linux-vybrid_public/fs/xfs/linux-2.6/xfs_buf.c

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.  All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2 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.
 *
 * Further, this software is distributed without any warranty that it is
 * free of the rightful claim of any third person regarding infringement
 * or the like.  Any license provided herein, whether implied or
 * otherwise, applies only to this software file.  Patent licenses, if
 * any, provided herein do not apply to combinations of this program with
 * other software, or any other product whatsoever.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write the Free Software Foundation, Inc., 59
 * Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
 * Mountain View, CA  94043, or:
 *
 * http://www.sgi.com
 *
 * For further information regarding this notice, see:
 *
 * http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
 */

/*
 *	The xfs_buf.c code provides an abstract buffer cache model on top
 *	of the Linux page cache.  Cached metadata blocks for a file system
 *	are hashed to the inode for the block device.  xfs_buf.c assembles
 *	buffers (xfs_buf_t) on demand to aggregate such cached pages for I/O.
 *
 *      Written by Steve Lord, Jim Mostek, Russell Cattelan
 *		    and Rajagopal Ananthanarayanan ("ananth") at SGI.
 *
 */

#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 "xfs_linux.h"

/*
 * File wide globals
 */

STATIC kmem_cache_t *pagebuf_zone;
STATIC kmem_shaker_t pagebuf_shake;
STATIC int xfsbufd_wakeup(int, gfp_t);
STATIC void pagebuf_delwri_queue(xfs_buf_t *, int);

STATIC struct workqueue_struct *xfslogd_workqueue;
struct workqueue_struct *xfsdatad_workqueue;

/*
 * Pagebuf debugging
 */

#ifdef PAGEBUF_TRACE
void
pagebuf_trace(
	xfs_buf_t	*pb,
	char		*id,
	void		*data,
	void		*ra)
{
	ktrace_enter(pagebuf_trace_buf,
		pb, id,
		(void *)(unsigned long)pb->pb_flags,
		(void *)(unsigned long)pb->pb_hold.counter,
		(void *)(unsigned long)pb->pb_sema.count.counter,
		(void *)current,
		data, ra,
		(void *)(unsigned long)((pb->pb_file_offset>>32) & 0xffffffff),
		(void *)(unsigned long)(pb->pb_file_offset & 0xffffffff),
		(void *)(unsigned long)pb->pb_buffer_length,
		NULL, NULL, NULL, NULL, NULL);
}
ktrace_t *pagebuf_trace_buf;
#define PAGEBUF_TRACE_SIZE	4096
#define PB_TRACE(pb, id, data)	\
	pagebuf_trace(pb, id, (void *)data, (void *)__builtin_return_address(0))
#else
#define PB_TRACE(pb, id, data)	do { } while (0)
#endif

#ifdef PAGEBUF_LOCK_TRACKING
# define PB_SET_OWNER(pb)	((pb)->pb_last_holder = current->pid)
# define PB_CLEAR_OWNER(pb)	((pb)->pb_last_holder = -1)
# define PB_GET_OWNER(pb)	((pb)->pb_last_holder)
#else
# define PB_SET_OWNER(pb)	do { } while (0)
# define PB_CLEAR_OWNER(pb)	do { } while (0)
# define PB_GET_OWNER(pb)	do { } while (0)
#endif

/*
 * Pagebuf allocation / freeing.
 */

#define pb_to_gfp(flags) \
	((((flags) & PBF_READ_AHEAD) ? __GFP_NORETRY : \
	  ((flags) & PBF_DONT_BLOCK) ? GFP_NOFS : GFP_KERNEL) | __GFP_NOWARN)

#define pb_to_km(flags) \
	 (((flags) & PBF_DONT_BLOCK) ? KM_NOFS : KM_SLEEP)


#define pagebuf_allocate(flags) \
	kmem_zone_alloc(pagebuf_zone, pb_to_km(flags))
#define pagebuf_deallocate(pb) \
	kmem_zone_free(pagebuf_zone, (pb));

/*
 * 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 inline void
set_page_region(
	struct page	*page,
	size_t		offset,
	size_t		length)
{
	page->private |= page_region_mask(offset, length);
	if (page->private == ~0UL)
		SetPageUptodate(page);
}

STATIC inline 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 & 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;

	aentry = kmalloc(sizeof(a_list_t), GFP_ATOMIC & ~__GFP_HIGH);
	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 pagebuf object manipulation
 */

STATIC void
_pagebuf_initialize(
	xfs_buf_t		*pb,
	xfs_buftarg_t		*target,
	loff_t			range_base,
	size_t			range_length,
	page_buf_flags_t	flags)
{
	/*
	 * We don't want certain flags to appear in pb->pb_flags.
	 */
	flags &= ~(PBF_LOCK|PBF_MAPPED|PBF_DONT_BLOCK|PBF_READ_AHEAD);

	memset(pb, 0, sizeof(xfs_buf_t));
	atomic_set(&pb->pb_hold, 1);
	init_MUTEX_LOCKED(&pb->pb_iodonesema);
	INIT_LIST_HEAD(&pb->pb_list);
	INIT_LIST_HEAD(&pb->pb_hash_list);
	init_MUTEX_LOCKED(&pb->pb_sema); /* held, no waiters */
	PB_SET_OWNER(pb);
	pb->pb_target = target;
	pb->pb_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).
	 */
	pb->pb_buffer_length = pb->pb_count_desired = range_length;
	pb->pb_flags = flags | PBF_NONE;
	pb->pb_bn = XFS_BUF_DADDR_NULL;
	atomic_set(&pb->pb_pin_count, 0);
	init_waitqueue_head(&pb->pb_waiters);

