func__);
                        goto no_buffer;
                }
        }

        XFS_STATS_INC(xb_get);

        /*
         * Always fill in the block number now, the mapped cases can do
         * their own overlay of this later.
         */
        bp->b_bn = ioff;
        bp->b_count_desired = bp->b_buffer_length;

        trace_xfs_buf_get(bp, flags, _RET_IP_);
        return bp;

 no_buffer:
        if (flags & (XBF_LOCK | XBF_TRYLOCK))
                xfs_buf_unlock(bp);
        xfs_buf_rele(bp);
        return NULL;
}

STATIC int
_xfs_buf_read(
        xfs_buf_t               *bp,
        xfs_buf_flags_t         flags)
{
        int                     status;

        ASSERT(!(flags & (XBF_DELWRI|XBF_WRITE)));
        ASSERT(bp->b_bn != XFS_BUF_DADDR_NULL);

        bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_DELWRI | \
                        XBF_READ_AHEAD | _XBF_RUN_QUEUES);
        bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | \
                        XBF_READ_AHEAD | _XBF_RUN_QUEUES);

        status = xfs_buf_iorequest(bp);
        if (!status && !(flags & XBF_ASYNC))
                status = xfs_buf_iowait(bp);
        return status;
}

xfs_buf_t *
xfs_buf_read(
        xfs_buftarg_t           *target,
        xfs_off_t               ioff,
        size_t                  isize,
        xfs_buf_flags_t         flags)
{
        xfs_buf_t               *bp;

        flags |= XBF_READ;

        bp = xfs_buf_get(target, ioff, isize, flags);
        if (bp) {
                trace_xfs_buf_read(bp, flags, _RET_IP_);

                if (!XFS_BUF_ISDONE(bp)) {
                        XFS_STATS_INC(xb_get_read);
                        _xfs_buf_read(bp, flags);
                } else if (flags & XBF_ASYNC) {
                        /*
                         * Read ahead call which is already satisfied,
                         * drop the buffer
                         */
                        goto no_buffer;
                } else {
                        /* We do not want read in the flags */
                        bp->b_flags &= ~XBF_READ;
                }
        }

        return bp;

 no_buffer:
        if (flags & (XBF_LOCK | XBF_TRYLOCK))
                xfs_buf_unlock(bp);
        xfs_buf_rele(bp);
        return NULL;
}

/*
 *      If we are not low on memory then do the readahead in a deadlock
 *      safe manner.
 */
void
xfs_buf_readahead(
        xfs_buftarg_t           *target,
        xfs_off_t               ioff,
        size_t                  isize,
        xfs_buf_flags_t         flags)
{
        struct backing_dev_info *bdi;

        bdi = target->bt_mapping->backing_dev_info;
        if (bdi_read_congested(bdi))
                return;

        flags |= (XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD);
        xfs_buf_read(target, ioff, isize, flags);
}

xfs_buf_t *
xfs_buf_get_empty(
        size_t                  len,
        xfs_buftarg_t           *target)
{
        xfs_buf_t               *bp;

        bp = xfs_buf_allocate(0);
        if (bp)
                _xfs_buf_initialize(bp, target, 0, len, 0);
        return bp;
}

static inline struct page *
mem_to_page(
        void                    *addr)
{
        if ((!is_vmalloc_addr(addr))) {
                return virt_to_page(addr);
        } else {
                return vmalloc_to_page(addr);
        }
}

int
xfs_buf_associate_memory(
        xfs_buf_t               *bp,
        void                    *mem,
        size_t                  len)
{
        int                     rval;
        int                     i = 0;
        unsigned long           pageaddr;
        unsigned long           offset;
        size_t                  buflen;
        int                     page_count;

        pageaddr = (unsigned long)mem & PAGE_CACHE_MASK;
        offset = (unsigned long)mem - pageaddr;
        buflen = PAGE_CACHE_ALIGN(len + offset);
        page_count = buflen >> PAGE_CACHE_SHIFT;

        /* Free any previous set of page pointers */
        if (bp->b_pages)
                _xfs_buf_free_pages(bp);

        bp->b_pages = NULL;
        bp->b_addr = mem;

        rval = _xfs_buf_get_pages(bp, page_count, XBF_DONT_BLOCK);
        if (rval)
                return rval;

        bp->b_offset = offset;

        for (i = 0; i < bp->b_page_count; i++) {
                bp->b_pages[i] = mem_to_page((void *)pageaddr);
                pageaddr += PAGE_CACHE_SIZE;
        }

        bp->b_count_desired = len;
        bp->b_buffer_length = buflen;
        bp->b_flags |= XBF_MAPPED;
        bp->b_flags &= ~_XBF_PAGE_LOCKED;

        return 0;
}

xfs_buf_t *
xfs_buf_get_noaddr(
        size_t                  len,
        xfs_buftarg_t           *target)
{
        unsigned long           page_count = PAGE_ALIGN(len) >> PAGE_SHIFT;
        int                     error, i;
        xfs_buf_t               *bp;

