Initial import

1 files changed, 920 insertions, 0 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
new file mode 100644
index 000000000..38e633bad
--- /dev/null
+++ b/fs/xfs/xfs_iomap.c
@@ -0,0 +1,920 @@
+/*
+ * Copyright (c) 2000-2006 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_inode.h"
+#include "xfs_btree.h"
+#include "xfs_bmap_btree.h"
+#include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
+#include "xfs_error.h"
+#include "xfs_trans.h"
+#include "xfs_trans_space.h"
+#include "xfs_iomap.h"
+#include "xfs_trace.h"
+#include "xfs_icache.h"
+#include "xfs_quota.h"
+#include "xfs_dquot_item.h"
+#include "xfs_dquot.h"
+
+
+#define XFS_WRITEIO_ALIGN(mp,off)	(((off) >> mp->m_writeio_log) \
+						<< mp->m_writeio_log)
+#define XFS_WRITE_IMAPS		XFS_BMAP_MAX_NMAP
+
+STATIC int
+xfs_iomap_eof_align_last_fsb(
+	xfs_mount_t	*mp,
+	xfs_inode_t	*ip,
+	xfs_extlen_t	extsize,
+	xfs_fileoff_t	*last_fsb)
+{
+	xfs_extlen_t	align = 0;
+	int		eof, error;
+
+	if (!XFS_IS_REALTIME_INODE(ip)) {
+		/*
+		 * Round up the allocation request to a stripe unit
+		 * (m_dalign) boundary if the file size is >= stripe unit
+		 * size, and we are allocating past the allocation eof.
+		 *
+		 * If mounted with the "-o swalloc" option the alignment is
+		 * increased from the strip unit size to the stripe width.
+		 */
+		if (mp->m_swidth && (mp->m_flags & XFS_MOUNT_SWALLOC))
+			align = mp->m_swidth;
+		else if (mp->m_dalign)
+			align = mp->m_dalign;
+
+		if (align && XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, align))
+			align = 0;
+	}
+
+	/*
+	 * Always round up the allocation request to an extent boundary
+	 * (when file on a real-time subvolume or has di_extsize hint).
+	 */
+	if (extsize) {
+		if (align)
+			align = roundup_64(align, extsize);
+		else
+			align = extsize;
+	}
+
+	if (align) {
+		xfs_fileoff_t	new_last_fsb = roundup_64(*last_fsb, align);
+		error = xfs_bmap_eof(ip, new_last_fsb, XFS_DATA_FORK, &eof);
+		if (error)
+			return error;
+		if (eof)
+			*last_fsb = new_last_fsb;
+	}
+	return 0;
+}
+
+STATIC int
+xfs_alert_fsblock_zero(
+	xfs_inode_t	*ip,
+	xfs_bmbt_irec_t	*imap)
+{
+	xfs_alert_tag(ip->i_mount, XFS_PTAG_FSBLOCK_ZERO,
+			"Access to block zero in inode %llu "
+			"start_block: %llx start_off: %llx "
+			"blkcnt: %llx extent-state: %x",
+		(unsigned long long)ip->i_ino,
+		(unsigned long long)imap->br_startblock,
+		(unsigned long long)imap->br_startoff,
+		(unsigned long long)imap->br_blockcount,
+		imap->br_state);
+	return -EFSCORRUPTED;
+}
+
+int
+xfs_iomap_write_direct(
+	xfs_inode_t	*ip,
+	xfs_off_t	offset,
+	size_t		count,
+	xfs_bmbt_irec_t *imap,
+	int		nmaps)
+{
+	xfs_mount_t	*mp = ip->i_mount;
+	xfs_fileoff_t	offset_fsb;
+	xfs_fileoff_t	last_fsb;
+	xfs_filblks_t	count_fsb, resaligned;
+	xfs_fsblock_t	firstfsb;
+	xfs_extlen_t	extsz, temp;
+	int		nimaps;
+	int		quota_flag;
+	int		rt;
+	xfs_trans_t	*tp;
+	xfs_bmap_free_t free_list;
+	uint		qblocks, resblks, resrtextents;
+	int		committed;
+	int		error;
+
+	error = xfs_qm_dqattach(ip, 0);
+	if (error)
+		return error;
+