	XFS_STATS_INC(pb_create);
	PB_TRACE(pb, "initialize", target);
}

/*
 * Allocate a page array capable of holding a specified number
 * of pages, and point the page buf at it.
 */
STATIC int
_pagebuf_get_pages(
	xfs_buf_t		*pb,
	int			page_count,
	page_buf_flags_t	flags)
{
	/* Make sure that we have a page list */
	if (pb->pb_pages == NULL) {
		pb->pb_offset = page_buf_poff(pb->pb_file_offset);
		pb->pb_page_count = page_count;
		if (page_count <= PB_PAGES) {
			pb->pb_pages = pb->pb_page_array;
		} else {
			pb->pb_pages = kmem_alloc(sizeof(struct page *) *
					page_count, pb_to_km(flags));
			if (pb->pb_pages == NULL)
				return -ENOMEM;
		}
		memset(pb->pb_pages, 0, sizeof(struct page *) * page_count);
	}
	return 0;
}

/*
 *	Frees pb_pages if it was malloced.
 */
STATIC void
_pagebuf_free_pages(
	xfs_buf_t	*bp)
{
	if (bp->pb_pages != bp->pb_page_array) {
		kmem_free(bp->pb_pages,
			  bp->pb_page_count * sizeof(struct page *));
	}
}

/*
 *	Releases the specified buffer.
 *
 * 	The modification state of any associated pages is left unchanged.
 * 	The buffer most not be on any hash - use pagebuf_rele instead for
 * 	hashed and refcounted buffers
 */
void
pagebuf_free(
	xfs_buf_t		*bp)
{
	PB_TRACE(bp, "free", 0);

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

	if (bp->pb_flags & _PBF_PAGE_CACHE) {
		uint		i;

		if ((bp->pb_flags & PBF_MAPPED) && (bp->pb_page_count > 1))
			free_address(bp->pb_addr - bp->pb_offset);

		for (i = 0; i < bp->pb_page_count; i++)
			page_cache_release(bp->pb_pages[i]);
		_pagebuf_free_pages(bp);
	} else if (bp->pb_flags & _PBF_KMEM_ALLOC) {
		 /*
		  * XXX(hch): bp->pb_count_desired might be incorrect (see
		  * pagebuf_associate_memory for details), but fortunately
		  * the Linux version of kmem_free ignores the len argument..
		  */
		kmem_free(bp->pb_addr, bp->pb_count_desired);
		_pagebuf_free_pages(bp);
	}

	pagebuf_deallocate(bp);
}

/*
 *	Finds all pages for buffer in question and builds it's page list.
 */
STATIC int
_pagebuf_lookup_pages(
	xfs_buf_t		*bp,
	uint			flags)
{
	struct address_space	*mapping = bp->pb_target->pbr_mapping;
	size_t			blocksize = bp->pb_target->pbr_bsize;
	size_t			size = bp->pb_count_desired;
	size_t			nbytes, offset;
	gfp_t			gfp_mask = pb_to_gfp(flags);
	unsigned short		page_count, i;
	pgoff_t			first;
	loff_t			end;
	int			error;

	end = bp->pb_file_offset + bp->pb_buffer_length;
	page_count = page_buf_btoc(end) - page_buf_btoct(bp->pb_file_offset);

	error = _pagebuf_get_pages(bp, page_count, flags);
	if (unlikely(error))
		return error;
	bp->pb_flags |= _PBF_PAGE_CACHE;

	offset = bp->pb_offset;
	first = bp->pb_file_offset >> PAGE_CACHE_SHIFT;

	for (i = 0; i < bp->pb_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 & PBF_READ_AHEAD) {
				bp->pb_page_count = i;
				for (i = 0; i < bp->pb_page_count; i++)
					unlock_page(bp->pb_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",
					__FUNCTION__, gfp_mask);

			XFS_STATS_INC(pb_page_retries);
			xfsbufd_wakeup(0, gfp_mask);
			blk_congestion_wait(WRITE, HZ/50);
			goto retry;
		}

		XFS_STATS_INC(pb_page_found);

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

		if (!PageUptodate(page)) {
			page_count--;
			if (blocksize >= PAGE_CACHE_SIZE) {
				if (flags & PBF_READ)
					bp->pb_locked = 1;
			} else if (!PagePrivate(page)) {
				if (test_page_region(page, offset, nbytes))
					page_count++;
			}
		}

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

	if (!bp->pb_locked) {
		for (i = 0; i < bp->pb_page_count; i++)
			unlock_page(bp->pb_pages[i]);
	}

	if (page_count) {
		/* if we have any uptodate pages, mark that in the buffer */
		bp->pb_flags &= ~PBF_NONE;

		/* if some pages aren't uptodate, mark that in the buffer */
		if (page_count != bp->pb_page_count)
			bp->pb_flags |= PBF_PARTIAL;
	}

	PB_TRACE(bp, "lookup_pages", (long)page_count);
	return error;
}

/*
 *	Map buffer into kernel address-space if nessecary.
 */
STATIC int
_pagebuf_map_pages(
	xfs_buf_t		*bp,
	uint			flags)
{
	/* A single page buffer is always mappable */
	if (bp->pb_page_count == 1) {
		bp->pb_addr = page_address(bp->pb_pages[0]) + bp->pb_offset;
		bp->pb_flags |= PBF_MAPPED;
	} else if (flags & PBF_MAPPED) {
		if (as_list_len > 64)
			purge_addresses();
		bp->pb_addr = vmap(bp->pb_pages, bp->pb_page_count,
				VM_MAP, PAGE_KERNEL);
		if (unlikely(bp->pb_addr == NULL))
			return -ENOMEM;
		bp->pb_addr += bp->pb_offset;
		bp->pb_flags |= PBF_MAPPED;
	}

	return 0;
}

/*
 *	Finding and Reading Buffers
 */

/*
 *	_pagebuf_find
 *
 *	Looks 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 *
_pagebuf_find(
	xfs_buftarg_t		*btp,	/* block device target		*/
	loff_t			ioff,	/* starting offset of range	*/
	size_t			isize,	/* length of range		*/
	page_buf_flags_t	flags,	/* PBF_TRYLOCK			*/
	xfs_buf_t		*new_pb)/* newly allocated buffer	*/
{
	loff_t			range_base;
	size_t			range_length;
	xfs_bufhash_t		*hash;
	xfs_buf_t		*pb, *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->pbr_sshift)));
	ASSERT(!(range_base & (loff_t)btp->pbr_smask));

