text: /*
   * 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/gfp.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 <linux/list_sort.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));
  
  static inline int
  xfs_buf_is_vmapped(
  	struct xfs_buf	*bp)
  {
  	/*
  	 * Return true if the buffer is vmapped.
  	 *
  	 * The XBF_MAPPED flag is set if the buffer should be mapped, but the
  	 * code is clever enough to know it doesn't have to map a single page,
  	 * so the check has to be both for XBF_MAPPED and bp->b_page_count > 1.
  	 */
  	return (bp->b_flags & XBF_MAPPED) && bp->b_page_count > 1;
  }
  
  static inline int
  xfs_buf_vmap_len(
  	struct xfs_buf	*bp)
  {
  	return (bp->b_page_count * PAGE_SIZE) - bp->b_offset;
  }
  
  /*
   *	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);
  }
  
  /*
   *	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);
  		bp->b_pages = NULL;
  	}
  }
  
  /*
   *	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 (xfs_buf_is_vmapped(bp))
  			vm_unmap_ram(bp->b_addr - bp->b_offset,
  					bp->b_page_count);
  
  		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) {
  		bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
  					-1, 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_bwrite(
  	struct xfs_mount	*mp,
  	struct xfs_buf		*bp)
  {
  	int			iowait = (bp->b_flags & XBF_ASYNC) == 0;
  	int			error = 0;
  
  	bp->b_strat = xfs_bdstrat_cb;
  	bp->b_mount = mp;
  	bp->b_flags |= XBF_WRITE;
  	if (!iowait)
  		bp->b_flags |= _XBF_RUN_QUEUES;
  
  	xfs_buf_delwri_dequeue(bp);
  	xfs_buf_iostrategy(bp);
  
  	if (iowait) {
  		error = xfs_buf_iowait(bp);
  		if (error)
  			xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
  		xfs_buf_relse(bp);
  	}
  
  	return error;
  }
  
  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);
  }
  
  /*
   * Called when we want to stop a buffer from getting written or read.
   * We attach the EIO error, muck with its flags, and call biodone
   * so that the proper iodone callbacks get called.
   */
  STATIC int
  xfs_bioerror(
  	xfs_buf_t *bp)
  {
  #ifdef XFSERRORDEBUG
  	ASSERT(XFS_BUF_ISREAD(bp) || bp->b_iodone);
  #endif
  
  	/*
  	 * No need to wait until the buffer is unpinned, we aren't flushing it.
  	 */
  	XFS_BUF_ERROR(bp, EIO);
  
  	/*
  	 * We're calling biodone, so delete XBF_DONE flag.
  	 */
  	XFS_BUF_UNREAD(bp);
  	XFS_BUF_UNDELAYWRITE(bp);
  	XFS_BUF_UNDONE(bp);
  	XFS_BUF_STALE(bp);
  
  	XFS_BUF_CLR_BDSTRAT_FUNC(bp);
  	xfs_biodone(bp);
  
  	return EIO;
  }
  
  /*
   * Same as xfs_bioerror, except that we are releasing the buffer
   * here ourselves, and avoiding the biodone call.
   * This is meant for userdata errors; metadata bufs come with
   * iodone functions attached, so that we can track down errors.
   */
  STATIC int
  xfs_bioerror_relse(
  	struct xfs_buf	*bp)
  {
  	int64_t		fl = XFS_BUF_BFLAGS(bp);
  	/*
  	 * No need to wait until the buffer is unpinned.
  	 * We aren't flushing it.
  	 *
  	 * chunkhold expects B_DONE to be set, whether
  	 * we actually finish the I/O or not. We don't want to
  	 * change that interface.
  	 */
  	XFS_BUF_UNREAD(bp);
  	XFS_BUF_UNDELAYWRITE(bp);
  	XFS_BUF_DONE(bp);
  	XFS_BUF_STALE(bp);
  	XFS_BUF_CLR_IODONE_FUNC(bp);
  	XFS_BUF_CLR_BDSTRAT_FUNC(bp);
  	if (!(fl & XBF_ASYNC)) {
  		/*
  		 * Mark b_error and B_ERROR _both_.
  		 * Lot's of chunkcache code assumes that.
  		 * There's no reason to mark error for
  		 * ASYNC buffers.
  		 */
  		XFS_BUF_ERROR(bp, EIO);
  		XFS_BUF_FINISH_IOWAIT(bp);
  	} else {
  		xfs_buf_relse(bp);
  	}
  
  	return EIO;
  }
  
  
  /*
   * All xfs metadata buffers except log state machine buffers
   * get this attached as their b_bdstrat callback function.
   * This is so that we can catch a buffer
   * after prematurely unpinning it to forcibly shutdown the filesystem.
   */
  int
  xfs_bdstrat_cb(
  	struct xfs_buf	*bp)
  {
  	if (XFS_FORCED_SHUTDOWN(bp->b_mount)) {
  		trace_xfs_bdstrat_shut(bp, _RET_IP_);
  		/*
  		 * Metadata write that didn't get logged but
  		 * written delayed anyway. These aren't associated
  		 * with a transaction, and can be ignored.
  		 */
  		if (!bp->b_iodone && !XFS_BUF_ISREAD(bp))
  			return xfs_bioerror_relse(bp);
  		else
  			return xfs_bioerror(bp);
  	}
  
  	xfs_buf_iorequest(bp);
  	return 0;
  }
  
  /*
   * Wrapper around bdstrat so that we can stop data from going to disk in case
   * we are shutting down the filesystem.  Typically user data goes thru this
   * path; one of the exceptions is the superblock.
   */
  void
  xfsbdstrat(
  	struct xfs_mount	*mp,
  	struct xfs_buf		*bp)
  {
  	if (XFS_FORCED_SHUTDOWN(mp)) {
  		trace_xfs_bdstrat_shut(bp, _RET_IP_);
  		xfs_bioerror_relse(bp);
  		return;
  	}
  
  	xfs_buf_iorequest(bp);
  }
  
  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);
  
  	if (!error && xfs_buf_is_vmapped(bp) && (bp->b_flags & XBF_READ))
  		invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
  