+	rt = XFS_IS_REALTIME_INODE(ip);
+	extsz = xfs_get_extsz_hint(ip);
+
+	offset_fsb = XFS_B_TO_FSBT(mp, offset);
+	last_fsb = XFS_B_TO_FSB(mp, ((xfs_ufsize_t)(offset + count)));
+	if ((offset + count) > XFS_ISIZE(ip)) {
+		error = xfs_iomap_eof_align_last_fsb(mp, ip, extsz, &last_fsb);
+		if (error)
+			return error;
+	} else {
+		if (nmaps && (imap->br_startblock == HOLESTARTBLOCK))
+			last_fsb = MIN(last_fsb, (xfs_fileoff_t)
+					imap->br_blockcount +
+					imap->br_startoff);
+	}
+	count_fsb = last_fsb - offset_fsb;
+	ASSERT(count_fsb > 0);
+
+	resaligned = count_fsb;
+	if (unlikely(extsz)) {
+		if ((temp = do_mod(offset_fsb, extsz)))
+			resaligned += temp;
+		if ((temp = do_mod(resaligned, extsz)))
+			resaligned += extsz - temp;
+	}
+
+	if (unlikely(rt)) {
+		resrtextents = qblocks = resaligned;
+		resrtextents /= mp->m_sb.sb_rextsize;
+		resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0);
+		quota_flag = XFS_QMOPT_RES_RTBLKS;
+	} else {
+		resrtextents = 0;
+		resblks = qblocks = XFS_DIOSTRAT_SPACE_RES(mp, resaligned);
+		quota_flag = XFS_QMOPT_RES_REGBLKS;
+	}
+
+	/*
+	 * Allocate and setup the transaction
+	 */
+	tp = xfs_trans_alloc(mp, XFS_TRANS_DIOSTRAT);
+	error = xfs_trans_reserve(tp, &M_RES(mp)->tr_write,
+				  resblks, resrtextents);
+	/*
+	 * Check for running out of space, note: need lock to return
+	 */
+	if (error) {
+		xfs_trans_cancel(tp, 0);
+		return error;
+	}
+
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+
+	error = xfs_trans_reserve_quota_nblks(tp, ip, qblocks, 0, quota_flag);
+	if (error)
+		goto out_trans_cancel;
+
+	xfs_trans_ijoin(tp, ip, 0);
+
+	/*
+	 * From this point onwards we overwrite the imap pointer that the
+	 * caller gave to us.
+	 */
+	xfs_bmap_init(&free_list, &firstfsb);
+	nimaps = 1;
+	error = xfs_bmapi_write(tp, ip, offset_fsb, count_fsb,
+				XFS_BMAPI_PREALLOC, &firstfsb, 0,
+				imap, &nimaps, &free_list);
+	if (error)
+		goto out_bmap_cancel;
+
+	/*
+	 * Complete the transaction
+	 */
+	error = xfs_bmap_finish(&tp, &free_list, &committed);
+	if (error)
+		goto out_bmap_cancel;
+	error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
+	if (error)
+		goto out_unlock;
+
+	/*
+	 * Copy any maps to caller's array and return any error.
+	 */
+	if (nimaps == 0) {
+		error = -ENOSPC;
+		goto out_unlock;
+	}
+
+	if (!(imap->br_startblock || XFS_IS_REALTIME_INODE(ip)))
+		error = xfs_alert_fsblock_zero(ip, imap);
+
+out_unlock:
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+
+out_bmap_cancel:
+	xfs_bmap_cancel(&free_list);
+	xfs_trans_unreserve_quota_nblks(tp, ip, (long)qblocks, 0, quota_flag);
+out_trans_cancel:
+	xfs_trans_cancel(tp, XFS_TRANS_RELEASE_LOG_RES | XFS_TRANS_ABORT);
+	goto out_unlock;
+}
+
+/*
+ * If the caller is doing a write at the end of the file, then extend the
+ * allocation out to the file system's write iosize.  We clean up any extra
+ * space left over when the file is closed in xfs_inactive().
+ *
+ * If we find we already have delalloc preallocation beyond EOF, don't do more
+ * preallocation as it it not needed.