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

	spin_lock(&hash->bh_lock);

	list_for_each_entry_safe(pb, n, &hash->bh_list, pb_hash_list) {
		ASSERT(btp == pb->pb_target);
		if (pb->pb_file_offset == range_base &&
		    pb->pb_buffer_length == range_length) {
			/*
			 * If we look at something bring it to the
			 * front of the list for next time.
			 */
			atomic_inc(&pb->pb_hold);
			list_move(&pb->pb_hash_list, &hash->bh_list);
			goto found;
		}
	}

	/* No match found */
	if (new_pb) {
		_pagebuf_initialize(new_pb, btp, range_base,
				range_length, flags);
		new_pb->pb_hash = hash;
		list_add(&new_pb->pb_hash_list, &hash->bh_list);
	} else {
		XFS_STATS_INC(pb_miss_locked);
	}

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

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(&pb->pb_sema)) {
		if (!(flags & PBF_TRYLOCK)) {
			/* wait for buffer ownership */
			PB_TRACE(pb, "get_lock", 0);
			pagebuf_lock(pb);
			XFS_STATS_INC(pb_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 pagebuf at least overlaps our
			 * pagebuf and is locked, therefore our buffer
			 * either does not exist, or is this buffer
			 */

			pagebuf_rele(pb);
			XFS_STATS_INC(pb_busy_locked);
			return (NULL);
		}
	} else {
		/* trylock worked */
		PB_SET_OWNER(pb);
	}

	if (pb->pb_flags & PBF_STALE) {
		ASSERT((pb->pb_flags & _PBF_DELWRI_Q) == 0);
		pb->pb_flags &= PBF_MAPPED;
	}
	PB_TRACE(pb, "got_lock", 0);
	XFS_STATS_INC(pb_get_locked);
	return (pb);
}

/*
 *	xfs_buf_get_flags 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_flags(			/* allocate a buffer		*/
	xfs_buftarg_t		*target,/* target for buffer		*/
	loff_t			ioff,	/* starting offset of range	*/
	size_t			isize,	/* length of range		*/
	page_buf_flags_t	flags)	/* PBF_TRYLOCK			*/
{
	xfs_buf_t		*pb, *new_pb;
	int			error = 0, i;

	new_pb = pagebuf_allocate(flags);
	if (unlikely(!new_pb))
		return NULL;

	pb = _pagebuf_find(target, ioff, isize, flags, new_pb);
	if (pb == new_pb) {
		error = _pagebuf_lookup_pages(pb, flags);
		if (error)
			goto no_buffer;
	} else {
		pagebuf_deallocate(new_pb);
		if (unlikely(pb == NULL))
			return NULL;
	}

	for (i = 0; i < pb->pb_page_count; i++)
		mark_page_accessed(pb->pb_pages[i]);

	if (!(pb->pb_flags & PBF_MAPPED)) {
		error = _pagebuf_map_pages(pb, flags);
		if (unlikely(error)) {
			printk(KERN_WARNING "%s: failed to map pages\n",
					__FUNCTION__);
			goto no_buffer;
		}
	}

	XFS_STATS_INC(pb_get);

	/*
	 * Always fill in the block number now, the mapped cases can do
	 * their own overlay of this later.
	 */
	pb->pb_bn = ioff;
	pb->pb_count_desired = pb->pb_buffer_length;

	PB_TRACE(pb, "get", (unsigned long)flags);
	return pb;

 no_buffer:
	if (flags & (PBF_LOCK | PBF_TRYLOCK))
		pagebuf_unlock(pb);
	pagebuf_rele(pb);
	return NULL;
}

xfs_buf_t *
xfs_buf_read_flags(
	xfs_buftarg_t		*target,
	loff_t			ioff,
	size_t			isize,
	page_buf_flags_t	flags)
{
	xfs_buf_t		*pb;

	flags |= PBF_READ;

	pb = xfs_buf_get_flags(target, ioff, isize, flags);
	if (pb) {
		if (PBF_NOT_DONE(pb)) {
			PB_TRACE(pb, "read", (unsigned long)flags);
			XFS_STATS_INC(pb_get_read);
			pagebuf_iostart(pb, flags);
		} else if (flags & PBF_ASYNC) {
			PB_TRACE(pb, "read_async", (unsigned long)flags);
			/*
			 * Read ahead call which is already satisfied,
			 * drop the buffer
			 */
			goto no_buffer;
		} else {
			PB_TRACE(pb, "read_done", (unsigned long)flags);
			/* We do not want read in the flags */
			pb->pb_flags &= ~PBF_READ;
		}
	}

	return pb;

 no_buffer:
	if (flags & (PBF_LOCK | PBF_TRYLOCK))
		pagebuf_unlock(pb);
	pagebuf_rele(pb);
	return NULL;
}

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

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

	flags |= (PBF_TRYLOCK|PBF_ASYNC|PBF_READ_AHEAD);
	xfs_buf_read_flags(target, ioff, isize, flags);
}

xfs_buf_t *
pagebuf_get_empty(
	size_t			len,
	xfs_buftarg_t		*target)
{
	xfs_buf_t		*pb;

	pb = pagebuf_allocate(0);
	if (pb)
		_pagebuf_initialize(pb, target, 0, len, 0);
	return pb;
}

static inline struct page *
mem_to_page(
	void			*addr)
{
	if (((unsigned long)addr < VMALLOC_START) ||
	    ((unsigned long)addr >= VMALLOC_END)) {
		return virt_to_page(addr);
	} else {
		return vmalloc_to_page(addr);
	}
}

int
pagebuf_associate_memory(
	xfs_buf_t		*pb,
	void			*mem,
	size_t			len)
{
	int			rval;
	int			i = 0;
	size_t			ptr;
	size_t			end, end_cur;
	off_t			offset;
	int			page_count;

	page_count = PAGE_CACHE_ALIGN(len) >> PAGE_CACHE_SHIFT;
	offset = (off_t) mem - ((off_t)mem & PAGE_CACHE_MASK);
	if (offset && (len > PAGE_CACHE_SIZE))
		page_count++;

