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Use the right offset when ensuring a delayed allocate conversion has covered the offset originally requested.  Can cause data corruption when multiple processes are performing writeout on different areas of the same file.  Quite difficult to hit though.
Merge of xfs-linux-melb:xfs-kern:22377a by kenmcd.

/*
 * 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/
 */

#include "xfs.h"
#include "xfs_inum.h"
#include "xfs_log.h"
#include "xfs_sb.h"
#include "xfs_dir.h"
#include "xfs_dir2.h"
#include "xfs_trans.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_alloc.h"
#include "xfs_btree.h"
#include "xfs_attr_sf.h"
#include "xfs_dir_sf.h"
#include "xfs_dir2_sf.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_error.h"
#include "xfs_rw.h"
#include "xfs_iomap.h"
#include <linux/mpage.h>
#include <linux/writeback.h>

STATIC void xfs_count_page_state(struct page *, int *, int *, int *);
STATIC void xfs_convert_page(struct inode *, struct page *, xfs_iomap_t *,
		struct writeback_control *wbc, void *, int, int);

#if defined(XFS_RW_TRACE)
void
xfs_page_trace(
	int		tag,
	struct inode	*inode,
	struct page	*page,
	int		mask)
{
	xfs_inode_t	*ip;
	bhv_desc_t	*bdp;
	vnode_t		*vp = LINVFS_GET_VP(inode);
	loff_t		isize = i_size_read(inode);
	loff_t		offset = (loff_t)page->index << PAGE_CACHE_SHIFT;
	int		delalloc = -1, unmapped = -1, unwritten = -1;

	if (page_has_buffers(page))
		xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);

	bdp = vn_bhv_lookup(VN_BHV_HEAD(vp), &xfs_vnodeops);
	ip = XFS_BHVTOI(bdp);
	if (!ip->i_rwtrace)
		return;

	ktrace_enter(ip->i_rwtrace,
		(void *)((unsigned long)tag),
		(void *)ip,
		(void *)inode,
		(void *)page,
		(void *)((unsigned long)mask),
		(void *)((unsigned long)((ip->i_d.di_size >> 32) & 0xffffffff)),
		(void *)((unsigned long)(ip->i_d.di_size & 0xffffffff)),
		(void *)((unsigned long)((isize >> 32) & 0xffffffff)),
		(void *)((unsigned long)(isize & 0xffffffff)),
		(void *)((unsigned long)((offset >> 32) & 0xffffffff)),
		(void *)((unsigned long)(offset & 0xffffffff)),
		(void *)((unsigned long)delalloc),
		(void *)((unsigned long)unmapped),
		(void *)((unsigned long)unwritten),
		(void *)NULL,
		(void *)NULL);
}
#else
#define xfs_page_trace(tag, inode, page, mask)
#endif

void
linvfs_unwritten_done(
	struct buffer_head	*bh,
	int			uptodate)
{
	xfs_buf_t		*pb = (xfs_buf_t *)bh->b_private;

	ASSERT(buffer_unwritten(bh));
	bh->b_end_io = NULL;
	clear_buffer_unwritten(bh);
	if (!uptodate)
		pagebuf_ioerror(pb, EIO);
	if (atomic_dec_and_test(&pb->pb_io_remaining) == 1) {
		pagebuf_iodone(pb, 1, 1);
	}
	end_buffer_async_write(bh, uptodate);
}

/*
 * Issue transactions to convert a buffer range from unwritten
 * to written extents (buffered IO).
 */
STATIC void
linvfs_unwritten_convert(
	xfs_buf_t	*bp)
{
	vnode_t		*vp = XFS_BUF_FSPRIVATE(bp, vnode_t *);
	int		error;

	BUG_ON(atomic_read(&bp->pb_hold) < 1);
	VOP_BMAP(vp, XFS_BUF_OFFSET(bp), XFS_BUF_SIZE(bp),
			BMAPI_UNWRITTEN, NULL, NULL, error);
	XFS_BUF_SET_FSPRIVATE(bp, NULL);
	XFS_BUF_CLR_IODONE_FUNC(bp);
	XFS_BUF_UNDATAIO(bp);
	iput(LINVFS_GET_IP(vp));
	pagebuf_iodone(bp, 0, 0);
}

/*
 * Issue transactions to convert a buffer range from unwritten
 * to written extents (direct IO).
 */
STATIC void
linvfs_unwritten_convert_direct(
	struct inode	*inode,
	loff_t		offset,
	ssize_t		size,
	void		*private)
{
	ASSERT(!private || inode == (struct inode *)private);

	/* private indicates an unwritten extent lay beneath this IO */
	if (private && size > 0) {
		vnode_t	*vp = LINVFS_GET_VP(inode);
		int	error;