+ */
+STATIC int
+xfs_iomap_eof_want_preallocate(
+	xfs_mount_t	*mp,
+	xfs_inode_t	*ip,
+	xfs_off_t	offset,
+	size_t		count,
+	xfs_bmbt_irec_t *imap,
+	int		nimaps,
+	int		*prealloc)
+{
+	xfs_fileoff_t   start_fsb;
+	xfs_filblks_t   count_fsb;
+	int		n, error, imaps;
+	int		found_delalloc = 0;
+
+	*prealloc = 0;
+	if (offset + count <= XFS_ISIZE(ip))
+		return 0;
+
+	/*
+	 * If the file is smaller than the minimum prealloc and we are using
+	 * dynamic preallocation, don't do any preallocation at all as it is
+	 * likely this is the only write to the file that is going to be done.
+	 */
+	if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE) &&
+	    XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_writeio_blocks))
+		return 0;
+
+	/*
+	 * If there are any real blocks past eof, then don't
+	 * do any speculative allocation.
+	 */
+	start_fsb = XFS_B_TO_FSBT(mp, ((xfs_ufsize_t)(offset + count - 1)));
+	count_fsb = XFS_B_TO_FSB(mp, mp->m_super->s_maxbytes);
+	while (count_fsb > 0) {
+		imaps = nimaps;
+		error = xfs_bmapi_read(ip, start_fsb, count_fsb, imap, &imaps,
+				       0);
+		if (error)
+			return error;
+		for (n = 0; n < imaps; n++) {
+			if ((imap[n].br_startblock != HOLESTARTBLOCK) &&
+			    (imap[n].br_startblock != DELAYSTARTBLOCK))
+				return 0;
+			start_fsb += imap[n].br_blockcount;
+			count_fsb -= imap[n].br_blockcount;
+
+			if (imap[n].br_startblock == DELAYSTARTBLOCK)
+				found_delalloc = 1;
+		}
+	}
+	if (!found_delalloc)
+		*prealloc = 1;
+	return 0;
+}
+
+/*
+ * Determine the initial size of the preallocation. We are beyond the current
+ * EOF here, but we need to take into account whether this is a sparse write or
+ * an extending write when determining the preallocation size.  Hence we need to
+ * look up the extent that ends at the current write offset and use the result
+ * to determine the preallocation size.
+ *
+ * If the extent is a hole, then preallocation is essentially disabled.
+ * Otherwise we take the size of the preceeding data extent as the basis for the
+ * preallocation size. If the size of the extent is greater than half the
+ * maximum extent length, then use the current offset as the basis. This ensures
+ * that for large files the preallocation size always extends to MAXEXTLEN
+ * rather than falling short due to things like stripe unit/width alignment of
+ * real extents.
+ */
+STATIC xfs_fsblock_t
+xfs_iomap_eof_prealloc_initial_size(
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	xfs_off_t		offset,
+	xfs_bmbt_irec_t		*imap,
+	int			nimaps)
+{
+	xfs_fileoff_t   start_fsb;
+	int		imaps = 1;
+	int		error;
+
+	ASSERT(nimaps >= imaps);
+
+	/* if we are using a specific prealloc size, return now */
+	if (mp->m_flags & XFS_MOUNT_DFLT_IOSIZE)
+		return 0;
+
+	/* If the file is small, then use the minimum prealloc */
+	if (XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_dalign))
+		return 0;
+
+	/*
+	 * As we write multiple pages, the offset will always align to the
+	 * start of a page and hence point to a hole at EOF. i.e. if the size is
+	 * 4096 bytes, we only have one block at FSB 0, but XFS_B_TO_FSB(4096)
+	 * will return FSB 1. Hence if there are blocks in the file, we want to
+	 * point to the block prior to the EOF block and not the hole that maps
+	 * directly at @offset.