	/* Free any previous set of page pointers */
	if (pb->pb_pages)
		_pagebuf_free_pages(pb);

	pb->pb_pages = NULL;
	pb->pb_addr = mem;

	rval = _pagebuf_get_pages(pb, page_count, 0);
	if (rval)
		return rval;

	pb->pb_offset = offset;
	ptr = (size_t) mem & PAGE_CACHE_MASK;
	end = PAGE_CACHE_ALIGN((size_t) mem + len);
	end_cur = end;
	/* set up first page */
	pb->pb_pages[0] = mem_to_page(mem);

	ptr += PAGE_CACHE_SIZE;
	pb->pb_page_count = ++i;
	while (ptr < end) {
		pb->pb_pages[i] = mem_to_page((void *)ptr);
		pb->pb_page_count = ++i;
		ptr += PAGE_CACHE_SIZE;
	}
	pb->pb_locked = 0;

	pb->pb_count_desired = pb->pb_buffer_length = len;
	pb->pb_flags |= PBF_MAPPED;

	return 0;
}

xfs_buf_t *
pagebuf_get_no_daddr(
	size_t			len,
	xfs_buftarg_t		*target)
{
	size_t			malloc_len = len;
	xfs_buf_t		*bp;
	void			*data;
	int			error;

	bp = pagebuf_allocate(0);
	if (unlikely(bp == NULL))
		goto fail;
	_pagebuf_initialize(bp, target, 0, len, PBF_FORCEIO);

 try_again:
	data = kmem_alloc(malloc_len, KM_SLEEP | KM_MAYFAIL);
	if (unlikely(data == NULL))
		goto fail_free_buf;

	/* check whether alignment matches.. */
	if ((__psunsigned_t)data !=
	    ((__psunsigned_t)data & ~target->pbr_smask)) {
		/* .. else double the size and try again */
		kmem_free(data, malloc_len);
		malloc_len <<= 1;
		goto try_again;
	}

	error = pagebuf_associate_memory(bp, data, len);
	if (error)
		goto fail_free_mem;
	bp->pb_flags |= _PBF_KMEM_ALLOC;

	pagebuf_unlock(bp);

	PB_TRACE(bp, "no_daddr", data);
	return bp;
 fail_free_mem:
	kmem_free(data, malloc_len);
 fail_free_buf:
	pagebuf_free(bp);
 fail:
	return NULL;
}

/*
 *	pagebuf_hold
 *
 *	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
pagebuf_hold(
	xfs_buf_t		*pb)
{
	atomic_inc(&pb->pb_hold);
	PB_TRACE(pb, "hold", 0);
}

/*
 *	pagebuf_rele
 *
 *	pagebuf_rele releases a hold on the specified buffer.  If the
 *	the hold count is 1, pagebuf_rele calls pagebuf_free.
 */
void
pagebuf_rele(
	xfs_buf_t		*pb)
{
	xfs_bufhash_t		*hash = pb->pb_hash;

	PB_TRACE(pb, "rele", pb->pb_relse);

	/*
	 * pagebuf_lookup buffers are not hashed, not delayed write,
	 * and don't have their own release routines.  Special case.
	 */
	if (unlikely(!hash)) {
		ASSERT(!pb->pb_relse);
		if (atomic_dec_and_test(&pb->pb_hold))
			xfs_buf_free(pb);
		return;
	}

	if (atomic_dec_and_lock(&pb->pb_hold, &hash->bh_lock)) {
		int		do_free = 1;

		if (pb->pb_relse) {
			atomic_inc(&pb->pb_hold);
			spin_unlock(&hash->bh_lock);
			(*(pb->pb_relse)) (pb);
			spin_lock(&hash->bh_lock);
			do_free = 0;
		}

		if (pb->pb_flags & PBF_FS_MANAGED) {
			do_free = 0;
		}

		if (do_free) {
			ASSERT((pb->pb_flags & (PBF_DELWRI|_PBF_DELWRI_Q)) == 0);
			list_del_init(&pb->pb_hash_list);
			spin_unlock(&hash->bh_lock);
			pagebuf_free(pb);
		} else {
			spin_unlock(&hash->bh_lock);
		}
	} else {
		/*
		 * Catch reference count leaks
		 */
		ASSERT(atomic_read(&pb->pb_hold) >= 0);
	}
}


/*
 *	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.
 */

/*
 *	pagebuf_cond_lock
 *
 *	pagebuf_cond_lock 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 page buffer objects, not for synchronizing independent
 *	access to the underlying pages.
 */
int
pagebuf_cond_lock(			/* lock buffer, if not locked	*/
					/* returns -EBUSY if locked)	*/
	xfs_buf_t		*pb)
{
	int			locked;

	locked = down_trylock(&pb->pb_sema) == 0;
	if (locked) {
		PB_SET_OWNER(pb);
	}
	PB_TRACE(pb, "cond_lock", (long)locked);
	return(locked ? 0 : -EBUSY);
}

#if defined(DEBUG) || defined(XFS_BLI_TRACE)
/*
 *	pagebuf_lock_value
 *
 *	Return lock value for a pagebuf
 */
int
pagebuf_lock_value(
	xfs_buf_t		*pb)
{
	return(atomic_read(&pb->pb_sema.count));
}
#endif

/*
 *	pagebuf_lock
 *
 *	pagebuf_lock locks a buffer object.  Note that this in no way
 *	locks the underlying pages, so it is only useful for synchronizing
 *	concurrent use of page buffer objects, not for synchronizing independent
 *	access to the underlying pages.
 */
int
pagebuf_lock(
	xfs_buf_t		*pb)
{
	PB_TRACE(pb, "lock", 0);
	if (atomic_read(&pb->pb_io_remaining))
		blk_run_address_space(pb->pb_target->pbr_mapping);
	down(&pb->pb_sema);
	PB_SET_OWNER(pb);
	PB_TRACE(pb, "locked", 0);
	return 0;
}