        bp = xfs_buf_allocate(0);
        if (unlikely(bp == NULL))
                goto fail;
        _xfs_buf_initialize(bp, target, 0, len, 0);

        error = _xfs_buf_get_pages(bp, page_count, 0);
        if (error)
                goto fail_free_buf;

        for (i = 0; i < page_count; i++) {
                bp->b_pages[i] = alloc_page(GFP_KERNEL);
                if (!bp->b_pages[i])
                        goto fail_free_mem;
        }
        bp->b_flags |= _XBF_PAGES;

        error = _xfs_buf_map_pages(bp, XBF_MAPPED);
        if (unlikely(error)) {
                printk(KERN_WARNING "%s: failed to map pages\n",
                                __func__);
                goto fail_free_mem;
        }

        xfs_buf_unlock(bp);

        trace_xfs_buf_get_noaddr(bp, _RET_IP_);
        return bp;

 fail_free_mem:
        while (--i >= 0)
                __free_page(bp->b_pages[i]);
        _xfs_buf_free_pages(bp);
 fail_free_buf:
        xfs_buf_deallocate(bp);
 fail:
        return NULL;
}

/*
 *      Increment reference count on buffer, to hold the buffer concurrently
 *      with another thread which may release (free) the buffer asynchronously.
 *      Must hold the buffer already to call this function.
 */
void
xfs_buf_hold(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_hold(bp, _RET_IP_);
        atomic_inc(&bp->b_hold);
}

/*
 *      Releases a hold on the specified buffer.  If the
 *      the hold count is 1, calls xfs_buf_free.
 */
void
xfs_buf_rele(
        xfs_buf_t               *bp)
{
        xfs_bufhash_t           *hash = bp->b_hash;

        trace_xfs_buf_rele(bp, _RET_IP_);

        if (unlikely(!hash)) {
                ASSERT(!bp->b_relse);
                if (atomic_dec_and_test(&bp->b_hold))
                        xfs_buf_free(bp);
                return;
        }

        ASSERT(atomic_read(&bp->b_hold) > 0);
        if (atomic_dec_and_lock(&bp->b_hold, &hash->bh_lock)) {
                if (bp->b_relse) {
                        atomic_inc(&bp->b_hold);
                        spin_unlock(&hash->bh_lock);
                        (*(bp->b_relse)) (bp);
                } else if (bp->b_flags & XBF_FS_MANAGED) {
                        spin_unlock(&hash->bh_lock);
                } else {
                        ASSERT(!(bp->b_flags & (XBF_DELWRI|_XBF_DELWRI_Q)));
                        list_del_init(&bp->b_hash_list);
                        spin_unlock(&hash->bh_lock);
                        xfs_buf_free(bp);
                }
        }
}


/*
 *      Mutual exclusion on buffers.  Locking model:
 *
 *      Buffers associated with inodes for which buffer locking
 *      is not enabled are not protected by semaphores, and are
 *      assumed to be exclusively owned by the caller.  There is a
 *      spinlock in the buffer, used by the caller when concurrent
 *      access is possible.
 */

/*
 *      Locks a buffer object, if it is not already locked.
 *      Note that this in no way locks the underlying pages, so it is only
 *      useful for synchronizing concurrent use of buffer objects, not for
 *      synchronizing independent access to the underlying pages.
 */
int
xfs_buf_cond_lock(
        xfs_buf_t               *bp)
{
        int                     locked;

        locked = down_trylock(&bp->b_sema) == 0;
        if (locked)
                XB_SET_OWNER(bp);

        trace_xfs_buf_cond_lock(bp, _RET_IP_);
        return locked ? 0 : -EBUSY;
}

int
xfs_buf_lock_value(
        xfs_buf_t               *bp)
{
        return bp->b_sema.count;
}

/*
 *      Locks a buffer object.
 *      Note that this in no way locks the underlying pages, so it is only
 *      useful for synchronizing concurrent use of buffer objects, not for
 *      synchronizing independent access to the underlying pages.
 */
void
xfs_buf_lock(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_lock(bp, _RET_IP_);

        if (atomic_read(&bp->b_io_remaining))
                blk_run_address_space(bp->b_target->bt_mapping);
        down(&bp->b_sema);
        XB_SET_OWNER(bp);

        trace_xfs_buf_lock_done(bp, _RET_IP_);
}

/*
 *      Releases the lock on the buffer object.
 *      If the buffer is marked delwri but is not queued, do so before we
 *      unlock the buffer as we need to set flags correctly.  We also need to
 *      take a reference for the delwri queue because the unlocker is going to
 *      drop their's and they don't know we just queued it.
 */
void
xfs_buf_unlock(
        xfs_buf_t               *bp)
{
        if ((bp->b_flags & (XBF_DELWRI|_XBF_DELWRI_Q)) == XBF_DELWRI) {
                atomic_inc(&bp->b_hold);
                bp->b_flags |= XBF_ASYNC;
                xfs_buf_delwri_queue(bp, 0);
        }