+	 */
+	start_fsb = XFS_B_TO_FSB(mp, offset);
+	if (start_fsb)
+		start_fsb--;
+	error = xfs_bmapi_read(ip, start_fsb, 1, imap, &imaps, XFS_BMAPI_ENTIRE);
+	if (error)
+		return 0;
+
+	ASSERT(imaps == 1);
+	if (imap[0].br_startblock == HOLESTARTBLOCK)
+		return 0;
+	if (imap[0].br_blockcount <= (MAXEXTLEN >> 1))
+		return imap[0].br_blockcount << 1;
+	return XFS_B_TO_FSB(mp, offset);
+}
+
+STATIC bool
+xfs_quota_need_throttle(
+	struct xfs_inode *ip,
+	int type,
+	xfs_fsblock_t alloc_blocks)
+{
+	struct xfs_dquot *dq = xfs_inode_dquot(ip, type);
+
+	if (!dq || !xfs_this_quota_on(ip->i_mount, type))
+		return false;
+
+	/* no hi watermark, no throttle */
+	if (!dq->q_prealloc_hi_wmark)
+		return false;
+
+	/* under the lo watermark, no throttle */
+	if (dq->q_res_bcount + alloc_blocks < dq->q_prealloc_lo_wmark)
+		return false;
+
+	return true;
+}
+
+STATIC void
+xfs_quota_calc_throttle(
+	struct xfs_inode *ip,
+	int type,
+	xfs_fsblock_t *qblocks,
+	int *qshift,
+	int64_t	*qfreesp)
+{
+	int64_t freesp;
+	int shift = 0;
+	struct xfs_dquot *dq = xfs_inode_dquot(ip, type);
+
+	/* no dq, or over hi wmark, squash the prealloc completely */
+	if (!dq || dq->q_res_bcount >= dq->q_prealloc_hi_wmark) {
+		*qblocks = 0;
+		*qfreesp = 0;
+		return;
+	}
+
+	freesp = dq->q_prealloc_hi_wmark - dq->q_res_bcount;
+	if (freesp < dq->q_low_space[XFS_QLOWSP_5_PCNT]) {
+		shift = 2;
+		if (freesp < dq->q_low_space[XFS_QLOWSP_3_PCNT])
+			shift += 2;
+		if (freesp < dq->q_low_space[XFS_QLOWSP_1_PCNT])
+			shift += 2;
+	}
+
+	if (freesp < *qfreesp)
+		*qfreesp = freesp;
+
+	/* only overwrite the throttle values if we are more aggressive */
+	if ((freesp >> shift) < (*qblocks >> *qshift)) {
+		*qblocks = freesp;
+		*qshift = shift;
+	}
+}
+
+/*
+ * If we don't have a user specified preallocation size, dynamically increase
+ * the preallocation size as the size of the file grows. Cap the maximum size
+ * at a single extent or less if the filesystem is near full. The closer the
+ * filesystem is to full, the smaller the maximum prealocation.
+ */
+STATIC xfs_fsblock_t
+xfs_iomap_prealloc_size(
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	xfs_off_t		offset,
+	struct xfs_bmbt_irec	*imap,
+	int			nimaps)
+{
+	xfs_fsblock_t		alloc_blocks = 0;
+	int			shift = 0;
+	int64_t			freesp;
+	xfs_fsblock_t		qblocks;
+	int			qshift = 0;
+
+	alloc_blocks = xfs_iomap_eof_prealloc_initial_size(mp, ip, offset,
+							   imap, nimaps);
+	if (!alloc_blocks)
+		goto check_writeio;
+	qblocks = alloc_blocks;
+
+	/*
+	 * MAXEXTLEN is not a power of two value but we round the prealloc down
+	 * to the nearest power of two value after throttling. To prevent the
+	 * round down from unconditionally reducing the maximum supported prealloc
+	 * size, we round up first, apply appropriate throttling, round down and
+	 * cap the value to MAXEXTLEN.
+	 */
+	alloc_blocks = XFS_FILEOFF_MIN(roundup_pow_of_two(MAXEXTLEN),
+				       alloc_blocks);
+
+	freesp = percpu_counter_read_positive(&mp->m_fdblocks);
+	if (freesp < mp->m_low_space[XFS_LOWSP_5_PCNT]) {
+		shift = 2;
+		if (freesp < mp->m_low_space[XFS_LOWSP_4_PCNT])
+			shift++;
+		if (freesp < mp->m_low_space[XFS_LOWSP_3_PCNT])
+			shift++;
+		if (freesp < mp->m_low_space[XFS_LOWSP_2_PCNT])
+			shift++;
+		if (freesp < mp->m_low_space[XFS_LOWSP_1_PCNT])
+			shift++;
+	}
+
+	/*
+	 * Check each quota to cap the prealloc size, provide a shift value to
+	 * throttle with and adjust amount of available space.
+	 */
+	if (xfs_quota_need_throttle(ip, XFS_DQ_USER, alloc_blocks))
+		xfs_quota_calc_throttle(ip, XFS_DQ_USER, &qblocks, &qshift,
+					&freesp);
+	if (xfs_quota_need_throttle(ip, XFS_DQ_GROUP, alloc_blocks))
+		xfs_quota_calc_throttle(ip, XFS_DQ_GROUP, &qblocks, &qshift,
+					&freesp);
+	if (xfs_quota_need_throttle(ip, XFS_DQ_PROJ, alloc_blocks))
+		xfs_quota_calc_throttle(ip, XFS_DQ_PROJ, &qblocks, &qshift,
+					&freesp);
+
+	/*
+	 * The final prealloc size is set to the minimum of free space available
+	 * in each of the quotas and the overall filesystem.