/*
 *	pagebuf_unlock
 *
 *	pagebuf_unlock releases the lock on the buffer object created by
 *	pagebuf_lock or pagebuf_cond_lock (not any pinning of underlying pages
 *	created by pagebuf_pin).
 *
 *	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
pagebuf_unlock(				/* unlock buffer		*/
	xfs_buf_t		*pb)	/* buffer to unlock		*/
{
	if ((pb->pb_flags & (PBF_DELWRI|_PBF_DELWRI_Q)) == PBF_DELWRI) {
		atomic_inc(&pb->pb_hold);
		pb->pb_flags |= PBF_ASYNC;
		pagebuf_delwri_queue(pb, 0);
	}

	PB_CLEAR_OWNER(pb);
	up(&pb->pb_sema);
	PB_TRACE(pb, "unlock", 0);
}


/*
 *	Pinning Buffer Storage in Memory
 */

/*
 *	pagebuf_pin
 *
 *	pagebuf_pin locks all of the memory represented by a buffer in
 *	memory.  Multiple calls to pagebuf_pin and pagebuf_unpin, for
 *	the same or different buffers affecting a given page, will
 *	properly count the number of outstanding "pin" requests.  The
 *	buffer may be released after the pagebuf_pin and a different
 *	buffer used when calling pagebuf_unpin, if desired.
 *	pagebuf_pin should be used by the file system when it wants be
 *	assured that no attempt will be made to force the affected
 *	memory to disk.	 It does not assure that a given logical page
 *	will not be moved to a different physical page.
 */
void
pagebuf_pin(
	xfs_buf_t		*pb)
{
	atomic_inc(&pb->pb_pin_count);
	PB_TRACE(pb, "pin", (long)pb->pb_pin_count.counter);
}

/*
 *	pagebuf_unpin
 *
 *	pagebuf_unpin reverses the locking of memory performed by
 *	pagebuf_pin.  Note that both functions affected the logical
 *	pages associated with the buffer, not the buffer itself.
 */
void
pagebuf_unpin(
	xfs_buf_t		*pb)
{
	if (atomic_dec_and_test(&pb->pb_pin_count)) {
		wake_up_all(&pb->pb_waiters);
	}
	PB_TRACE(pb, "unpin", (long)pb->pb_pin_count.counter);
}

int
pagebuf_ispin(
	xfs_buf_t		*pb)
{
	return atomic_read(&pb->pb_pin_count);
}

/*
 *	pagebuf_wait_unpin
 *
 *	pagebuf_wait_unpin waits until all of the memory associated
 *	with the buffer is not longer locked in memory.  It returns
 *	immediately if none of the affected pages are locked.
 */
static inline void
_pagebuf_wait_unpin(
	xfs_buf_t		*pb)
{
	DECLARE_WAITQUEUE	(wait, current);

	if (atomic_read(&pb->pb_pin_count) == 0)
		return;

	add_wait_queue(&pb->pb_waiters, &wait);
	for (;;) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (atomic_read(&pb->pb_pin_count) == 0)
			break;
		if (atomic_read(&pb->pb_io_remaining))
			blk_run_address_space(pb->pb_target->pbr_mapping);
		schedule();
	}
	remove_wait_queue(&pb->pb_waiters, &wait);
	set_current_state(TASK_RUNNING);
}

/*
 *	Buffer Utility Routines
 */

/*
 *	pagebuf_iodone
 *
 *	pagebuf_iodone marks a buffer for which I/O is in progress
 *	done with respect to that I/O.	The pb_iodone routine, if
 *	present, will be called as a side-effect.
 */
STATIC void
pagebuf_iodone_work(
	void			*v)
{
	xfs_buf_t		*bp = (xfs_buf_t *)v;

	if (bp->pb_iodone)
		(*(bp->pb_iodone))(bp);
	else if (bp->pb_flags & PBF_ASYNC)
		xfs_buf_relse(bp);
}

void
pagebuf_iodone(
	xfs_buf_t		*pb,
	int			dataio,
	int			schedule)
{
	pb->pb_flags &= ~(PBF_READ | PBF_WRITE);
	if (pb->pb_error == 0) {
		pb->pb_flags &= ~(PBF_PARTIAL | PBF_NONE);
	}

	PB_TRACE(pb, "iodone", pb->pb_iodone);

	if ((pb->pb_iodone) || (pb->pb_flags & PBF_ASYNC)) {
		if (schedule) {
			INIT_WORK(&pb->pb_iodone_work, pagebuf_iodone_work, pb);
			queue_work(dataio ? xfsdatad_workqueue :
				xfslogd_workqueue, &pb->pb_iodone_work);
		} else {
			pagebuf_iodone_work(pb);
		}
	} else {
		up(&pb->pb_iodonesema);
	}
}

/*
 *	pagebuf_ioerror
 *
 *	pagebuf_ioerror sets the error code for a buffer.
 */
void
pagebuf_ioerror(			/* mark/clear buffer error flag */
	xfs_buf_t		*pb,	/* buffer to mark		*/
	int			error)	/* error to store (0 if none)	*/
{
	ASSERT(error >= 0 && error <= 0xffff);
	pb->pb_error = (unsigned short)error;
	PB_TRACE(pb, "ioerror", (unsigned long)error);
}

/*
 *	pagebuf_iostart
 *
 *	pagebuf_iostart initiates I/O on a buffer, based on the flags supplied.
 *	If necessary, it will arrange for any disk space allocation required,
 *	and it will break up the request if the block mappings require it.
 *	The pb_iodone routine in the buffer supplied will only be called
 *	when all of the subsidiary I/O requests, if any, have been completed.
 *	pagebuf_iostart calls the pagebuf_ioinitiate routine or
 *	pagebuf_iorequest, if the former routine is not defined, to start
 *	the I/O on a given low-level request.
 */
int
pagebuf_iostart(			/* start I/O on a buffer	  */
	xfs_buf_t		*pb,	/* buffer to start		  */
	page_buf_flags_t	flags)	/* PBF_LOCK, PBF_ASYNC, PBF_READ, */
					/* PBF_WRITE, PBF_DELWRI,	  */
					/* PBF_DONT_BLOCK		  */
{
	int			status = 0;