		VOP_BMAP(vp, offset, size, BMAPI_UNWRITTEN, NULL, NULL, error);
	}
}

STATIC int
xfs_map_blocks(
	struct inode		*inode,
	loff_t			offset,
	ssize_t			count,
	xfs_iomap_t		*mapp,
	int			flags)
{
	vnode_t			*vp = LINVFS_GET_VP(inode);
	int			error, nmaps = 1;

	VOP_BMAP(vp, offset, count, flags, mapp, &nmaps, error);
	if (!error && (flags & (BMAPI_WRITE|BMAPI_ALLOCATE)))
		VMODIFY(vp);
	return -error;
}

/*
 * Finds the corresponding mapping in block @map array of the
 * given @offset within a @page.
 */
STATIC xfs_iomap_t *
xfs_offset_to_map(
	struct page		*page,
	xfs_iomap_t		*iomapp,
	unsigned long		offset)
{
	loff_t			full_offset;	/* offset from start of file */

	ASSERT(offset < PAGE_CACHE_SIZE);

	full_offset = page->index;		/* NB: using 64bit number */
	full_offset <<= PAGE_CACHE_SHIFT;	/* offset from file start */
	full_offset += offset;			/* offset from page start */

	if (full_offset < iomapp->iomap_offset)
		return NULL;
	if (iomapp->iomap_offset + (iomapp->iomap_bsize -1) >= full_offset)
		return iomapp;
	return NULL;
}

STATIC void
xfs_map_at_offset(
	struct page		*page,
	struct buffer_head	*bh,
	unsigned long		offset,
	int			block_bits,
	xfs_iomap_t		*iomapp)
{
	xfs_daddr_t		bn;
	loff_t			delta;
	int			sector_shift;

	ASSERT(!(iomapp->iomap_flags & IOMAP_HOLE));
	ASSERT(!(iomapp->iomap_flags & IOMAP_DELAY));
	ASSERT(iomapp->iomap_bn != IOMAP_DADDR_NULL);

	delta = page->index;
	delta <<= PAGE_CACHE_SHIFT;
	delta += offset;
	delta -= iomapp->iomap_offset;
	delta >>= block_bits;

	sector_shift = block_bits - BBSHIFT;
	bn = iomapp->iomap_bn >> sector_shift;
	bn += delta;
	BUG_ON(!bn && !(iomapp->iomap_flags & IOMAP_REALTIME));
	ASSERT((bn << sector_shift) >= iomapp->iomap_bn);

	lock_buffer(bh);
	bh->b_blocknr = bn;
	bh->b_bdev = iomapp->iomap_target->pbr_bdev;
	set_buffer_mapped(bh);
	clear_buffer_delay(bh);
}

/*
 * Look for a page at index which is unlocked and contains our
 * unwritten extent flagged buffers at its head.  Returns page
 * locked and with an extra reference count, and length of the
 * unwritten extent component on this page that we can write,
 * in units of filesystem blocks.
 */
STATIC struct page *
xfs_probe_unwritten_page(
	struct address_space	*mapping,
	pgoff_t			index,
	xfs_iomap_t		*iomapp,
	xfs_buf_t		*pb,
	unsigned long		max_offset,
	unsigned long		*fsbs,
	unsigned int            bbits)
{
	struct page		*page;

	page = find_trylock_page(mapping, index);
	if (!page)
		return NULL;
	if (PageWriteback(page))
		goto out;

	if (page->mapping && page_has_buffers(page)) {
		struct buffer_head	*bh, *head;
		unsigned long		p_offset = 0;

		*fsbs = 0;
		bh = head = page_buffers(page);
		do {
			if (!buffer_unwritten(bh) || !buffer_uptodate(bh))
				break;
			if (!xfs_offset_to_map(page, iomapp, p_offset))
				break;
			if (p_offset >= max_offset)
				break;
			xfs_map_at_offset(page, bh, p_offset, bbits, iomapp);
			set_buffer_unwritten_io(bh);
			bh->b_private = pb;
			p_offset += bh->b_size;
			(*fsbs)++;
		} while ((bh = bh->b_this_page) != head);

		if (p_offset)
			return page;
	}

out:
	unlock_page(page);
	return NULL;
}

/*
 * Look for a page at index which is unlocked and not mapped
 * yet - clustering for mmap write case.
 */
STATIC unsigned int
xfs_probe_unmapped_page(
	struct address_space	*mapping,
	pgoff_t			index,
	unsigned int		pg_offset)
{
	struct page		*page;
	int			ret = 0;

	page = find_trylock_page(mapping, index);
	if (!page)
		return 0;
	if (PageWriteback(page))
		goto out;

	if (page->mapping && PageDirty(page)) {
		if (page_has_buffers(page)) {
			struct buffer_head	*bh, *head;

			bh = head = page_buffers(page);
			do {
				if (buffer_mapped(bh) || !buffer_uptodate(bh))
					break;
				ret += bh->b_size;
				if (ret >= pg_offset)
					break;
			} while ((bh = bh->b_this_page) != head);
		} else
			ret = PAGE_CACHE_SIZE;
	}

out:
	unlock_page(page);
	return ret;
}

STATIC unsigned int
xfs_probe_unmapped_cluster(
	struct inode		*inode,
	struct page		*startpage,
	struct buffer_head	*bh,
	struct buffer_head	*head)
{
	pgoff_t			tindex, tlast, tloff;
	unsigned int		pg_offset, len, total = 0;
	struct address_space	*mapping = inode->i_mapping;