        XB_CLEAR_OWNER(bp);
        up(&bp->b_sema);

        trace_xfs_buf_unlock(bp, _RET_IP_);
}


/*
 *      Pinning Buffer Storage in Memory
 *      Ensure that no attempt to force a buffer to disk will succeed.
 */
void
xfs_buf_pin(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_pin(bp, _RET_IP_);
        atomic_inc(&bp->b_pin_count);
}

void
xfs_buf_unpin(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_unpin(bp, _RET_IP_);

        if (atomic_dec_and_test(&bp->b_pin_count))
                wake_up_all(&bp->b_waiters);
}

int
xfs_buf_ispin(
        xfs_buf_t               *bp)
{
        return atomic_read(&bp->b_pin_count);
}

STATIC void
xfs_buf_wait_unpin(
        xfs_buf_t               *bp)
{
        DECLARE_WAITQUEUE       (wait, current);

        if (atomic_read(&bp->b_pin_count) == 0)
                return;

        add_wait_queue(&bp->b_waiters, &wait);
        for (;;) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (atomic_read(&bp->b_pin_count) == 0)
                        break;
                if (atomic_read(&bp->b_io_remaining))
                        blk_run_address_space(bp->b_target->bt_mapping);
                schedule();
        }
        remove_wait_queue(&bp->b_waiters, &wait);
        set_current_state(TASK_RUNNING);
}

/*
 *      Buffer Utility Routines
 */

STATIC void
xfs_buf_iodone_work(
        struct work_struct      *work)
{
        xfs_buf_t               *bp =
                container_of(work, xfs_buf_t, b_iodone_work);

        /*
         * We can get an EOPNOTSUPP to ordered writes.  Here we clear the
         * ordered flag and reissue them.  Because we can't tell the higher
         * layers directly that they should not issue ordered I/O anymore, they
         * need to check if the _XFS_BARRIER_FAILED flag was set during I/O completion.
         */
        if ((bp->b_error == EOPNOTSUPP) &&
            (bp->b_flags & (XBF_ORDERED|XBF_ASYNC)) == (XBF_ORDERED|XBF_ASYNC)) {
                trace_xfs_buf_ordered_retry(bp, _RET_IP_);
                bp->b_flags &= ~XBF_ORDERED;
                bp->b_flags |= _XFS_BARRIER_FAILED;
                xfs_buf_iorequest(bp);
        } else if (bp->b_iodone)
                (*(bp->b_iodone))(bp);
        else if (bp->b_flags & XBF_ASYNC)
                xfs_buf_relse(bp);
}

void
xfs_buf_ioend(
        xfs_buf_t               *bp,
        int                     schedule)
{
        trace_xfs_buf_iodone(bp, _RET_IP_);

        bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD);
        if (bp->b_error == 0)
                bp->b_flags |= XBF_DONE;

        if ((bp->b_iodone) || (bp->b_flags & XBF_ASYNC)) {
                if (schedule) {
                        INIT_WORK(&bp->b_iodone_work, xfs_buf_iodone_work);
                        queue_work(xfslogd_workqueue, &bp->b_iodone_work);
                } else {
                        xfs_buf_iodone_work(&bp->b_iodone_work);
                }
        } else {
                complete(&bp->b_iowait);
        }
}

void
xfs_buf_ioerror(
        xfs_buf_t               *bp,
        int                     error)
{
        ASSERT(error >= 0 && error <= 0xffff);
        bp->b_error = (unsigned short)error;
        trace_xfs_buf_ioerror(bp, error, _RET_IP_);
}

int
xfs_bawrite(
        void                    *mp,
        struct xfs_buf          *bp)
{
        trace_xfs_buf_bawrite(bp, _RET_IP_);

        ASSERT(bp->b_bn != XFS_BUF_DADDR_NULL);

        xfs_buf_delwri_dequeue(bp);

        bp->b_flags &= ~(XBF_READ | XBF_DELWRI | XBF_READ_AHEAD);
        bp->b_flags |= (XBF_WRITE | XBF_ASYNC | _XBF_RUN_QUEUES);

        bp->b_mount = mp;
        bp->b_strat = xfs_bdstrat_cb;
        return xfs_bdstrat_cb(bp);
}

void
xfs_bdwrite(
        void                    *mp,
        struct xfs_buf          *bp)
{
        trace_xfs_buf_bdwrite(bp, _RET_IP_);

        bp->b_strat = xfs_bdstrat_cb;
        bp->b_mount = mp;

        bp->b_flags &= ~XBF_READ;
        bp->b_flags |= (XBF_DELWRI | XBF_ASYNC);

        xfs_buf_delwri_queue(bp, 1);
}

STATIC void
_xfs_buf_ioend(
        xfs_buf_t               *bp,
        int                     schedule)
{
        if (atomic_dec_and_test(&bp->b_io_remaining) == 1) {
                bp->b_flags &= ~_XBF_PAGE_LOCKED;
                xfs_buf_ioend(bp, schedule);
        }
}