+	 *
+	 * The shift throttle value is set to the maximum value as determined by
+	 * the global low free space values and per-quota low free space values.
+	 */
+	alloc_blocks = MIN(alloc_blocks, qblocks);
+	shift = MAX(shift, qshift);
+
+	if (shift)
+		alloc_blocks >>= shift;
+	/*
+	 * rounddown_pow_of_two() returns an undefined result if we pass in
+	 * alloc_blocks = 0.
+	 */
+	if (alloc_blocks)
+		alloc_blocks = rounddown_pow_of_two(alloc_blocks);
+	if (alloc_blocks > MAXEXTLEN)
+		alloc_blocks = MAXEXTLEN;
+
+	/*
+	 * If we are still trying to allocate more space than is
+	 * available, squash the prealloc hard. This can happen if we
+	 * have a large file on a small filesystem and the above
+	 * lowspace thresholds are smaller than MAXEXTLEN.
+	 */
+	while (alloc_blocks && alloc_blocks >= freesp)
+		alloc_blocks >>= 4;
+
+check_writeio:
+	if (alloc_blocks < mp->m_writeio_blocks)
+		alloc_blocks = mp->m_writeio_blocks;
+
+	trace_xfs_iomap_prealloc_size(ip, alloc_blocks, shift,
+				      mp->m_writeio_blocks);
+
+	return alloc_blocks;
+}
+
+int
+xfs_iomap_write_delay(
+	xfs_inode_t	*ip,
+	xfs_off_t	offset,
+	size_t		count,
+	xfs_bmbt_irec_t *ret_imap)
+{
+	xfs_mount_t	*mp = ip->i_mount;
+	xfs_fileoff_t	offset_fsb;
+	xfs_fileoff_t	last_fsb;
+	xfs_off_t	aligned_offset;
+	xfs_fileoff_t	ioalign;
+	xfs_extlen_t	extsz;
+	int		nimaps;
+	xfs_bmbt_irec_t imap[XFS_WRITE_IMAPS];
+	int		prealloc;
+	int		error;
+
+	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
+
+	/*
+	 * Make sure that the dquots are there. This doesn't hold
+	 * the ilock across a disk read.
+	 */
+	error = xfs_qm_dqattach_locked(ip, 0);
+	if (error)
+		return error;
+
+	extsz = xfs_get_extsz_hint(ip);
+	offset_fsb = XFS_B_TO_FSBT(mp, offset);
+
+	error = xfs_iomap_eof_want_preallocate(mp, ip, offset, count,
+				imap, XFS_WRITE_IMAPS, &prealloc);
+	if (error)
+		return error;
+
+retry:
+	if (prealloc) {
+		xfs_fsblock_t	alloc_blocks;
+
+		alloc_blocks = xfs_iomap_prealloc_size(mp, ip, offset, imap,
+						       XFS_WRITE_IMAPS);
+
+		aligned_offset = XFS_WRITEIO_ALIGN(mp, (offset + count - 1));
+		ioalign = XFS_B_TO_FSBT(mp, aligned_offset);
+		last_fsb = ioalign + alloc_blocks;
+	} else {
+		last_fsb = XFS_B_TO_FSB(mp, ((xfs_ufsize_t)(offset + count)));
+	}
+
+	if (prealloc || extsz) {
+		error = xfs_iomap_eof_align_last_fsb(mp, ip, extsz, &last_fsb);
+		if (error)
+			return error;
+	}
+
+	/*
+	 * Make sure preallocation does not create extents beyond the range we
+	 * actually support in this filesystem.
+	 */
+	if (last_fsb > XFS_B_TO_FSB(mp, mp->m_super->s_maxbytes))
+		last_fsb = XFS_B_TO_FSB(mp, mp->m_super->s_maxbytes);
+
+	ASSERT(last_fsb > offset_fsb);
+
+	nimaps = XFS_WRITE_IMAPS;
+	error = xfs_bmapi_delay(ip, offset_fsb, last_fsb - offset_fsb,
+				imap, &nimaps, XFS_BMAPI_ENTIRE);
+	switch (error) {
+	case 0:
+	case -ENOSPC:
+	case -EDQUOT:
+		break;
+	default:
+		return error;
+	}
+
+	/*
+	 * If bmapi returned us nothing, we got either ENOSPC or EDQUOT. Retry
+	 * without EOF preallocation.