	/* First sum forwards in this page */
	do {
		if (buffer_mapped(bh))
			break;
		total += bh->b_size;
	} while ((bh = bh->b_this_page) != head);

	/* If we reached the end of the page, sum forwards in
	 * following pages.
	 */
	if (bh == head) {
		tlast = i_size_read(inode) >> PAGE_CACHE_SHIFT;
		/* Prune this back to avoid pathological behavior */
		tloff = min(tlast, startpage->index + 64);
		for (tindex = startpage->index + 1; tindex < tloff; tindex++) {
			len = xfs_probe_unmapped_page(mapping, tindex,
							PAGE_CACHE_SIZE);
			if (!len)
				return total;
			total += len;
		}
		if (tindex == tlast &&
		    (pg_offset = i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
			total += xfs_probe_unmapped_page(mapping,
							tindex, pg_offset);
		}
	}
	return total;
}

/*
 * Probe for a given page (index) in the inode and test if it is delayed
 * and without unwritten buffers.  Returns page locked and with an extra
 * reference count.
 */
STATIC struct page *
xfs_probe_delalloc_page(
	struct inode		*inode,
	pgoff_t			index)
{
	struct page		*page;

	page = find_trylock_page(inode->i_mapping, index);
	if (!page)
		return NULL;
	if (PageWriteback(page))
		goto out;

	if (page->mapping && page_has_buffers(page)) {
		struct buffer_head	*bh, *head;
		int			acceptable = 0;

		bh = head = page_buffers(page);
		do {
			if (buffer_unwritten(bh)) {
				acceptable = 0;
				break;
			} else if (buffer_delay(bh)) {
				acceptable = 1;
			}
		} while ((bh = bh->b_this_page) != head);

		if (acceptable)
			return page;
	}

out:
	unlock_page(page);
	return NULL;
}

STATIC int
xfs_map_unwritten(
	struct inode		*inode,
	struct page		*start_page,
	struct buffer_head	*head,
	struct buffer_head	*curr,
	unsigned long		p_offset,
	int			block_bits,
	xfs_iomap_t		*iomapp,
	struct writeback_control *wbc,
	int			startio,
	int			all_bh)
{
	struct buffer_head	*bh = curr;
	xfs_iomap_t		*tmp;
	xfs_buf_t		*pb;
	loff_t			offset, size;
	unsigned long		nblocks = 0;

	offset = start_page->index;
	offset <<= PAGE_CACHE_SHIFT;
	offset += p_offset;

	/* get an "empty" pagebuf to manage IO completion
	 * Proper values will be set before returning */
	pb = pagebuf_lookup(iomapp->iomap_target, 0, 0, 0);
	if (!pb)
		return -EAGAIN;

	/* Take a reference to the inode to prevent it from
	 * being reclaimed while we have outstanding unwritten
	 * extent IO on it.
	 */
	if ((igrab(inode)) != inode) {
		pagebuf_free(pb);
		return -EAGAIN;
	}

	/* 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);

	/* First map forwards in the page consecutive buffers
	 * covering this unwritten extent
	 */
	do {
		if (!buffer_unwritten(bh))
			break;
		tmp = xfs_offset_to_map(start_page, iomapp, p_offset);
		if (!tmp)
			break;
		xfs_map_at_offset(start_page, bh, p_offset, block_bits, iomapp);
		set_buffer_unwritten_io(bh);
		bh->b_private = pb;
		p_offset += bh->b_size;
		nblocks++;
	} while ((bh = bh->b_this_page) != head);

	atomic_add(nblocks, &pb->pb_io_remaining);

	/* If we reached the end of the page, map forwards in any
	 * following pages which are also covered by this extent.
	 */
	if (bh == head) {
		struct address_space	*mapping = inode->i_mapping;
		pgoff_t			tindex, tloff, tlast;
		unsigned long		bs;
		unsigned int		pg_offset, bbits = inode->i_blkbits;
		struct page		*page;

		tlast = i_size_read(inode) >> PAGE_CACHE_SHIFT;
		tloff = (iomapp->iomap_offset + iomapp->iomap_bsize) >> PAGE_CACHE_SHIFT;
		tloff = min(tlast, tloff);
		for (tindex = start_page->index + 1; tindex < tloff; tindex++) {
			page = xfs_probe_unwritten_page(mapping,
						tindex, iomapp, pb,
						PAGE_CACHE_SIZE, &bs, bbits);
			if (!page)
				break;
			nblocks += bs;
			atomic_add(bs, &pb->pb_io_remaining);
			xfs_convert_page(inode, page, iomapp, wbc, pb,
							startio, all_bh);
			/* stop if converting the next page might add
			 * enough blocks that the corresponding byte
			 * count won't fit in our ulong page buf length */
			if (nblocks >= ((ULONG_MAX - PAGE_SIZE) >> block_bits))
				goto enough;
		}