STATIC void
xfs_buf_bio_end_io(
        struct bio              *bio,
        int                     error)
{
        xfs_buf_t               *bp = (xfs_buf_t *)bio->bi_private;
        unsigned int            blocksize = bp->b_target->bt_bsize;
        struct bio_vec          *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;

        xfs_buf_ioerror(bp, -error);

        do {
                struct page     *page = bvec->bv_page;

                ASSERT(!PagePrivate(page));
                if (unlikely(bp->b_error)) {
                        if (bp->b_flags & XBF_READ)
                                ClearPageUptodate(page);
                } else if (blocksize >= PAGE_CACHE_SIZE) {
                        SetPageUptodate(page);
                } else if (!PagePrivate(page) &&
                                (bp->b_flags & _XBF_PAGE_CACHE)) {
                        set_page_region(page, bvec->bv_offset, bvec->bv_len);
                }

                if (--bvec >= bio->bi_io_vec)
                        prefetchw(&bvec->bv_page->flags);

                if (bp->b_flags & _XBF_PAGE_LOCKED)
                        unlock_page(page);
        } while (bvec >= bio->bi_io_vec);

        _xfs_buf_ioend(bp, 1);
        bio_put(bio);
}

STATIC void
_xfs_buf_ioapply(
        xfs_buf_t               *bp)
{
        int                     rw, map_i, total_nr_pages, nr_pages;
        struct bio              *bio;
        int                     offset = bp->b_offset;
        int                     size = bp->b_count_desired;
        sector_t                sector = bp->b_bn;
        unsigned int            blocksize = bp->b_target->bt_bsize;

        total_nr_pages = bp->b_page_count;
        map_i = 0;

        if (bp->b_flags & XBF_ORDERED) {
                ASSERT(!(bp->b_flags & XBF_READ));
                rw = WRITE_BARRIER;
        } else if (bp->b_flags & XBF_LOG_BUFFER) {
                ASSERT(!(bp->b_flags & XBF_READ_AHEAD));
                bp->b_flags &= ~_XBF_RUN_QUEUES;
                rw = (bp->b_flags & XBF_WRITE) ? WRITE_SYNC : READ_SYNC;
        } else if (bp->b_flags & _XBF_RUN_QUEUES) {
                ASSERT(!(bp->b_flags & XBF_READ_AHEAD));
                bp->b_flags &= ~_XBF_RUN_QUEUES;
                rw = (bp->b_flags & XBF_WRITE) ? WRITE_META : READ_META;
        } else {
                rw = (bp->b_flags & XBF_WRITE) ? WRITE :
                     (bp->b_flags & XBF_READ_AHEAD) ? READA : READ;
        }

        /* Special code path for reading a sub page size buffer in --
         * we populate up the whole page, and hence the other metadata
         * in the same page.  This optimization is only valid when the
         * filesystem block size is not smaller than the page size.
         */
        if ((bp->b_buffer_length < PAGE_CACHE_SIZE) &&
            ((bp->b_flags & (XBF_READ|_XBF_PAGE_LOCKED)) ==
              (XBF_READ|_XBF_PAGE_LOCKED)) &&
            (blocksize >= PAGE_CACHE_SIZE)) {
                bio = bio_alloc(GFP_NOIO, 1);

                bio->bi_bdev = bp->b_target->bt_bdev;
                bio->bi_sector = sector - (offset >> BBSHIFT);
                bio->bi_end_io = xfs_buf_bio_end_io;
                bio->bi_private = bp;

                bio_add_page(bio, bp->b_pages[0], PAGE_CACHE_SIZE, 0);
                size = 0;

                atomic_inc(&bp->b_io_remaining);

                goto submit_io;
        }

next_chunk:
        atomic_inc(&bp->b_io_remaining);
        nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);
        if (nr_pages > total_nr_pages)
                nr_pages = total_nr_pages;

        bio = bio_alloc(GFP_NOIO, nr_pages);
        bio->bi_bdev = bp->b_target->bt_bdev;
        bio->bi_sector = sector;
        bio->bi_end_io = xfs_buf_bio_end_io;
        bio->bi_private = bp;

        for (; size && nr_pages; nr_pages--, map_i++) {
                int     rbytes, nbytes = PAGE_CACHE_SIZE - offset;

                if (nbytes > size)
                        nbytes = size;

                rbytes = bio_add_page(bio, bp->b_pages[map_i], nbytes, offset);
                if (rbytes < nbytes)
                        break;

