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Make absolutely sure we don't attempt to access beyond the end of the
maximum file size limit.  This could happen previously with the space
alloc heuristic for delalloc beyond the end of file.

/*
 * Copyright (c) 2000-2003 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_fs.h"
#include "xfs_inum.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dir.h"
#include "xfs_dir2.h"
#include "xfs_alloc.h"
#include "xfs_dmapi.h"
#include "xfs_quota.h"
#include "xfs_mount.h"
#include "xfs_alloc_btree.h"
#include "xfs_bmap_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_btree.h"
#include "xfs_ialloc.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_bmap.h"
#include "xfs_bit.h"
#include "xfs_rtalloc.h"
#include "xfs_error.h"
#include "xfs_itable.h"
#include "xfs_rw.h"
#include "xfs_acl.h"
#include "xfs_cap.h"
#include "xfs_mac.h"
#include "xfs_attr.h"
#include "xfs_buf_item.h"
#include "xfs_trans_space.h"
#include "xfs_utils.h"

#define XFS_WRITEIO_ALIGN(mp,off)	(((off) >> mp->m_writeio_log) \
						<< mp->m_writeio_log)
#define XFS_STRAT_WRITE_IMAPS	2
#define XFS_WRITE_IMAPS		XFS_BMAP_MAX_NMAP

STATIC int
_xfs_imap_to_bmap(
	xfs_iocore_t	*io,
	xfs_off_t	offset,
	xfs_bmbt_irec_t *imap,
	page_buf_bmap_t	*pbmapp,
	int		imaps,			/* Number of imap entries */
	int		pbmaps)			/* Number of pbmap entries */
{
	xfs_mount_t	*mp;
	xfs_fsize_t	nisize;
	int		pbm;
	xfs_fsblock_t	start_block;

	mp = io->io_mount;
	nisize = XFS_SIZE(mp, io);
	if (io->io_new_size > nisize)
		nisize = io->io_new_size;

	for (pbm = 0; imaps && pbm < pbmaps; imaps--, pbmapp++, imap++, pbm++) {
		pbmapp->pbm_target = io->io_flags & XFS_IOCORE_RT ?
			mp->m_rtdev_targp : mp->m_ddev_targp;
		pbmapp->pbm_offset = XFS_FSB_TO_B(mp, imap->br_startoff);
		pbmapp->pbm_delta = offset - pbmapp->pbm_offset;
		pbmapp->pbm_bsize = XFS_FSB_TO_B(mp, imap->br_blockcount);
		pbmapp->pbm_flags = 0;

		start_block = imap->br_startblock;
		if (start_block == HOLESTARTBLOCK) {
			pbmapp->pbm_bn = PAGE_BUF_DADDR_NULL;
			pbmapp->pbm_flags = PBMF_HOLE;
		} else if (start_block == DELAYSTARTBLOCK) {
			pbmapp->pbm_bn = PAGE_BUF_DADDR_NULL;
			pbmapp->pbm_flags = PBMF_DELAY;
		} else {
			pbmapp->pbm_bn = XFS_FSB_TO_DB_IO(io, start_block);
			if (ISUNWRITTEN(imap))
				pbmapp->pbm_flags |= PBMF_UNWRITTEN;
		}

		if ((pbmapp->pbm_offset + pbmapp->pbm_bsize) >= nisize) {
			pbmapp->pbm_flags |= PBMF_EOF;
		}

		offset += pbmapp->pbm_bsize - pbmapp->pbm_delta;
	}
	return pbm;	/* Return the number filled */
}

int
xfs_iomap(
	xfs_iocore_t	*io,
	xfs_off_t	offset,
	ssize_t		count,
	int		flags,
	page_buf_bmap_t	*pbmapp,
	int		*npbmaps)
{
	xfs_mount_t	*mp = io->io_mount;
	xfs_fileoff_t	offset_fsb, end_fsb;
	int		error = 0;
	int		lockmode = 0;
	xfs_bmbt_irec_t	imap;
	int		nimaps = 1;
	int		bmap_flags = 0;

	if (XFS_FORCED_SHUTDOWN(mp))
		return XFS_ERROR(EIO);