		if (tindex == tlast &&
		    (pg_offset = (i_size_read(inode) & (PAGE_CACHE_SIZE - 1)))) {
			page = xfs_probe_unwritten_page(mapping,
							tindex, iomapp, pb,
							pg_offset, &bs, bbits);
			if (page) {
				nblocks += bs;
				atomic_add(bs, &pb->pb_io_remaining);
				xfs_convert_page(inode, page, iomapp, wbc, pb,
							startio, all_bh);
				if (nblocks >= ((ULONG_MAX - PAGE_SIZE) >> block_bits))
					goto enough;
			}
		}
	}

enough:
	size = nblocks;		/* NB: using 64bit number here */
	size <<= block_bits;	/* convert fsb's to byte range */

	XFS_BUF_DATAIO(pb);
	XFS_BUF_ASYNC(pb);
	XFS_BUF_SET_SIZE(pb, size);
	XFS_BUF_SET_COUNT(pb, size);
	XFS_BUF_SET_OFFSET(pb, offset);
	XFS_BUF_SET_FSPRIVATE(pb, LINVFS_GET_VP(inode));
	XFS_BUF_SET_IODONE_FUNC(pb, linvfs_unwritten_convert);

	if (atomic_dec_and_test(&pb->pb_io_remaining) == 1) {
		pagebuf_iodone(pb, 1, 1);
	}

	return 0;
}

STATIC void
xfs_submit_page(
	struct page		*page,
	struct writeback_control *wbc,
	struct buffer_head	*bh_arr[],
	int			bh_count,
	int			probed_page,
	int			clear_dirty)
{
	struct buffer_head	*bh;
	int			i;

	BUG_ON(PageWriteback(page));
	if (bh_count)
		set_page_writeback(page);
	if (clear_dirty)
		clear_page_dirty(page);
	unlock_page(page);

	if (bh_count) {
		for (i = 0; i < bh_count; i++) {
			bh = bh_arr[i];
			mark_buffer_async_write(bh);
			if (buffer_unwritten(bh))
				set_buffer_unwritten_io(bh);
			set_buffer_uptodate(bh);
			clear_buffer_dirty(bh);
		}

		for (i = 0; i < bh_count; i++)
			submit_bh(WRITE, bh_arr[i]);

		if (probed_page && clear_dirty)
			wbc->nr_to_write--;	/* Wrote an "extra" page */
	}
}

/*
 * Allocate & map buffers for page given the extent map. Write it out.
 * except for the original page of a writepage, this is called on
 * delalloc/unwritten pages only, for the original page it is possible
 * that the page has no mapping at all.
 */
STATIC void
xfs_convert_page(
	struct inode		*inode,
	struct page		*page,
	xfs_iomap_t		*iomapp,
	struct writeback_control *wbc,
	void			*private,
	int			startio,
	int			all_bh)
{
	struct buffer_head	*bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
	xfs_iomap_t		*mp = iomapp, *tmp;
	unsigned long		offset, end_offset;
	int			index = 0;
	int			bbits = inode->i_blkbits;
	int			len, page_dirty;

	end_offset = (i_size_read(inode) & (PAGE_CACHE_SIZE - 1));

	/*
	 * page_dirty is initially a count of buffers on the page before
	 * EOF and is decrememted as we move each into a cleanable state.
	 */
	len = 1 << inode->i_blkbits;
	end_offset = max(end_offset, PAGE_CACHE_SIZE);
	end_offset = roundup(end_offset, len);
	page_dirty = end_offset / len;

	offset = 0;
	bh = head = page_buffers(page);
	do {
		if (offset >= end_offset)
			break;
		if (!(PageUptodate(page) || buffer_uptodate(bh)))
			continue;
		if (buffer_mapped(bh) && all_bh &&
		    !(buffer_unwritten(bh) || buffer_delay(bh))) {
			if (startio) {
				lock_buffer(bh);
				bh_arr[index++] = bh;
				page_dirty--;
			}
			continue;
		}
		tmp = xfs_offset_to_map(page, mp, offset);
		if (!tmp)
			continue;
		ASSERT(!(tmp->iomap_flags & IOMAP_HOLE));
		ASSERT(!(tmp->iomap_flags & IOMAP_DELAY));