                offset = 0;
                sector += nbytes >> BBSHIFT;
                size -= nbytes;
                total_nr_pages--;
        }

submit_io:
        if (likely(bio->bi_size)) {
                submit_bio(rw, bio);
                if (size)
                        goto next_chunk;
        } else {
                bio_put(bio);
                xfs_buf_ioerror(bp, EIO);
        }
}

int
xfs_buf_iorequest(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_iorequest(bp, _RET_IP_);

        if (bp->b_flags & XBF_DELWRI) {
                xfs_buf_delwri_queue(bp, 1);
                return 0;
        }

        if (bp->b_flags & XBF_WRITE) {
                xfs_buf_wait_unpin(bp);
        }

        xfs_buf_hold(bp);

        /* Set the count to 1 initially, this will stop an I/O
         * completion callout which happens before we have started
         * all the I/O from calling xfs_buf_ioend too early.
         */
        atomic_set(&bp->b_io_remaining, 1);
        _xfs_buf_ioapply(bp);
        _xfs_buf_ioend(bp, 0);

        xfs_buf_rele(bp);
        return 0;
}

/*
 *      Waits for I/O to complete on the buffer supplied.
 *      It returns immediately if no I/O is pending.
 *      It returns the I/O error code, if any, or 0 if there was no error.
 */
int
xfs_buf_iowait(
        xfs_buf_t               *bp)
{
        trace_xfs_buf_iowait(bp, _RET_IP_);

        if (atomic_read(&bp->b_io_remaining))
                blk_run_address_space(bp->b_target->bt_mapping);
        wait_for_completion(&bp->b_iowait);

        trace_xfs_buf_iowait_done(bp, _RET_IP_);
        return bp->b_error;
}

xfs_caddr_t
xfs_buf_offset(
        xfs_buf_t               *bp,
        size_t                  offset)
{
        struct page             *page;

        if (bp->b_flags & XBF_MAPPED)
                return XFS_BUF_PTR(bp) + offset;

        offset += bp->b_offset;
        page = bp->b_pages[offset >> PAGE_CACHE_SHIFT];
        return (xfs_caddr_t)page_address(page) + (offset & (PAGE_CACHE_SIZE-1));
}

/*
 *      Move data into or out of a buffer.
 */
void
xfs_buf_iomove(
        xfs_buf_t               *bp,    /* buffer to process            */
        size_t                  boff,   /* starting buffer offset       */
        size_t                  bsize,  /* length to copy               */
        caddr_t                 data,   /* data address                 */
        xfs_buf_rw_t            mode)   /* read/write/zero flag         */
{
        size_t                  bend, cpoff, csize;
        struct page             *page;

        bend = boff + bsize;
        while (boff < bend) {
                page = bp->b_pages[xfs_buf_btoct(boff + bp->b_offset)];
                cpoff = xfs_buf_poff(boff + bp->b_offset);
                csize = min_t(size_t,
                              PAGE_CACHE_SIZE-cpoff, bp->b_count_desired-boff);

                ASSERT(((csize + cpoff) <= PAGE_CACHE_SIZE));

                switch (mode) {
                case XBRW_ZERO:
                        memset(page_address(page) + cpoff, 0, csize);
                        break;
                case XBRW_READ:
                        memcpy(data, page_address(page) + cpoff, csize);
                        break;
                case XBRW_WRITE:
                        memcpy(page_address(page) + cpoff, data, csize);
                }

                boff += csize;
                data += csize;
        }
}

/*
 *      Handling of buffer targets (buftargs).
 */

/*
 *      Wait for any bufs with callbacks that have been submitted but
 *      have not yet returned... walk the hash list for the target.
 */
void
xfs_wait_buftarg(
        xfs_buftarg_t   *btp)
{
        xfs_buf_t       *bp, *n;
        xfs_bufhash_t   *hash;
        uint            i;

        for (i = 0; i < (1 << btp->bt_hashshift); i++) {
                hash = &btp->bt_hash[i];
again:
                spin_lock(&hash->bh_lock);
                list_for_each_entry_safe(bp, n, &hash->bh_list, b_hash_list) {
                        ASSERT(btp == bp->b_target);
                        if (!(bp->b_flags & XBF_FS_MANAGED)) {
                                spin_unlock(&hash->bh_lock);
                                /*
                                 * Catch superblock reference count leaks
                                 * immediately
                                 */
                                BUG_ON(bp->b_bn == 0);
                                delay(100);
                                goto again;
                        }
                }
                spin_unlock(&hash->bh_lock);
        }
}