+	 */
+	if (nimaps == 0) {
+		trace_xfs_delalloc_enospc(ip, offset, count);
+		if (prealloc) {
+			prealloc = 0;
+			error = 0;
+			goto retry;
+		}
+		return error ? error : -ENOSPC;
+	}
+
+	if (!(imap[0].br_startblock || XFS_IS_REALTIME_INODE(ip)))
+		return xfs_alert_fsblock_zero(ip, &imap[0]);
+
+	/*
+	 * Tag the inode as speculatively preallocated so we can reclaim this
+	 * space on demand, if necessary.
+	 */
+	if (prealloc)
+		xfs_inode_set_eofblocks_tag(ip);
+
+	*ret_imap = imap[0];
+	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.
+ *
+ * We no longer bother to look at the incoming map - all we have to
+ * guarantee is that whatever we allocate fills the required range.
+ */
+int
+xfs_iomap_write_allocate(
+	xfs_inode_t	*ip,
+	xfs_off_t	offset,
+	xfs_bmbt_irec_t *imap)
+{
+	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_trans_t	*tp;
+	int		nimaps, committed;
+	int		error = 0;
+	int		nres;
+
+	/*
+	 * Make sure that the dquots are there.
+	 */
+	error = xfs_qm_dqattach(ip, 0);
+	if (error)
+		return error;
+
+	offset_fsb = XFS_B_TO_FSBT(mp, offset);
+	count_fsb = imap->br_blockcount;
+	map_start_fsb = imap->br_startoff;
+
+	XFS_STATS_ADD(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);
+			tp->t_flags |= XFS_TRANS_RESERVE;
+			nres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
+			error = xfs_trans_reserve(tp, &M_RES(mp)->tr_write,
+						  nres, 0);
+			if (error) {
+				xfs_trans_cancel(tp, 0);
+				return error;
+			}
+			xfs_ilock(ip, XFS_ILOCK_EXCL);
+			xfs_trans_ijoin(tp, ip, 0);
+
+			xfs_bmap_init(&free_list, &first_block);
+
+			/*
+			 * it is possible that the extents have changed since
+			 * we did the read call as we dropped the ilock for a
+			 * while. We have to be careful about truncates or hole
+			 * punchs here - we are not allowed to allocate
+			 * non-delalloc blocks here.
+			 *
+			 * The only protection against truncation is the pages
+			 * for the range we are being asked to convert are
+			 * locked and hence a truncate will block on them
+			 * first.
+			 *
+			 * As a result, if we go beyond the range we really
+			 * need and hit an delalloc extent boundary followed by
+			 * a hole while we have excess blocks in the map, we
+			 * will fill the hole incorrectly and overrun the
+			 * transaction reservation.
+			 *
+			 * Using a single map prevents this as we are forced to
+			 * check each map we look for overlap with the desired
+			 * range and abort as soon as we find it. Also, given
+			 * that we only return a single map, having one beyond
+			 * what we can return is probably a bit silly.
+			 *
+			 * We also need to check that we don't go beyond EOF;
+			 * this is a truncate optimisation as a truncate sets
+			 * the new file size before block on the pages we
+			 * currently have locked under writeback. Because they
+			 * are about to be tossed, we don't need to write them
+			 * back....
+			 */
+			nimaps = 1;
+			end_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
+			error = xfs_bmap_last_offset(ip, &last_block,
+							XFS_DATA_FORK);
+			if (error)
+				goto trans_cancel;
+
+			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;
+				}
+			}
+
+			/*
+			 * From this point onwards we overwrite the imap
+			 * pointer that the caller gave to us.