	switch (flags &
		(BMAP_READ|BMAP_WRITE|BMAP_ALLOCATE|BMAP_UNWRITTEN)) {
	case BMAP_READ:
		lockmode = XFS_LCK_MAP_SHARED(mp, io);
		bmap_flags = XFS_BMAPI_ENTIRE;
		if (flags & BMAP_IGNSTATE)
			bmap_flags |= XFS_BMAPI_IGSTATE;
		break;
	case PBF_WRITE:
		lockmode = XFS_ILOCK_EXCL|XFS_EXTSIZE_WR;
		bmap_flags = 0;
		XFS_ILOCK(mp, io, lockmode);
		break;
	case BMAP_ALLOCATE:
		lockmode = XFS_ILOCK_SHARED|XFS_EXTSIZE_RD;
		bmap_flags = XFS_BMAPI_ENTIRE;
		/* Attempt non-blocking lock */
		if (flags & BMAP_TRYLOCK) {
			if (!XFS_ILOCK_NOWAIT(mp, io, lockmode))
				return XFS_ERROR(EAGAIN);
		} else {
			XFS_ILOCK(mp, io, lockmode);
		}
		break;
	case BMAP_UNWRITTEN:
		goto phase2;
	default:
		BUG();
	}

	ASSERT(offset <= mp->m_maxioffset);
	if ((xfs_fsize_t)offset + count > mp->m_maxioffset)
		count = mp->m_maxioffset - offset;
	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
	offset_fsb = XFS_B_TO_FSBT(mp, offset);

	error = XFS_BMAPI(mp, NULL, io, offset_fsb,
			(xfs_filblks_t)(end_fsb - offset_fsb) ,
			bmap_flags,  NULL, 0, &imap,
			&nimaps, NULL);

	if (error)
		goto out;

phase2:
	switch (flags & (BMAP_WRITE|BMAP_ALLOCATE|BMAP_UNWRITTEN)) {
	case BMAP_WRITE:
		/* If we found an extent, return it */
		if (nimaps && (imap.br_startblock != HOLESTARTBLOCK))
			break;

		if (flags & (BMAP_DIRECT|BMAP_MMAP)) {
			error = XFS_IOMAP_WRITE_DIRECT(mp, io, offset,
					count, flags, &imap, &nimaps, nimaps);
		} else {
			error = XFS_IOMAP_WRITE_DELAY(mp, io, offset, count,
					flags, &imap, &nimaps);
		}
		break;
	case BMAP_ALLOCATE:
		/* If we found an extent, return it */
		XFS_IUNLOCK(mp, io, lockmode);
		lockmode = 0;

		if (nimaps && !ISNULLSTARTBLOCK(imap.br_startblock))
			break;

		error = XFS_IOMAP_WRITE_ALLOCATE(mp, io, &imap, &nimaps);
		break;
	case BMAP_UNWRITTEN:
		lockmode = 0;
		error = XFS_IOMAP_WRITE_UNWRITTEN(mp, io, offset, count);
		nimaps = 0;
		break;
	}

	if (nimaps) {
		*npbmaps = _xfs_imap_to_bmap(io, offset, &imap,
						pbmapp, nimaps, *npbmaps);
	} else if (npbmaps) {
		*npbmaps = 0;
	}

out:
	if (lockmode)
		XFS_IUNLOCK(mp, io, lockmode);
	return XFS_ERROR(error);
}

STATIC int
xfs_flush_space(
	xfs_inode_t	*ip,
	int		*fsynced,
	int		*ioflags)
{
	vnode_t		*vp = XFS_ITOV(ip);

	switch (*fsynced) {
	case 0:
		if (ip->i_delayed_blks) {
			xfs_iunlock(ip, XFS_ILOCK_EXCL);
			fsync_inode_data_buffers(LINVFS_GET_IP(vp));
			xfs_ilock(ip, XFS_ILOCK_EXCL);
			*fsynced = 1;
		} else {
			*ioflags |= BMAP_SYNC;
			*fsynced = 2;
		}
		return 0;
	case 1:
		*fsynced = 2;
		*ioflags |= BMAP_SYNC;
		return 0;
	case 2:
		xfs_iunlock(ip, XFS_ILOCK_EXCL);
		fsync_no_super(LINVFS_GET_IP(vp)->i_dev);
		xfs_log_force(ip->i_mount, (xfs_lsn_t)0,
						XFS_LOG_FORCE|XFS_LOG_SYNC);
		xfs_ilock(ip, XFS_ILOCK_EXCL);
		*fsynced = 3;
		return 0;
	}
	return 1;
}