		/* If this is a new unwritten extent buffer (i.e. one
		 * that we haven't passed in private data for, we must
		 * now map this buffer too.
		 */
		if (buffer_unwritten(bh) && !bh->b_end_io) {
			ASSERT(tmp->iomap_flags & IOMAP_UNWRITTEN);
			xfs_map_unwritten(inode, page, head, bh, offset,
					bbits, tmp, wbc, startio, all_bh);
		} else if (! (buffer_unwritten(bh) && buffer_locked(bh))) {
			xfs_map_at_offset(page, bh, offset, bbits, tmp);
			if (buffer_unwritten(bh)) {
				set_buffer_unwritten_io(bh);
				bh->b_private = private;
				ASSERT(private);
			}
		}
		if (startio) {
			bh_arr[index++] = bh;
		} else {
			set_buffer_dirty(bh);
			unlock_buffer(bh);
			mark_buffer_dirty(bh);
		}
		page_dirty--;
	} while (offset += len, (bh = bh->b_this_page) != head);

	if (startio && index) {
		xfs_submit_page(page, wbc, bh_arr, index, 1, !page_dirty);
	} else {
		unlock_page(page);
	}
}

/*
 * Convert & write out a cluster of pages in the same extent as defined
 * by mp and following the start page.
 */
STATIC void
xfs_cluster_write(
	struct inode		*inode,
	pgoff_t			tindex,
	xfs_iomap_t		*iomapp,
	struct writeback_control *wbc,
	int			startio,
	int			all_bh,
	pgoff_t			tlast)
{
	struct page		*page;

	for (; tindex <= tlast; tindex++) {
		page = xfs_probe_delalloc_page(inode, tindex);
		if (!page)
			break;
		xfs_convert_page(inode, page, iomapp, wbc, NULL,
				startio, all_bh);
	}
}

/*
 * Calling this without startio set means we are being asked to make a dirty
 * page ready for freeing it's buffers.  When called with startio set then
 * we are coming from writepage.
 *
 * When called with startio set it is important that we write the WHOLE
 * page if possible.
 * The bh->b_state's cannot know if any of the blocks or which block for
 * that matter are dirty due to mmap writes, and therefore bh uptodate is
 * only vaild if the page itself isn't completely uptodate.  Some layers
 * may clear the page dirty flag prior to calling write page, under the
 * assumption the entire page will be written out; by not writing out the
 * whole page the page can be reused before all valid dirty data is
 * written out.  Note: in the case of a page that has been dirty'd by
 * mapwrite and but partially setup by block_prepare_write the
 * bh->b_states's will not agree and only ones setup by BPW/BCW will have
 * valid state, thus the whole page must be written out thing.
 */

STATIC int
xfs_page_state_convert(
	struct inode	*inode,
	struct page	*page,
	struct writeback_control *wbc,
	int		startio,
	int		unmapped) /* also implies page uptodate */
{
	struct buffer_head	*bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
	xfs_iomap_t		*iomp, iomap;
	loff_t			offset;
	unsigned long           p_offset = 0;
	__uint64_t              end_offset;
	pgoff_t                 end_index, last_index, tlast;
	int			len, err, i, cnt = 0, uptodate = 1;
	int			flags;
	int			page_dirty;

	/* wait for other IO threads? */
	flags = (startio && wbc->sync_mode != WB_SYNC_NONE) ? 0 : BMAPI_TRYLOCK;

	/* Is this page beyond the end of the file? */
	offset = i_size_read(inode);
	end_index = offset >> PAGE_CACHE_SHIFT;
	last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
	if (page->index >= end_index) {
		if ((page->index >= end_index + 1) ||
		    !(i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
			err = -EIO;
			goto error;
		}
	}

	end_offset = min_t(unsigned long long,
			(loff_t)(page->index + 1) << PAGE_CACHE_SHIFT, offset);
	offset = (loff_t)page->index << PAGE_CACHE_SHIFT;

	/*
	 * page_dirty is initially a count of buffers on the page before
	 * EOF and is decrememted as we move each into a cleanable state.
	 */
	len = 1 << inode->i_blkbits;
	p_offset = max(p_offset, PAGE_CACHE_SIZE);
	p_offset = roundup(p_offset, len);
	page_dirty = p_offset / len;

	iomp = NULL;
	p_offset = 0;
	bh = head = page_buffers(page);

	do {
		if (offset >= end_offset)
			break;
		if (!buffer_uptodate(bh))
			uptodate = 0;
		if (!(PageUptodate(page) || buffer_uptodate(bh)) && !startio)
			continue;