	PB_TRACE(pb, "iostart", (unsigned long)flags);

	if (flags & PBF_DELWRI) {
		pb->pb_flags &= ~(PBF_READ | PBF_WRITE | PBF_ASYNC);
		pb->pb_flags |= flags & (PBF_DELWRI | PBF_ASYNC);
		pagebuf_delwri_queue(pb, 1);
		return status;
	}

	pb->pb_flags &= ~(PBF_READ | PBF_WRITE | PBF_ASYNC | PBF_DELWRI | \
			PBF_READ_AHEAD | _PBF_RUN_QUEUES);
	pb->pb_flags |= flags & (PBF_READ | PBF_WRITE | PBF_ASYNC | \
			PBF_READ_AHEAD | _PBF_RUN_QUEUES);

	BUG_ON(pb->pb_bn == XFS_BUF_DADDR_NULL);

	/* For writes allow an alternate strategy routine to precede
	 * the actual I/O request (which may not be issued at all in
	 * a shutdown situation, for example).
	 */
	status = (flags & PBF_WRITE) ?
		pagebuf_iostrategy(pb) : pagebuf_iorequest(pb);

	/* Wait for I/O if we are not an async request.
	 * Note: async I/O request completion will release the buffer,
	 * and that can already be done by this point.  So using the
	 * buffer pointer from here on, after async I/O, is invalid.
	 */
	if (!status && !(flags & PBF_ASYNC))
		status = pagebuf_iowait(pb);

	return status;
}

/*
 * Helper routine for pagebuf_iorequest
 */

STATIC __inline__ int
_pagebuf_iolocked(
	xfs_buf_t		*pb)
{
	ASSERT(pb->pb_flags & (PBF_READ|PBF_WRITE));
	if (pb->pb_flags & PBF_READ)
		return pb->pb_locked;
	return 0;
}

STATIC __inline__ void
_pagebuf_iodone(
	xfs_buf_t		*pb,
	int			schedule)
{
	if (atomic_dec_and_test(&pb->pb_io_remaining) == 1) {
		pb->pb_locked = 0;
		pagebuf_iodone(pb, (pb->pb_flags & PBF_FS_DATAIOD), schedule);
	}
}

STATIC int
bio_end_io_pagebuf(
	struct bio		*bio,
	unsigned int		bytes_done,
	int			error)
{
	xfs_buf_t		*pb = (xfs_buf_t *)bio->bi_private;
	unsigned int		blocksize = pb->pb_target->pbr_bsize;
	struct bio_vec		*bvec = bio->bi_io_vec + bio->bi_vcnt - 1;

	if (bio->bi_size)
		return 1;

	if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
		pb->pb_error = EIO;

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

		if (unlikely(pb->pb_error)) {
			if (pb->pb_flags & PBF_READ)
				ClearPageUptodate(page);
			SetPageError(page);
		} else if (blocksize == PAGE_CACHE_SIZE) {
			SetPageUptodate(page);
		} else if (!PagePrivate(page) &&
				(pb->pb_flags & _PBF_PAGE_CACHE)) {
			set_page_region(page, bvec->bv_offset, bvec->bv_len);
		}

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

		if (_pagebuf_iolocked(pb)) {
			unlock_page(page);
		}
	} while (bvec >= bio->bi_io_vec);

	_pagebuf_iodone(pb, 1);
	bio_put(bio);
	return 0;
}

STATIC void
_pagebuf_ioapply(
	xfs_buf_t		*pb)
{
	int			i, rw, map_i, total_nr_pages, nr_pages;
	struct bio		*bio;
	int			offset = pb->pb_offset;
	int			size = pb->pb_count_desired;
	sector_t		sector = pb->pb_bn;
	unsigned int		blocksize = pb->pb_target->pbr_bsize;
	int			locking = _pagebuf_iolocked(pb);

	total_nr_pages = pb->pb_page_count;
	map_i = 0;

	if (pb->pb_flags & _PBF_RUN_QUEUES) {
		pb->pb_flags &= ~_PBF_RUN_QUEUES;
		rw = (pb->pb_flags & PBF_READ) ? READ_SYNC : WRITE_SYNC;
	} else {
		rw = (pb->pb_flags & PBF_READ) ? READ : WRITE;
	}

	/* Special code path for reading a sub page size pagebuf 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 and the page size are equal.
	 */
	if ((pb->pb_buffer_length < PAGE_CACHE_SIZE) &&
	    (pb->pb_flags & PBF_READ) && locking &&
	    (blocksize == PAGE_CACHE_SIZE)) {
		bio = bio_alloc(GFP_NOIO, 1);

		bio->bi_bdev = pb->pb_target->pbr_bdev;
		bio->bi_sector = sector - (offset >> BBSHIFT);
		bio->bi_end_io = bio_end_io_pagebuf;
		bio->bi_private = pb;

		bio_add_page(bio, pb->pb_pages[0], PAGE_CACHE_SIZE, 0);
		size = 0;

		atomic_inc(&pb->pb_io_remaining);

		goto submit_io;
	}

	/* Lock down the pages which we need to for the request */
	if (locking && (pb->pb_flags & PBF_WRITE) && (pb->pb_locked == 0)) {
		for (i = 0; size; i++) {
			int		nbytes = PAGE_CACHE_SIZE - offset;
			struct page	*page = pb->pb_pages[i];

			if (nbytes > size)
				nbytes = size;

			lock_page(page);

			size -= nbytes;
			offset = 0;
		}
		offset = pb->pb_offset;
		size = pb->pb_count_desired;
	}

next_chunk:
	atomic_inc(&pb->pb_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 = pb->pb_target->pbr_bdev;
	bio->bi_sector = sector;
	bio->bi_end_io = bio_end_io_pagebuf;
	bio->bi_private = pb;

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

		if (nbytes > size)
			nbytes = size;

		if (bio_add_page(bio, pb->pb_pages[map_i],
					nbytes, offset) < 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);
		pagebuf_ioerror(pb, EIO);
	}
}