int
xfs_iomap_write_direct(
	xfs_inode_t	*ip,
	loff_t		offset,
	size_t		count,
	int		flags,
	xfs_bmbt_irec_t *ret_imap,
	int		*nmaps,
	int		found)
{
	xfs_mount_t	*mp = ip->i_mount;
	xfs_iocore_t	*io = &ip->i_iocore;
	xfs_fileoff_t	offset_fsb;
	xfs_fileoff_t	last_fsb;
	xfs_filblks_t	count_fsb;
	xfs_fsize_t	isize;
	xfs_fsblock_t	firstfsb;
	int		nimaps, maps;
	int		error;
	int		bmapi_flag;
	int		rt;
	xfs_trans_t	*tp;
	xfs_bmbt_irec_t imap[XFS_WRITE_IMAPS], *imapp;
	xfs_bmap_free_t free_list;
	int		aeof;
	xfs_filblks_t	datablocks;
	int		committed;
	int		numrtextents;
	uint		resblks;

	/*
	 * Make sure that the dquots are there. This doesn't hold
	 * the ilock across a disk read.
	 */

	error = XFS_QM_DQATTACH(ip->i_mount, ip, XFS_QMOPT_ILOCKED);
	if (error)
		return XFS_ERROR(error);

	maps = min(XFS_WRITE_IMAPS, *nmaps);
	nimaps = maps;

	isize = ip->i_d.di_size;
	aeof = (offset + count) > isize;

	if (io->io_new_size > isize)
		isize = io->io_new_size;

	offset_fsb = XFS_B_TO_FSBT(mp, offset);
	last_fsb = XFS_B_TO_FSB(mp, ((xfs_ufsize_t)(offset + count)));
	count_fsb = last_fsb - offset_fsb;
	if (found && (ret_imap->br_startblock == HOLESTARTBLOCK)) {
		xfs_fileoff_t	map_last_fsb;

		map_last_fsb = ret_imap->br_blockcount + ret_imap->br_startoff;

		if (map_last_fsb < last_fsb) {
			last_fsb = map_last_fsb;
			count_fsb = last_fsb - offset_fsb;
		}
		ASSERT(count_fsb > 0);
	}

	/*
	 * determine if reserving space on
	 * the data or realtime partition.
	 */
	if ((rt = XFS_IS_REALTIME_INODE(ip))) {
		int	sbrtextsize, iprtextsize;

		sbrtextsize = mp->m_sb.sb_rextsize;
		iprtextsize =
			ip->i_d.di_extsize ? ip->i_d.di_extsize : sbrtextsize;
		numrtextents = (count_fsb + iprtextsize - 1);
		do_div(numrtextents, sbrtextsize);
		datablocks = 0;
	} else {
		datablocks = count_fsb;
		numrtextents = 0;
	}

	/*
	 * allocate and setup the transaction
	 */
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	tp = xfs_trans_alloc(mp, XFS_TRANS_DIOSTRAT);

	resblks = XFS_DIOSTRAT_SPACE_RES(mp, datablocks);

	error = xfs_trans_reserve(tp, resblks,
			XFS_WRITE_LOG_RES(mp), numrtextents,
			XFS_TRANS_PERM_LOG_RES,
			XFS_WRITE_LOG_COUNT);

	/*
	 * check for running out of space
	 */
	if (error)
		/*
		 * Free the transaction structure.
		 */
		xfs_trans_cancel(tp, 0);

	xfs_ilock(ip, XFS_ILOCK_EXCL);

	if (error)
		goto error_out; /* Don't return in above if .. trans ..,
					need lock to return */

	if (XFS_TRANS_RESERVE_BLKQUOTA(mp, tp, ip, resblks)) {
		error = (EDQUOT);
		goto error1;
	}
	nimaps = 1;

	bmapi_flag = XFS_BMAPI_WRITE;
	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
	xfs_trans_ihold(tp, ip);

	if (!(flags & BMAP_MMAP) && (offset < ip->i_d.di_size || rt))
		bmapi_flag |= XFS_BMAPI_PREALLOC;