/*
 *      Allocate buffer hash table for a given target.
 *      For devices containing metadata (i.e. not the log/realtime devices)
 *      we need to allocate a much larger hash table.
 */
STATIC void
xfs_alloc_bufhash(
        xfs_buftarg_t           *btp,
        int                     external)
{
        unsigned int            i;

        btp->bt_hashshift = external ? 3 : 8;   /* 8 or 256 buckets */
        btp->bt_hashmask = (1 << btp->bt_hashshift) - 1;
        btp->bt_hash = kmem_zalloc((1 << btp->bt_hashshift) *
                                        sizeof(xfs_bufhash_t), KM_SLEEP | KM_LARGE);
        for (i = 0; i < (1 << btp->bt_hashshift); i++) {
                spin_lock_init(&btp->bt_hash[i].bh_lock);
                INIT_LIST_HEAD(&btp->bt_hash[i].bh_list);
        }
}

STATIC void
xfs_free_bufhash(
        xfs_buftarg_t           *btp)
{
        kmem_free(btp->bt_hash);
        btp->bt_hash = NULL;
}

/*
 *      buftarg list for delwrite queue processing
 */
static LIST_HEAD(xfs_buftarg_list);
static DEFINE_SPINLOCK(xfs_buftarg_lock);

STATIC void
xfs_register_buftarg(
        xfs_buftarg_t           *btp)
{
        spin_lock(&xfs_buftarg_lock);
        list_add(&btp->bt_list, &xfs_buftarg_list);
        spin_unlock(&xfs_buftarg_lock);
}

STATIC void
xfs_unregister_buftarg(
        xfs_buftarg_t           *btp)
{
        spin_lock(&xfs_buftarg_lock);
        list_del(&btp->bt_list);
        spin_unlock(&xfs_buftarg_lock);
}

void
xfs_free_buftarg(
        struct xfs_mount        *mp,
        struct xfs_buftarg      *btp)
{
        xfs_flush_buftarg(btp, 1);
        if (mp->m_flags & XFS_MOUNT_BARRIER)
                xfs_blkdev_issue_flush(btp);
        xfs_free_bufhash(btp);
        iput(btp->bt_mapping->host);

        /* Unregister the buftarg first so that we don't get a
         * wakeup finding a non-existent task
         */
        xfs_unregister_buftarg(btp);
        kthread_stop(btp->bt_task);

        kmem_free(btp);
}

STATIC int
xfs_setsize_buftarg_flags(
        xfs_buftarg_t           *btp,
        unsigned int            blocksize,
        unsigned int            sectorsize,
        int                     verbose)
{
        btp->bt_bsize = blocksize;
        btp->bt_sshift = ffs(sectorsize) - 1;
        btp->bt_smask = sectorsize - 1;

        if (set_blocksize(btp->bt_bdev, sectorsize)) {
                printk(KERN_WARNING
                        "XFS: Cannot set_blocksize to %u on device %s\n",
                        sectorsize, XFS_BUFTARG_NAME(btp));
                return EINVAL;
        }

        if (verbose &&
            (PAGE_CACHE_SIZE / BITS_PER_LONG) > sectorsize) {
                printk(KERN_WARNING
                        "XFS: %u byte sectors in use on device %s.  "
                        "This is suboptimal; %u or greater is ideal.\n",
                        sectorsize, XFS_BUFTARG_NAME(btp),
                        (unsigned int)PAGE_CACHE_SIZE / BITS_PER_LONG);
        }

        return 0;
}

/*
 *      When allocating the initial buffer target we have not yet
 *      read in the superblock, so don't know what sized sectors
 *      are being used is at this early stage.  Play safe.
 */
STATIC int
xfs_setsize_buftarg_early(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        return xfs_setsize_buftarg_flags(btp,
                        PAGE_CACHE_SIZE, bdev_logical_block_size(bdev), 0);
}

int
xfs_setsize_buftarg(
        xfs_buftarg_t           *btp,
        unsigned int            blocksize,
        unsigned int            sectorsize)
{
        return xfs_setsize_buftarg_flags(btp, blocksize, sectorsize, 1);
}

STATIC int
xfs_mapping_buftarg(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        struct backing_dev_info *bdi;
        struct inode            *inode;
        struct address_space    *mapping;
        static const struct address_space_operations mapping_aops = {
                .sync_page = block_sync_page,
                .migratepage = fail_migrate_page,
        };

        inode = new_inode(bdev->bd_inode->i_sb);
        if (!inode) {
                printk(KERN_WARNING
                        "XFS: Cannot allocate mapping inode for device %s\n",
                        XFS_BUFTARG_NAME(btp));
                return ENOMEM;
        }
        inode->i_mode = S_IFBLK;
        inode->i_bdev = bdev;
        inode->i_rdev = bdev->bd_dev;
        bdi = blk_get_backing_dev_info(bdev);
        if (!bdi)
                bdi = &default_backing_dev_info;
        mapping = &inode->i_data;
        mapping->a_ops = &mapping_aops;
        mapping->backing_dev_info = bdi;
        mapping_set_gfp_mask(mapping, GFP_NOFS);
        btp->bt_mapping = mapping;
        return 0;
}