+			 */
+			error = xfs_bmapi_write(tp, ip, map_start_fsb,
+						count_fsb, 0,
+						&first_block, 1,
+						imap, &nimaps, &free_list);
+			if (error)
+				goto trans_cancel;
+
+			error = xfs_bmap_finish(&tp, &free_list, &committed);
+			if (error)
+				goto trans_cancel;
+
+			error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
+			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
+		 */
+		if (!(imap->br_startblock || XFS_IS_REALTIME_INODE(ip)))
+			return xfs_alert_fsblock_zero(ip, imap);
+
+		if ((offset_fsb >= imap->br_startoff) &&
+		    (offset_fsb < (imap->br_startoff +
+				   imap->br_blockcount))) {
+			XFS_STATS_INC(xs_xstrat_quick);
+			return 0;
+		}
+
+		/*
+		 * So far we have not mapped the requested part of the
+		 * file, just surrounding data, try again.
+		 */
+		count_fsb -= imap->br_blockcount;
+		map_start_fsb = imap->br_startoff + imap->br_blockcount;
+	}
+
+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 error;
+}
+
+int
+xfs_iomap_write_unwritten(
+	xfs_inode_t	*ip,
+	xfs_off_t	offset,
+	xfs_off_t	count)
+{
+	xfs_mount_t	*mp = ip->i_mount;
+	xfs_fileoff_t	offset_fsb;
+	xfs_filblks_t	count_fsb;
+	xfs_filblks_t	numblks_fsb;
+	xfs_fsblock_t	firstfsb;
+	int		nimaps;
+	xfs_trans_t	*tp;
+	xfs_bmbt_irec_t imap;
+	xfs_bmap_free_t free_list;
+	xfs_fsize_t	i_size;
+	uint		resblks;
+	int		committed;
+	int		error;
+
+	trace_xfs_unwritten_convert(ip, offset, count);
+
+	offset_fsb = XFS_B_TO_FSBT(mp, offset);
+	count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
+	count_fsb = (xfs_filblks_t)(count_fsb - offset_fsb);
+
+	/*
+	 * Reserve enough blocks in this transaction for two complete extent
+	 * btree splits.  We may be converting the middle part of an unwritten
+	 * extent and in this case we will insert two new extents in the btree
+	 * each of which could cause a full split.
+	 *
+	 * This reservation amount will be used in the first call to
+	 * xfs_bmbt_split() to select an AG with enough space to satisfy the
+	 * rest of the operation.
+	 */
+	resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0) << 1;
+
+	do {
+		/*
+		 * 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.
+		 *
+		 * Note that we open code the transaction allocation here
+		 * to pass KM_NOFS--we can't risk to recursing back into
+		 * the filesystem here as we might be asked to write out
+		 * the same inode that we complete here and might deadlock
+		 * on the iolock.
+		 */
+		sb_start_intwrite(mp->m_super);
+		tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE, KM_NOFS);
+		tp->t_flags |= XFS_TRANS_RESERVE | XFS_TRANS_FREEZE_PROT;
+		error = xfs_trans_reserve(tp, &M_RES(mp)->tr_write,
+					  resblks, 0);
+		if (error) {
+			xfs_trans_cancel(tp, 0);
+			return error;
+		}
+
+		xfs_ilock(ip, XFS_ILOCK_EXCL);
+		xfs_trans_ijoin(tp, ip, 0);
+
+		/*
+		 * Modify the unwritten extent state of the buffer.
+		 */
+		xfs_bmap_init(&free_list, &firstfsb);
+		nimaps = 1;
+		error = xfs_bmapi_write(tp, ip, offset_fsb, count_fsb,
+				  XFS_BMAPI_CONVERT, &firstfsb,
+				  1, &imap, &nimaps, &free_list);
+		if (error)
+			goto error_on_bmapi_transaction;
+
+		/*
+		 * Log the updated inode size as we go.  We have to be careful
+		 * to only log it up to the actual write offset if it is
+		 * halfway into a block.
+		 */
+		i_size = XFS_FSB_TO_B(mp, offset_fsb + count_fsb);
+		if (i_size > offset + count)
+			i_size = offset + count;
+
+		i_size = xfs_new_eof(ip, i_size);
+		if (i_size) {
+			ip->i_d.di_size = i_size;
+			xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
+		}
+
+		error = xfs_bmap_finish(&tp, &free_list, &committed);
+		if (error)
+			goto error_on_bmapi_transaction;
+
+		error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
+		xfs_iunlock(ip, XFS_ILOCK_EXCL);
+		if (error)
+			return error;
+
+		if (!(imap.br_startblock || XFS_IS_REALTIME_INODE(ip)))
+			return xfs_alert_fsblock_zero(ip, &imap);
+
+		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);
+	return error;
+}