	/*
	 * issue the bmapi() call to allocate the blocks
	 */
	XFS_BMAP_INIT(&free_list, &firstfsb);
	imapp = &imap[0];
	error = xfs_bmapi(tp, ip, offset_fsb, count_fsb,
		bmapi_flag, &firstfsb, 0, imapp, &nimaps, &free_list);
	if (error) {
		goto error0;
	}

	/*
	 * complete the transaction
	 */

	error = xfs_bmap_finish(&tp, &free_list, firstfsb, &committed);
	if (error) {
		goto error0;
	}

	error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES, NULL);
	if (error) {
		goto error_out;
	}

	/* copy any maps to caller's array and return any error. */
	if (nimaps == 0) {
		error = (ENOSPC);
		goto error_out;
	}

	*ret_imap = imap[0];
	*nmaps = 1;
	return 0;

 error0:	/* Cancel bmap, unlock inode, and cancel trans */
	xfs_bmap_cancel(&free_list);

 error1:	/* Just cancel transaction */
	xfs_trans_cancel(tp, XFS_TRANS_RELEASE_LOG_RES | XFS_TRANS_ABORT);
	*nmaps = 0;	/* nothing set-up here */

error_out:
	return XFS_ERROR(error);
}

int
xfs_iomap_write_delay(
	xfs_inode_t	*ip,
	loff_t		offset,
	size_t		count,
	int		ioflag,
	xfs_bmbt_irec_t *ret_imap,
	int		*nmaps)
{
	xfs_mount_t	*mp = ip->i_mount;
	xfs_iocore_t	*io = &ip->i_iocore;
	xfs_fileoff_t	offset_fsb;
	xfs_fileoff_t	last_fsb;
	xfs_fsize_t	isize;
	xfs_fsblock_t	firstblock;
	int		nimaps;
	int		error;
	xfs_bmbt_irec_t imap[XFS_WRITE_IMAPS];
	int		aeof;
	int		fsynced = 0;

	ASSERT(ismrlocked(&ip->i_lock, MR_UPDATE) != 0);

	/*
	 * Make sure that the dquots are there. This doesn't hold
	 * the ilock across a disk read.
	 */

	error = XFS_QM_DQATTACH(mp, ip, XFS_QMOPT_ILOCKED);
	if (error)
		return XFS_ERROR(error);

retry:
	isize = ip->i_d.di_size;
	if (io->io_new_size > isize) {
		isize = io->io_new_size;
	}

	aeof = 0;
	offset_fsb = XFS_B_TO_FSBT(mp, offset);
	last_fsb = XFS_B_TO_FSB(mp, ((xfs_ufsize_t)(offset + count)));
	/*
	 * If the caller is doing a write at the end of the file,
	 * then extend the allocation (and the buffer used for the write)
	 * out to the file system's write iosize.  We clean up any extra
	 * space left over when the file is closed in xfs_inactive().
	 *
	 * We don't bother with this for sync writes, because we need
	 * to minimize the amount we write for good performance.
	 */
	if (!(ioflag & BMAP_SYNC) && ((offset + count) > ip->i_d.di_size)) {
		xfs_off_t	aligned_offset;
		unsigned int	iosize;
		xfs_fileoff_t	ioalign;

		iosize = mp->m_writeio_blocks;
		aligned_offset = XFS_WRITEIO_ALIGN(mp, (offset + count - 1));
		ioalign = XFS_B_TO_FSBT(mp, aligned_offset);
		last_fsb = ioalign + iosize;
		aeof = 1;
	}

	nimaps = XFS_WRITE_IMAPS;
	firstblock = NULLFSBLOCK;

	/*
	 * roundup the allocation request to m_dalign boundary if file size
	 * is greater that 512K and we are allocating past the allocation eof
	 */
	if (mp->m_dalign && (isize >= mp->m_dalign) && aeof) {
		int eof;
		xfs_fileoff_t new_last_fsb;
		new_last_fsb = roundup_64(last_fsb, mp->m_dalign);
		error = xfs_bmap_eof(ip, new_last_fsb, XFS_DATA_FORK, &eof);
		if (error) {
			return error;
		}
		if (eof) {
			last_fsb = new_last_fsb;
		}
	}