  	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)) {
  		if (xfs_buf_is_vmapped(bp)) {
  			flush_kernel_vmap_range(bp->b_addr,
  						xfs_buf_vmap_len(bp));
  		}
  		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		*/
  	void			*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_large((1 << btp->bt_hashshift) *
  					 sizeof(xfs_bufhash_t));
  	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_large(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);
  	}
  
  	if (list_empty(dwq)) {
  		/* start xfsbufd as it is about to have something to do */
  		wake_up_process(bp->b_target->bt_task);
  	}
  
  	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_);
  }
  
  /*
   * If a delwri buffer needs to be pushed before it has aged out, then promote
   * it to the head of the delwri queue so that it will be flushed on the next
   * xfsbufd run. We do this by resetting the queuetime of the buffer to be older
   * than the age currently needed to flush the buffer. Hence the next time the
   * xfsbufd sees it is guaranteed to be considered old enough to flush.
   */
  void
  xfs_buf_delwri_promote(
  	struct xfs_buf	*bp)
  {
  	struct xfs_buftarg *btp = bp->b_target;
  	long		age = xfs_buf_age_centisecs * msecs_to_jiffies(10) + 1;
  
  	ASSERT(bp->b_flags & XBF_DELWRI);
  	ASSERT(bp->b_flags & _XBF_DELWRI_Q);
  
  	/*
  	 * Check the buffer age before locking the delayed write queue as we
  	 * don't need to promote buffers that are already past the flush age.
  	 */
  	if (bp->b_queuetime < jiffies - age)
  		return;
  	bp->b_queuetime = jiffies - age;
  	spin_lock(&btp->bt_delwrite_lock);
  	list_move(&bp->b_list, &btp->bt_delwrite_queue);
  	spin_unlock(&btp->bt_delwrite_lock);
  }
  
  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;
  		if (list_empty(&btp->bt_delwrite_queue))
  			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;
  
  }
  
  /*
   * Compare function is more complex than it needs to be because
   * the return value is only 32 bits and we are doing comparisons
   * on 64 bit values
   */
  static int
  xfs_buf_cmp(
  	void		*priv,
  	struct list_head *a,
  	struct list_head *b)
  {
  	struct xfs_buf	*ap = container_of(a, struct xfs_buf, b_list);
  	struct xfs_buf	*bp = container_of(b, struct xfs_buf, b_list);
  	xfs_daddr_t		diff;
  
  	diff = ap->b_bn - bp->b_bn;
  	if (diff < 0)
  		return -1;
  	if (diff > 0)
  		return 1;
  	return 0;
  }
  
  void
  xfs_buf_delwri_sort(
  	xfs_buftarg_t	*target,
  	struct list_head *list)
  {
  	list_sort(NULL, list, xfs_buf_cmp);
  }
  
  STATIC int
  xfsbufd(
  	void		*data)
  {
  	xfs_buftarg_t   *target = (xfs_buftarg_t *)data;
  
  	current->flags |= PF_MEMALLOC;
  
  	set_freezable();
  
  	do {
  		long	age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
  		long	tout = xfs_buf_timer_centisecs * msecs_to_jiffies(10);
  		int	count = 0;
  		struct list_head tmp;
  
  		if (unlikely(freezing(current))) {
  			set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
  			refrigerator();
  		} else {
  			clear_bit(XBT_FORCE_SLEEP, &target->bt_flags);
  		}
  
  		/* sleep for a long time if there is nothing to do. */
  		if (list_empty(&target->bt_delwrite_queue))
  			tout = MAX_SCHEDULE_TIMEOUT;
  		schedule_timeout_interruptible(tout);
  
  		xfs_buf_delwri_split(target, &tmp, age);
  		list_sort(NULL, &tmp, xfs_buf_cmp);
  		while (!list_empty(&tmp)) {
  			struct xfs_buf *bp;
  			bp = list_first_entry(&tmp, struct xfs_buf, b_list);
  			list_del_init(&bp->b_list);
  			xfs_buf_iostrategy(bp);
  			count++;
  		}
  		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)
  {
  	xfs_buf_t	*bp;
  	int		pincount = 0;
  	LIST_HEAD(tmp_list);
  	LIST_HEAD(wait_list);
  
  	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_list, 0);
  
  	/*
  	 * Dropped the delayed write list lock, now walk the temporary list.
  	 * All I/O is issued async and then if we need to wait for completion
  	 * we do that after issuing all the IO.
  	 */
  	list_sort(NULL, &tmp_list, xfs_buf_cmp);
  	while (!list_empty(&tmp_list)) {
  		bp = list_first_entry(&tmp_list, struct xfs_buf, b_list);
  		ASSERT(target == bp->b_target);
  		list_del_init(&bp->b_list);
  		if (wait) {
  			bp->b_flags &= ~XBF_ASYNC;
  			list_add(&bp->b_list, &wait_list);
  		}
  		xfs_buf_iostrategy(bp);
  	}
  
  	if (wait) {
  		/* Expedite and wait for IO to complete. */
  		blk_run_address_space(target->bt_mapping);
  		while (!list_empty(&wait_list)) {
  			bp = list_first_entry(&wait_list, struct xfs_buf, 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
  