		if (iomp) {
			iomp = xfs_offset_to_map(page, &iomap, p_offset);
		}

		/*
		 * First case, map an unwritten extent and prepare for
		 * extent state conversion transaction on completion.
		 */
		if (buffer_unwritten(bh)) {
			if (!startio)
				continue;
			if (!iomp) {
				err = xfs_map_blocks(inode, offset, len, &iomap,
						BMAPI_READ|BMAPI_IGNSTATE);
				if (err) {
					goto error;
				}
				iomp = xfs_offset_to_map(page, &iomap,
								p_offset);
			}
			if (iomp) {
				if (!bh->b_end_io) {
					err = xfs_map_unwritten(inode, page,
							head, bh, p_offset,
							inode->i_blkbits, iomp,
							wbc, startio, unmapped);
					if (err) {
						goto error;
					}
				} else {
					set_bit(BH_Lock, &bh->b_state);
				}
				BUG_ON(!buffer_locked(bh));
				bh_arr[cnt++] = bh;
				page_dirty--;
			}
		/*
		 * Second case, allocate space for a delalloc buffer.
		 * We can return EAGAIN here in the release page case.
		 */
		} else if (buffer_delay(bh)) {
			if (!iomp) {
				err = xfs_map_blocks(inode, offset, len, &iomap,
						BMAPI_ALLOCATE | flags);
				if (err) {
					goto error;
				}
				iomp = xfs_offset_to_map(page, &iomap,
								p_offset);
			}
			if (iomp) {
				xfs_map_at_offset(page, bh, p_offset,
						inode->i_blkbits, iomp);
				if (startio) {
					bh_arr[cnt++] = bh;
				} else {
					set_buffer_dirty(bh);
					unlock_buffer(bh);
					mark_buffer_dirty(bh);
				}
				page_dirty--;
			}
		} else if ((buffer_uptodate(bh) || PageUptodate(page)) &&
			   (unmapped || startio)) {

			if (!buffer_mapped(bh)) {
				int	size;

				/*
				 * Getting here implies an unmapped buffer
				 * was found, and we are in a path where we
				 * need to write the whole page out.
				 */
				if (!iomp) {
					size = xfs_probe_unmapped_cluster(
							inode, page, bh, head);
					err = xfs_map_blocks(inode, offset,
							size, &iomap,
							BMAPI_WRITE|BMAPI_MMAP);
					if (err) {
						goto error;
					}
					iomp = xfs_offset_to_map(page, &iomap,
								     p_offset);
				}
				if (iomp) {
					xfs_map_at_offset(page,
							bh, p_offset,
							inode->i_blkbits, iomp);
					if (startio) {
						bh_arr[cnt++] = bh;
					} else {
						set_buffer_dirty(bh);
						unlock_buffer(bh);
						mark_buffer_dirty(bh);
					}
					page_dirty--;
				}
			} else if (startio) {
				if (buffer_uptodate(bh) &&
				    !test_and_set_bit(BH_Lock, &bh->b_state)) {
					bh_arr[cnt++] = bh;
					page_dirty--;
				}
			}
		}
	} while (offset += len, p_offset += len,
		((bh = bh->b_this_page) != head));

	if (uptodate && bh == head)
		SetPageUptodate(page);

	if (startio) {
		WARN_ON(page_dirty);
		xfs_submit_page(page, wbc, bh_arr, cnt, 0, !page_dirty);
	}

	if (iomp) {
		offset = (iomp->iomap_offset + iomp->iomap_bsize - 1) >>
					PAGE_CACHE_SHIFT;
		tlast = min_t(pgoff_t, offset, last_index);
		xfs_cluster_write(inode, page->index + 1, iomp, wbc,
					startio, unmapped, tlast);
	}

	return page_dirty;

error:
	for (i = 0; i < cnt; i++) {
		unlock_buffer(bh_arr[i]);
	}

	/*
	 * If it's delalloc and we have nowhere to put it,
	 * throw it away, unless the lower layers told
	 * us to try again.
	 */
	if (err != -EAGAIN) {
		if (!unmapped) {
			block_invalidatepage(page, 0);
		}
		ClearPageUptodate(page);
	}
	return err;
}

STATIC int
__linvfs_get_block(
	struct inode		*inode,
	sector_t		iblock,
	unsigned long		blocks,
	struct buffer_head	*bh_result,
	int			create,
	int			direct,
	bmapi_flags_t		flags)
{
	vnode_t			*vp = LINVFS_GET_VP(inode);
	xfs_iomap_t		iomap;
	int			retpbbm = 1;
	int			error;
	ssize_t			size;
	loff_t			offset = (loff_t)iblock << inode->i_blkbits;

	if (blocks)
		size = blocks << inode->i_blkbits;
	else
		size = 1 << inode->i_blkbits;

	VOP_BMAP(vp, offset, size,
		create ? flags : BMAPI_READ, &iomap, &retpbbm, error);
	if (error)
		return -error;

	if (retpbbm == 0)
		return 0;

	if (iomap.iomap_bn != IOMAP_DADDR_NULL) {
		xfs_daddr_t		bn;
		loff_t			delta;