	error = xfs_bmapi(NULL, ip, offset_fsb,
			  (xfs_filblks_t)(last_fsb - offset_fsb),
			  XFS_BMAPI_DELAY | XFS_BMAPI_WRITE |
			  XFS_BMAPI_ENTIRE, &firstblock, 1, imap,
			  &nimaps, NULL);
	/*
	 * This can be EDQUOT, if nimaps == 0
	 */
	if (error && (error != ENOSPC)) {
		return XFS_ERROR(error);
	}
	/*
	 * If bmapi returned us nothing, and if we didn't get back EDQUOT,
	 * then we must have run out of space.
	 */

	if (nimaps == 0) {
		if (xfs_flush_space(ip, &fsynced, &ioflag))
			return XFS_ERROR(ENOSPC);

		error = 0;
		goto retry;
	}

	*ret_imap = imap[0];
	*nmaps = 1;
	return 0;
}

/*
 * Pass in a delayed allocate extent, convert it to real extents;
 * return to the caller the extent we create which maps on top of
 * the originating callers request.
 *
 * Called without a lock on the inode.
 */
int
xfs_iomap_write_allocate(
	xfs_inode_t	*ip,
	xfs_bmbt_irec_t *map,
	int		*retmap)
{
	xfs_mount_t	*mp = ip->i_mount;
	xfs_fileoff_t	offset_fsb, last_block;
	xfs_fileoff_t	end_fsb, map_start_fsb;
	xfs_fsblock_t	first_block;
	xfs_bmap_free_t	free_list;
	xfs_filblks_t	count_fsb;
	xfs_bmbt_irec_t	imap[XFS_STRAT_WRITE_IMAPS];
	xfs_trans_t	*tp;
	int		i, nimaps, committed;
	int		error = 0;
	int		nres;

	*retmap = 0;

	/*
	 * Make sure that the dquots are there.
	 */

	if ((error = XFS_QM_DQATTACH(mp, ip, 0)))
		return XFS_ERROR(error);

	offset_fsb = map->br_startoff;
	count_fsb = map->br_blockcount;
	map_start_fsb = offset_fsb;

	XFS_STATS_ADD(xfsstats.xs_xstrat_bytes, XFS_FSB_TO_B(mp, count_fsb));

	while (count_fsb != 0) {
		/*
		 * Set up a transaction with which to allocate the
		 * backing store for the file.  Do allocations in a
		 * loop until we get some space in the range we are
		 * interested in.  The other space that might be allocated
		 * is in the delayed allocation extent on which we sit
		 * but before our buffer starts.
		 */

		nimaps = 0;
		while (nimaps == 0) {
			tp = xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE);
			nres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
			error = xfs_trans_reserve(tp, nres,
					XFS_WRITE_LOG_RES(mp),
					0, XFS_TRANS_PERM_LOG_RES,
					XFS_WRITE_LOG_COUNT);

			if (error == ENOSPC) {
				error = xfs_trans_reserve(tp, 0,
						XFS_WRITE_LOG_RES(mp),
						0,
						XFS_TRANS_PERM_LOG_RES,
						XFS_WRITE_LOG_COUNT);
			}
			if (error) {
				xfs_trans_cancel(tp, 0);
				return XFS_ERROR(error);
			}
			xfs_ilock(ip, XFS_ILOCK_EXCL);
			xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
			xfs_trans_ihold(tp, ip);

			XFS_BMAP_INIT(&free_list, &first_block);

			nimaps = XFS_STRAT_WRITE_IMAPS;
			/*
			 * Ensure we don't go beyond eof - it is possible
			 * the extents changed since we did the read call,
			 * we dropped the ilock in the interim.
			 */

			end_fsb = XFS_B_TO_FSB(mp, ip->i_d.di_size);
			xfs_bmap_last_offset(NULL, ip, &last_block,
				XFS_DATA_FORK);
			last_block = XFS_FILEOFF_MAX(last_block, end_fsb);
			if ((map_start_fsb + count_fsb) > last_block) {
				count_fsb = last_block - map_start_fsb;
				if (count_fsb == 0) {
					error = EAGAIN;
					goto trans_cancel;
				}
			}