/*
 *	pagebuf_iorequest -- the core I/O request routine.
 */
int
pagebuf_iorequest(			/* start real I/O		*/
	xfs_buf_t		*pb)	/* buffer to convey to device	*/
{
	PB_TRACE(pb, "iorequest", 0);

	if (pb->pb_flags & PBF_DELWRI) {
		pagebuf_delwri_queue(pb, 1);
		return 0;
	}

	if (pb->pb_flags & PBF_WRITE) {
		_pagebuf_wait_unpin(pb);
	}

	pagebuf_hold(pb);

	/* 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 pagebuf_iodone too early.
	 */
	atomic_set(&pb->pb_io_remaining, 1);
	_pagebuf_ioapply(pb);
	_pagebuf_iodone(pb, 0);

	pagebuf_rele(pb);
	return 0;
}

/*
 *	pagebuf_iowait
 *
 *	pagebuf_iowait waits for I/O to complete on the buffer supplied.
 *	It returns immediately if no I/O is pending.  In any case, it returns
 *	the error code, if any, or 0 if there is no error.
 */
int
pagebuf_iowait(
	xfs_buf_t		*pb)
{
	PB_TRACE(pb, "iowait", 0);
	if (atomic_read(&pb->pb_io_remaining))
		blk_run_address_space(pb->pb_target->pbr_mapping);
	down(&pb->pb_iodonesema);
	PB_TRACE(pb, "iowaited", (long)pb->pb_error);
	return pb->pb_error;
}

caddr_t
pagebuf_offset(
	xfs_buf_t		*pb,
	size_t			offset)
{
	struct page		*page;

	offset += pb->pb_offset;

	page = pb->pb_pages[offset >> PAGE_CACHE_SHIFT];
	return (caddr_t) page_address(page) + (offset & (PAGE_CACHE_SIZE - 1));
}

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

	bend = boff + bsize;
	while (boff < bend) {
		page = pb->pb_pages[page_buf_btoct(boff + pb->pb_offset)];
		cpoff = page_buf_poff(boff + pb->pb_offset);
		csize = min_t(size_t,
			      PAGE_CACHE_SIZE-cpoff, pb->pb_count_desired-boff);

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

		switch (mode) {
		case PBRW_ZERO:
			memset(page_address(page) + cpoff, 0, csize);
			break;
		case PBRW_READ:
			memcpy(data, page_address(page) + cpoff, csize);
			break;
		case PBRW_WRITE:
			memcpy(page_address(page) + cpoff, data, csize);
		}

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

/*
 *	Handling of 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, pb_hash_list) {
			ASSERT(btp == bp->pb_target);
			if (!(bp->pb_flags & PBF_FS_MANAGED)) {
				spin_unlock(&hash->bh_lock);
				/*
				 * Catch superblock reference count leaks
				 * immediately
				 */
				BUG_ON(bp->pb_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);
	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,
			(1 << btp->bt_hashshift) * sizeof(xfs_bufhash_t));
	btp->bt_hash = NULL;
}

void
xfs_free_buftarg(
	xfs_buftarg_t		*btp,
	int			external)
{
	xfs_flush_buftarg(btp, 1);
	if (external)
		xfs_blkdev_put(btp->pbr_bdev);
	xfs_free_bufhash(btp);
	iput(btp->pbr_mapping->host);
	kmem_free(btp, sizeof(*btp));
}

STATIC int
xfs_setsize_buftarg_flags(
	xfs_buftarg_t		*btp,
	unsigned int		blocksize,
	unsigned int		sectorsize,
	int			verbose)
{
	btp->pbr_bsize = blocksize;
	btp->pbr_sshift = ffs(sectorsize) - 1;
	btp->pbr_smask = sectorsize - 1;

	if (set_blocksize(btp->pbr_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_hardsect_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 struct address_space_operations mapping_aops = {
		.sync_page = block_sync_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->pbr_mapping = mapping;
	return 0;
}

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

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

	btp->pbr_dev =  bdev->bd_dev;
	btp->pbr_bdev = bdev;
	if (xfs_setsize_buftarg_early(btp, bdev))
		goto error;
	if (xfs_mapping_buftarg(btp, bdev))
		goto error;
	xfs_alloc_bufhash(btp, external);
	return btp;

error:
	kmem_free(btp, sizeof(*btp));
	return NULL;
}


/*
 * Pagebuf delayed write buffer handling
 */

STATIC LIST_HEAD(pbd_delwrite_queue);
STATIC DEFINE_SPINLOCK(pbd_delwrite_lock);

STATIC void
pagebuf_delwri_queue(
	xfs_buf_t		*pb,
	int			unlock)
{
	PB_TRACE(pb, "delwri_q", (long)unlock);
	ASSERT((pb->pb_flags & (PBF_DELWRI|PBF_ASYNC)) ==
					(PBF_DELWRI|PBF_ASYNC));

	spin_lock(&pbd_delwrite_lock);
	/* If already in the queue, dequeue and place at tail */
	if (!list_empty(&pb->pb_list)) {
		ASSERT(pb->pb_flags & _PBF_DELWRI_Q);
		if (unlock) {
			atomic_dec(&pb->pb_hold);
		}
		list_del(&pb->pb_list);
	}

	pb->pb_flags |= _PBF_DELWRI_Q;
	list_add_tail(&pb->pb_list, &pbd_delwrite_queue);
	pb->pb_queuetime = jiffies;
	spin_unlock(&pbd_delwrite_lock);

	if (unlock)
		pagebuf_unlock(pb);
}

void
pagebuf_delwri_dequeue(
	xfs_buf_t		*pb)
{
	int			dequeued = 0;

	spin_lock(&pbd_delwrite_lock);
	if ((pb->pb_flags & PBF_DELWRI) && !list_empty(&pb->pb_list)) {
		ASSERT(pb->pb_flags & _PBF_DELWRI_Q);
		list_del_init(&pb->pb_list);
		dequeued = 1;
	}
	pb->pb_flags &= ~(PBF_DELWRI|_PBF_DELWRI_Q);
	spin_unlock(&pbd_delwrite_lock);

	if (dequeued)
		pagebuf_rele(pb);

	PB_TRACE(pb, "delwri_dq", (long)dequeued);
}

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

/* Defines for pagebuf daemon */
STATIC struct task_struct *xfsbufd_task;
STATIC int xfsbufd_force_flush;
STATIC int xfsbufd_force_sleep;