		/* For unwritten extents do not report a disk address on
		 * the read case (treat as if we're reading into a hole).
		 */
		if (create || !(iomap.iomap_flags & IOMAP_UNWRITTEN)) {
			delta = offset - iomap.iomap_offset;
			delta >>= inode->i_blkbits;

			bn = iomap.iomap_bn >> (inode->i_blkbits - BBSHIFT);
			bn += delta;
			BUG_ON(!bn && !(iomap.iomap_flags & IOMAP_REALTIME));
			bh_result->b_blocknr = bn;
			set_buffer_mapped(bh_result);
		}
		if (create && (iomap.iomap_flags & IOMAP_UNWRITTEN)) {
			if (direct)
				bh_result->b_private = inode;
			set_buffer_unwritten(bh_result);
			set_buffer_delay(bh_result);
		}
	}

	/* If this is a realtime file, data might be on a new device */
	bh_result->b_bdev = iomap.iomap_target->pbr_bdev;

	/* If we previously allocated a block out beyond eof and
	 * we are now coming back to use it then we will need to
	 * flag it as new even if it has a disk address.
	 */
	if (create &&
	    ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||
	     (offset >= i_size_read(inode)) || (iomap.iomap_flags & IOMAP_NEW))) {
		set_buffer_new(bh_result);
	}

	if (iomap.iomap_flags & IOMAP_DELAY) {
		BUG_ON(direct);
		if (create) {
			set_buffer_uptodate(bh_result);
			set_buffer_mapped(bh_result);
			set_buffer_delay(bh_result);
		}
	}

	if (blocks) {
		bh_result->b_size = (ssize_t)min(
			(loff_t)(iomap.iomap_bsize - iomap.iomap_delta),
			(loff_t)(blocks << inode->i_blkbits));
	}

	return 0;
}

int
linvfs_get_block(
	struct inode		*inode,
	sector_t		iblock,
	struct buffer_head	*bh_result,
	int			create)
{
	return __linvfs_get_block(inode, iblock, 0, bh_result,
					create, 0, BMAPI_WRITE);
}

STATIC int
linvfs_get_blocks_direct(
	struct inode		*inode,
	sector_t		iblock,
	unsigned long		max_blocks,
	struct buffer_head	*bh_result,
	int			create)
{
	return __linvfs_get_block(inode, iblock, max_blocks, bh_result,
					create, 1, BMAPI_WRITE|BMAPI_DIRECT);
}

STATIC ssize_t
linvfs_direct_IO(
	int			rw,
	struct kiocb		*iocb,
	const struct iovec	*iov,
	loff_t			offset,
	unsigned long		nr_segs)
{
	struct file	*file = iocb->ki_filp;
	struct inode	*inode = file->f_mapping->host;
	vnode_t		*vp = LINVFS_GET_VP(inode);
	xfs_iomap_t	iomap;
	int		maps = 1;
	int		error;

	VOP_BMAP(vp, offset, 0, BMAPI_DEVICE, &iomap, &maps, error);
	if (error)
		return -error;

	return blockdev_direct_IO_own_locking(rw, iocb, inode,
		iomap.iomap_target->pbr_bdev,
		iov, offset, nr_segs,
		linvfs_get_blocks_direct,
		linvfs_unwritten_convert_direct);
}


STATIC sector_t
linvfs_bmap(
	struct address_space	*mapping,
	sector_t		block)
{
	struct inode		*inode = (struct inode *)mapping->host;
	vnode_t			*vp = LINVFS_GET_VP(inode);
	int			error;

	vn_trace_entry(vp, "linvfs_bmap", (inst_t *)__return_address);

	VOP_RWLOCK(vp, VRWLOCK_READ);
	VOP_FLUSH_PAGES(vp, (xfs_off_t)0, -1, 0, FI_REMAPF, error);
	VOP_RWUNLOCK(vp, VRWLOCK_READ);
	return generic_block_bmap(mapping, block, linvfs_get_block);
}

STATIC int
linvfs_readpage(
	struct file		*unused,
	struct page		*page)
{
	return mpage_readpage(page, linvfs_get_block);
}

STATIC int
linvfs_readpages(
	struct file		*unused,
	struct address_space	*mapping,
	struct list_head	*pages,
	unsigned		nr_pages)
{
	return mpage_readpages(mapping, pages, nr_pages, linvfs_get_block);
}

STATIC void
xfs_count_page_state(
	struct page		*page,
	int			*delalloc,
	int			*unmapped,
	int			*unwritten)
{
	struct buffer_head	*bh, *head;

	*delalloc = *unmapped = *unwritten = 0;

	bh = head = page_buffers(page);
	do {
		if (buffer_uptodate(bh) && !buffer_mapped(bh))
			(*unmapped) = 1;
		else if (buffer_unwritten(bh) && !buffer_delay(bh))
			clear_buffer_unwritten(bh);
		else if (buffer_unwritten(bh))
			(*unwritten) = 1;
		else if (buffer_delay(bh))
			(*delalloc) = 1;
	} while ((bh = bh->b_this_page) != head);
}