STATIC int
xfs_alloc_delwrite_queue(
        xfs_buftarg_t           *btp)
{
        int     error = 0;

        INIT_LIST_HEAD(&btp->bt_list);
        INIT_LIST_HEAD(&btp->bt_delwrite_queue);
        spin_lock_init(&btp->bt_delwrite_lock);
        btp->bt_flags = 0;
        btp->bt_task = kthread_run(xfsbufd, btp, "xfsbufd");
        if (IS_ERR(btp->bt_task)) {
                error = PTR_ERR(btp->bt_task);
                goto out_error;
        }
        xfs_register_buftarg(btp);
out_error:
        return error;
}

xfs_buftarg_t *
xfs_alloc_buftarg(
        struct block_device     *bdev,
        int                     external)
{
        xfs_buftarg_t           *btp;

        btp = kmem_zalloc(sizeof(*btp), KM_SLEEP);

        btp->bt_dev =  bdev->bd_dev;
        btp->bt_bdev = bdev;
        if (xfs_setsize_buftarg_early(btp, bdev))
                goto error;
        if (xfs_mapping_buftarg(btp, bdev))
                goto error;
        if (xfs_alloc_delwrite_queue(btp))
                goto error;
        xfs_alloc_bufhash(btp, external);
        return btp;

error:
        kmem_free(btp);
        return NULL;
}


/*
 *      Delayed write buffer handling
 */
STATIC void
xfs_buf_delwri_queue(
        xfs_buf_t               *bp,
        int                     unlock)
{
        struct list_head        *dwq = &bp->b_target->bt_delwrite_queue;
        spinlock_t              *dwlk = &bp->b_target->bt_delwrite_lock;

        trace_xfs_buf_delwri_queue(bp, _RET_IP_);

        ASSERT((bp->b_flags&(XBF_DELWRI|XBF_ASYNC)) == (XBF_DELWRI|XBF_ASYNC));

        spin_lock(dwlk);
        /* If already in the queue, dequeue and place at tail */
        if (!list_empty(&bp->b_list)) {
                ASSERT(bp->b_flags & _XBF_DELWRI_Q);
                if (unlock)
                        atomic_dec(&bp->b_hold);
                list_del(&bp->b_list);
        }

        bp->b_flags |= _XBF_DELWRI_Q;
        list_add_tail(&bp->b_list, dwq);
        bp->b_queuetime = jiffies;
        spin_unlock(dwlk);

        if (unlock)
                xfs_buf_unlock(bp);
}

void
xfs_buf_delwri_dequeue(
        xfs_buf_t               *bp)
{
        spinlock_t              *dwlk = &bp->b_target->bt_delwrite_lock;
        int                     dequeued = 0;

        spin_lock(dwlk);
        if ((bp->b_flags & XBF_DELWRI) && !list_empty(&bp->b_list)) {
                ASSERT(bp->b_flags & _XBF_DELWRI_Q);
                list_del_init(&bp->b_list);
                dequeued = 1;
        }
        bp->b_flags &= ~(XBF_DELWRI|_XBF_DELWRI_Q);
        spin_unlock(dwlk);

        if (dequeued)
                xfs_buf_rele(bp);

        trace_xfs_buf_delwri_dequeue(bp, _RET_IP_);
}

STATIC void
xfs_buf_runall_queues(
        struct workqueue_struct *queue)
{
        flush_workqueue(queue);
}

STATIC int
xfsbufd_wakeup(
        int                     priority,
        gfp_t                   mask)
{
        xfs_buftarg_t           *btp;

        spin_lock(&xfs_buftarg_lock);
        list_for_each_entry(btp, &xfs_buftarg_list, bt_list) {
                if (test_bit(XBT_FORCE_SLEEP, &btp->bt_flags))
                        continue;
                set_bit(XBT_FORCE_FLUSH, &btp->bt_flags);
                wake_up_process(btp->bt_task);
        }
        spin_unlock(&xfs_buftarg_lock);
        return 0;
}

/*
 * Move as many buffers as specified to the supplied list
 * idicating if we skipped any buffers to prevent deadlocks.
 */
STATIC int
xfs_buf_delwri_split(
        xfs_buftarg_t   *target,
        struct list_head *list,
        unsigned long   age)
{
        xfs_buf_t       *bp, *n;
        struct list_head *dwq = &target->bt_delwrite_queue;
        spinlock_t      *dwlk = &target->bt_delwrite_lock;
        int             skipped = 0;
        int             force;

        force = test_and_clear_bit(XBT_FORCE_FLUSH, &target->bt_flags);
        INIT_LIST_HEAD(list);
        spin_lock(dwlk);
        list_for_each_entry_safe(bp, n, dwq, b_list) {
                trace_xfs_buf_delwri_split(bp, _RET_IP_);
                ASSERT(bp->b_flags & XBF_DELWRI);

                if (!xfs_buf_ispin(bp) && !xfs_buf_cond_lock(bp)) {
                        if (!force &&
                            time_before(jiffies, bp->b_queuetime + age)) {
                                xfs_buf_unlock(bp);
                                break;
                        }