STATIC int
xfsbufd_wakeup(
	int		priority,
	gfp_t		mask)
{
	if (xfsbufd_force_sleep)
		return 0;
	xfsbufd_force_flush = 1;
	barrier();
	wake_up_process(xfsbufd_task);
	return 0;
}

STATIC int
xfsbufd(
	void			*data)
{
	struct list_head	tmp;
	unsigned long		age;
	xfs_buftarg_t		*target;
	xfs_buf_t		*pb, *n;

	current->flags |= PF_MEMALLOC;

	INIT_LIST_HEAD(&tmp);
	do {
		if (unlikely(freezing(current))) {
			xfsbufd_force_sleep = 1;
			refrigerator();
		} else {
			xfsbufd_force_sleep = 0;
		}

		schedule_timeout_interruptible
			(xfs_buf_timer_centisecs * msecs_to_jiffies(10));

		age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
		spin_lock(&pbd_delwrite_lock);
		list_for_each_entry_safe(pb, n, &pbd_delwrite_queue, pb_list) {
			PB_TRACE(pb, "walkq1", (long)pagebuf_ispin(pb));
			ASSERT(pb->pb_flags & PBF_DELWRI);

			if (!pagebuf_ispin(pb) && !pagebuf_cond_lock(pb)) {
				if (!xfsbufd_force_flush &&
				    time_before(jiffies,
						pb->pb_queuetime + age)) {
					pagebuf_unlock(pb);
					break;
				}

				pb->pb_flags &= ~(PBF_DELWRI|_PBF_DELWRI_Q);
				pb->pb_flags |= PBF_WRITE;
				list_move(&pb->pb_list, &tmp);
			}
		}
		spin_unlock(&pbd_delwrite_lock);

		while (!list_empty(&tmp)) {
			pb = list_entry(tmp.next, xfs_buf_t, pb_list);
			target = pb->pb_target;

			list_del_init(&pb->pb_list);
			pagebuf_iostrategy(pb);

			blk_run_address_space(target->pbr_mapping);
		}

		if (as_list_len > 0)
			purge_addresses();

		xfsbufd_force_flush = 0;
	} 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		*pb, *n;
	int			pincount = 0;

	pagebuf_runall_queues(xfsdatad_workqueue);
	pagebuf_runall_queues(xfslogd_workqueue);

	INIT_LIST_HEAD(&tmp);
	spin_lock(&pbd_delwrite_lock);
	list_for_each_entry_safe(pb, n, &pbd_delwrite_queue, pb_list) {

		if (pb->pb_target != target)
			continue;

		ASSERT(pb->pb_flags & (PBF_DELWRI|_PBF_DELWRI_Q));
		PB_TRACE(pb, "walkq2", (long)pagebuf_ispin(pb));
		if (pagebuf_ispin(pb)) {
			pincount++;
			continue;
		}

		list_move(&pb->pb_list, &tmp);
	}
	spin_unlock(&pbd_delwrite_lock);

	/*
	 * Dropped the delayed write list lock, now walk the temporary list
	 */
	list_for_each_entry_safe(pb, n, &tmp, pb_list) {
		pagebuf_lock(pb);
		pb->pb_flags &= ~(PBF_DELWRI|_PBF_DELWRI_Q);
		pb->pb_flags |= PBF_WRITE;
		if (wait)
			pb->pb_flags &= ~PBF_ASYNC;
		else
			list_del_init(&pb->pb_list);

		pagebuf_iostrategy(pb);
	}

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

		list_del_init(&pb->pb_list);
		xfs_iowait(pb);
		xfs_buf_relse(pb);
	}

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

	return pincount;
}

STATIC int
xfs_buf_daemons_start(void)
{
	int		error = -ENOMEM;

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

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

	xfsbufd_task = kthread_run(xfsbufd, NULL, "xfsbufd");
	if (IS_ERR(xfsbufd_task)) {
		error = PTR_ERR(xfsbufd_task);
		goto out_destroy_xfsdatad_workqueue;
	}
	return 0;

 out_destroy_xfsdatad_workqueue:
	destroy_workqueue(xfsdatad_workqueue);
 out_destroy_xfslogd_workqueue:
	destroy_workqueue(xfslogd_workqueue);
 out:
	return error;
}

/*
 * Note: do not mark as __exit, it is called from pagebuf_terminate.
 */
STATIC void
xfs_buf_daemons_stop(void)
{
	kthread_stop(xfsbufd_task);
	destroy_workqueue(xfslogd_workqueue);
	destroy_workqueue(xfsdatad_workqueue);
}

/*
 *	Initialization and Termination
 */

int __init
pagebuf_init(void)
{
	int		error = -ENOMEM;

	pagebuf_zone = kmem_zone_init(sizeof(xfs_buf_t), "xfs_buf");
	if (!pagebuf_zone)
		goto out;

#ifdef PAGEBUF_TRACE
	pagebuf_trace_buf = ktrace_alloc(PAGEBUF_TRACE_SIZE, KM_SLEEP);
#endif

	error = xfs_buf_daemons_start();
	if (error)
		goto out_free_buf_zone;

	pagebuf_shake = kmem_shake_register(xfsbufd_wakeup);
	if (!pagebuf_shake) {
		error = -ENOMEM;
		goto out_stop_daemons;
	}

	return 0;

 out_stop_daemons:
	xfs_buf_daemons_stop();
 out_free_buf_zone:
#ifdef PAGEBUF_TRACE
	ktrace_free(pagebuf_trace_buf);
#endif
	kmem_zone_destroy(pagebuf_zone);
 out:
	return error;
}


/*
 *	pagebuf_terminate.
 *
 *	Note: do not mark as __exit, this is also called from the __init code.
 */
void
pagebuf_terminate(void)
{
	xfs_buf_daemons_stop();

#ifdef PAGEBUF_TRACE
	ktrace_free(pagebuf_trace_buf);
#endif

	kmem_zone_destroy(pagebuf_zone);
	kmem_shake_deregister(pagebuf_shake);
}