			/* Go get the actual blocks */
			error = xfs_bmapi(tp, ip, map_start_fsb, count_fsb,
					XFS_BMAPI_WRITE, &first_block, 1,
					imap, &nimaps, &free_list);

			if (error)
				goto trans_cancel;

			error = xfs_bmap_finish(&tp, &free_list,
					first_block, &committed);

			if (error)
				goto trans_cancel;

			error = xfs_trans_commit(tp,
					XFS_TRANS_RELEASE_LOG_RES, NULL);

			if (error)
				goto error0;

			xfs_iunlock(ip, XFS_ILOCK_EXCL);
		}

		/*
		 * See if we were able to allocate an extent that
		 * covers at least part of the callers request
		 */

		for (i = 0; i < nimaps; i++) {
			if ((map->br_startoff >= imap[i].br_startoff) &&
			    (map->br_startoff < (imap[i].br_startoff +
						 imap[i].br_blockcount))) {
				*map = imap[i];
				*retmap = 1;
				XFS_STATS_INC(xfsstats.xs_xstrat_quick);
				return 0;
			}
			count_fsb -= imap[i].br_blockcount;
		}

		/* So far we have not mapped the requested part of the
		 * file, just surrounding data, try again.
		 */
		nimaps--;
		offset_fsb = imap[nimaps].br_startoff +
			     imap[nimaps].br_blockcount;
		map_start_fsb = offset_fsb;
	}

trans_cancel:
	xfs_bmap_cancel(&free_list);
	xfs_trans_cancel(tp, XFS_TRANS_RELEASE_LOG_RES | XFS_TRANS_ABORT);
error0:
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	return XFS_ERROR(error);
}

int
xfs_iomap_write_unwritten(
	xfs_inode_t	*ip,
	loff_t		offset,
	size_t		count)
{
	xfs_mount_t	*mp = ip->i_mount;
	xfs_trans_t	*tp;
	xfs_fileoff_t	offset_fsb;
	xfs_filblks_t	count_fsb;
	xfs_filblks_t	numblks_fsb;
	xfs_bmbt_irec_t	imap;
	int		committed;
	int		error;
	int		nres;
	int		nimaps;
	xfs_fsblock_t	firstfsb;
	xfs_bmap_free_t	free_list;

	offset_fsb = XFS_B_TO_FSBT(mp, offset);
	count_fsb = XFS_B_TO_FSB(mp, count);

	do {
		nres = XFS_DIOSTRAT_SPACE_RES(mp, 0);

		/*
		 * set up a transaction to convert the range of extents
		 * from unwritten to real. Do allocations in a loop until
		 * we have covered the range passed in.
		 */

		tp = xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE);
		error = xfs_trans_reserve(tp, nres,
				XFS_WRITE_LOG_RES(mp), 0,
				XFS_TRANS_PERM_LOG_RES,
				XFS_WRITE_LOG_COUNT);
		if (error) {
			xfs_trans_cancel(tp, 0);
			goto error0;
		}

		xfs_ilock(ip, XFS_ILOCK_EXCL);
		xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
		xfs_trans_ihold(tp, ip);

		/*
		 * Modify the unwritten extent state of the buffer.
		 */
		XFS_BMAP_INIT(&free_list, &firstfsb);
		nimaps = 1;
		error = xfs_bmapi(tp, ip, offset_fsb, count_fsb,
				  XFS_BMAPI_WRITE, &firstfsb,
				  1, &imap, &nimaps, &free_list);
		if (error)
			goto error_on_bmapi_transaction;

		error = xfs_bmap_finish(&(tp), &(free_list),
				firstfsb, &committed);
		if (error)
			goto error_on_bmapi_transaction;

		error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES, NULL);
		xfs_iunlock(ip, XFS_ILOCK_EXCL);
		if (error)
			goto error0;

		if ((numblks_fsb = imap.br_blockcount) == 0) {
			/*
			 * The numblks_fsb value should always get
			 * smaller, otherwise the loop is stuck.
			 */
			ASSERT(imap.br_blockcount);
			break;
		}
		offset_fsb += numblks_fsb;
		count_fsb -= numblks_fsb;
	} while (count_fsb > 0);

	return 0;

error_on_bmapi_transaction:
	xfs_bmap_cancel(&free_list);
	xfs_trans_cancel(tp, (XFS_TRANS_RELEASE_LOG_RES | XFS_TRANS_ABORT));
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
error0:
	return XFS_ERROR(error);
}