                        bp->b_flags &= ~(XBF_DELWRI|_XBF_DELWRI_Q|
                                         _XBF_RUN_QUEUES);
                        bp->b_flags |= XBF_WRITE;
                        list_move_tail(&bp->b_list, list);
                } else
                        skipped++;
        }
        spin_unlock(dwlk);

        return skipped;

}

STATIC int
xfsbufd(
        void            *data)
{
        struct list_head tmp;
        xfs_buftarg_t   *target = (xfs_buftarg_t *)data;
        int             count;
        xfs_buf_t       *bp;

        current->flags |= PF_MEMALLOC;

        set_freezable();

        do {
                if (unlikely(freezing(current))) {
                        set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                        refrigerator();
                } else {
                        clear_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                }

                schedule_timeout_interruptible(
                        xfs_buf_timer_centisecs * msecs_to_jiffies(10));

                xfs_buf_delwri_split(target, &tmp,
                                xfs_buf_age_centisecs * msecs_to_jiffies(10));

                count = 0;
                while (!list_empty(&tmp)) {
                        bp = list_entry(tmp.next, xfs_buf_t, b_list);
                        ASSERT(target == bp->b_target);

                        list_del_init(&bp->b_list);
                        xfs_buf_iostrategy(bp);
                        count++;
                }

                if (as_list_len > 0)
                        purge_addresses();
                if (count)
                        blk_run_address_space(target->bt_mapping);

        } while (!kthread_should_stop());

        return 0;
}

/*
 *      Go through all incore buffers, and release buffers if they belong to
 *      the given device. This is used in filesystem error handling to
 *      preserve the consistency of its metadata.
 */
int
xfs_flush_buftarg(
        xfs_buftarg_t   *target,
        int             wait)
{
        struct list_head tmp;
        xfs_buf_t       *bp, *n;
        int             pincount = 0;

        xfs_buf_runall_queues(xfsconvertd_workqueue);
        xfs_buf_runall_queues(xfsdatad_workqueue);
        xfs_buf_runall_queues(xfslogd_workqueue);

        set_bit(XBT_FORCE_FLUSH, &target->bt_flags);
        pincount = xfs_buf_delwri_split(target, &tmp, 0);

        /*
         * Dropped the delayed write list lock, now walk the temporary list
         */
        list_for_each_entry_safe(bp, n, &tmp, b_list) {
                ASSERT(target == bp->b_target);
                if (wait)
                        bp->b_flags &= ~XBF_ASYNC;
                else
                        list_del_init(&bp->b_list);

                xfs_buf_iostrategy(bp);
        }

        if (wait)
                blk_run_address_space(target->bt_mapping);

        /*
         * Remaining list items must be flushed before returning
         */
        while (!list_empty(&tmp)) {
                bp = list_entry(tmp.next, xfs_buf_t, b_list);

                list_del_init(&bp->b_list);
                xfs_iowait(bp);
                xfs_buf_relse(bp);
        }

        return pincount;
}

int __init
xfs_buf_init(void)
{
        xfs_buf_zone = kmem_zone_init_flags(sizeof(xfs_buf_t), "xfs_buf",
                                                KM_ZONE_HWALIGN, NULL);
        if (!xfs_buf_zone)
                goto out;

        xfslogd_workqueue = create_workqueue("xfslogd");
        if (!xfslogd_workqueue)
                goto out_free_buf_zone;

        xfsdatad_workqueue = create_workqueue("xfsdatad");
        if (!xfsdatad_workqueue)
                goto out_destroy_xfslogd_workqueue;

        xfsconvertd_workqueue = create_workqueue("xfsconvertd");
        if (!xfsconvertd_workqueue)
                goto out_destroy_xfsdatad_workqueue;

        register_shrinker(&xfs_buf_shake);
        return 0;

 out_destroy_xfsdatad_workqueue:
        destroy_workqueue(xfsdatad_workqueue);
 out_destroy_xfslogd_workqueue:
        destroy_workqueue(xfslogd_workqueue);
 out_free_buf_zone:
        kmem_zone_destroy(xfs_buf_zone);
 out:
        return -ENOMEM;
}

void
xfs_buf_terminate(void)
{
        unregister_shrinker(&xfs_buf_shake);
        destroy_workqueue(xfsconvertd_workqueue);
        destroy_workqueue(xfsdatad_workqueue);
        destroy_workqueue(xfslogd_workqueue);
        kmem_zone_destroy(xfs_buf_zone);
}

#ifdef CONFIG_KDB_MODULES
struct list_head *
xfs_get_buftarg_list(void)
{
        return &xfs_buftarg_list;
}
#endif