/*
 * writepage: Called from one of two places:
 *
 * 1. we are flushing a delalloc buffer head.
 *
 * 2. we are writing out a dirty page. Typically the page dirty
 *    state is cleared before we get here. In this case is it
 *    conceivable we have no buffer heads.
 *
 * For delalloc space on the page we need to allocate space and
 * flush it. For unmapped buffer heads on the page we should
 * allocate space if the page is uptodate. For any other dirty
 * buffer heads on the page we should flush them.
 *
 * If we detect that a transaction would be required to flush
 * the page, we have to check the process flags first, if we
 * are already in a transaction or disk I/O during allocations
 * is off, we need to fail the writepage and redirty the page.
 */

STATIC int
linvfs_writepage(
	struct page		*page,
	struct writeback_control *wbc)
{
	int			error;
	int			need_trans;
	int			delalloc, unmapped, unwritten;
	struct inode		*inode = page->mapping->host;

	xfs_page_trace(XFS_WRITEPAGE_ENTER, inode, page, 0);

	/*
	 * We need a transaction if:
	 *  1. There are delalloc buffers on the page
	 *  2. The page is uptodate and we have unmapped buffers
	 *  3. The page is uptodate and we have no buffers
	 *  4. There are unwritten buffers on the page
	 */

	if (!page_has_buffers(page)) {
		unmapped = 1;
		need_trans = 1;
	} else {
		xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
		if (!PageUptodate(page))
			unmapped = 0;
		need_trans = delalloc + unmapped + unwritten;
	}

	/*
	 * If we need a transaction and the process flags say
	 * we are already in a transaction, or no IO is allowed
	 * then mark the page dirty again and leave the page
	 * as is.
	 */
	if (PFLAGS_TEST_FSTRANS() && need_trans)
		goto out_fail;

	/*
	 * Delay hooking up buffer heads until we have
	 * made our go/no-go decision.
	 */
	if (!page_has_buffers(page))
		create_empty_buffers(page, 1 << inode->i_blkbits, 0);

	/*
	 * Convert delayed allocate, unwritten or unmapped space
	 * to real space and flush out to disk.
	 */
	error = xfs_page_state_convert(inode, page, wbc, 1, unmapped);
	if (error == -EAGAIN)
		goto out_fail;
	if (unlikely(error < 0))
		goto out_unlock;

	return 0;

out_fail:
	redirty_page_for_writepage(wbc, page);
	unlock_page(page);
	return 0;
out_unlock:
	unlock_page(page);
	return error;
}

/*
 * Called to move a page into cleanable state - and from there
 * to be released. Possibly the page is already clean. We always
 * have buffer heads in this call.
 *
 * Returns 0 if the page is ok to release, 1 otherwise.
 *
 * Possible scenarios are:
 *
 * 1. We are being called to release a page which has been written
 *    to via regular I/O. buffer heads will be dirty and possibly
 *    delalloc. If no delalloc buffer heads in this case then we
 *    can just return zero.
 *
 * 2. We are called to release a page which has been written via
 *    mmap, all we need to do is ensure there is no delalloc
 *    state in the buffer heads, if not we can let the caller
 *    free them and we should come back later via writepage.
 */
STATIC int
linvfs_release_page(
	struct page		*page,
	int			gfp_mask)
{
	struct inode		*inode = page->mapping->host;
	int			dirty, delalloc, unmapped, unwritten;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_ALL,
		.nr_to_write = 1,
	};

	xfs_page_trace(XFS_RELEASEPAGE_ENTER, inode, page, gfp_mask);

	xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
	if (!delalloc && !unwritten)
		goto free_buffers;

	if (!(gfp_mask & __GFP_FS))
		return 0;

	/* If we are already inside a transaction or the thread cannot
	 * do I/O, we cannot release this page.
	 */
	if (PFLAGS_TEST_FSTRANS())
		return 0;

	/*
	 * Convert delalloc space to real space, do not flush the
	 * data out to disk, that will be done by the caller.
	 * Never need to allocate space here - we will always
	 * come back to writepage in that case.
	 */
	dirty = xfs_page_state_convert(inode, page, &wbc, 0, 0);
	if (dirty == 0 && !unwritten)
		goto free_buffers;
	return 0;

free_buffers:
	return try_to_free_buffers(page);
}

STATIC int
linvfs_prepare_write(
	struct file		*file,
	struct page		*page,
	unsigned int		from,
	unsigned int		to)
{
	return block_prepare_write(page, from, to, linvfs_get_block);
}

struct address_space_operations linvfs_aops = {
	.readpage		= linvfs_readpage,
	.readpages		= linvfs_readpages,
	.writepage		= linvfs_writepage,
	.sync_page		= block_sync_page,
	.releasepage		= linvfs_release_page,
	.prepare_write		= linvfs_prepare_write,
	.commit_write		= generic_commit_write,
	.bmap			= linvfs_bmap,
	.direct_IO		= linvfs_direct_IO,
};