text: /*
   * Copyright (c) 2000-2006 Silicon Graphics, Inc.
   * All Rights Reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it would be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
   */
  #include "xfs.h"
  #include "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;
  	int		lockmode;
  	int		bmapi_flags = XFS_BMAPI_PREALLOC;
  
  	rt = XFS_IS_REALTIME_INODE(ip);
  	extsz = xfs_get_extsz_hint(ip);
  	lockmode = XFS_ILOCK_SHARED;	/* locked by caller */
  
  	ASSERT(xfs_isilocked(ip, lockmode));
  
  	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)) {
  		/*
  		 * Assert that the in-core extent list is present since this can
  		 * call xfs_iread_extents() and we only have the ilock shared.
  		 * This should be safe because the lock was held around a bmapi
  		 * call in the caller and we only need it to access the in-core
  		 * list.
  		 */
  		ASSERT(XFS_IFORK_PTR(ip, XFS_DATA_FORK)->if_flags &
  								XFS_IFEXTENTS);
  		error = xfs_iomap_eof_align_last_fsb(mp, ip, extsz, &last_fsb);
  		if (error)
  			goto out_unlock;
  	} 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;
  	}
  
  	/*
  	 * Drop the shared lock acquired by the caller, attach the dquot if
  	 * necessary and move on to transaction setup.
  	 */
  	xfs_iunlock(ip, lockmode);
  	error = xfs_qm_dqattach(ip, 0);
  	if (error)
  		return error;
  
  	/*
  	 * Allocate and setup the transaction
  	 */
  	tp = xfs_trans_alloc(mp, XFS_TRANS_DIOSTRAT);
  
  	/*
  	 * For DAX, we do not allocate unwritten extents, but instead we zero
  	 * the block before we commit the transaction.  Ideally we'd like to do
  	 * this outside the transaction context, but if we commit and then crash
  	 * we may not have zeroed the blocks and this will be exposed on
  	 * recovery of the allocation. Hence we must zero before commit.
  	 * Further, if we are mapping unwritten extents here, we need to zero
  	 * and convert them to written so that we don't need an unwritten extent
  	 * callback for DAX. This also means that we need to be able to dip into
  	 * the reserve block pool if there is no space left but we need to do
  	 * unwritten extent conversion.
  	 */
  	if (IS_DAX(VFS_I(ip))) {
  		bmapi_flags = XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO;
  		tp->t_flags |= XFS_TRANS_RESERVE;
  	}
  	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);
  		return error;
  	}
  
  	lockmode = XFS_ILOCK_EXCL;
  	xfs_ilock(ip, lockmode);
  
  	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,
  				bmapi_flags, &firstfsb, resblks, 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);
  	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, lockmode);
  	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);
  	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(mp, 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);
  				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,
  						nres, 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);
  			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(mp, 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);
  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);
  			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, resblks,
  					&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_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_iunlock(ip, XFS_ILOCK_EXCL);
  	return error;
  }
  