xfs: rework breaking of shared extents in xfs_file_iomap_begin

Rework the data flow in xfs_file_iomap_begin where we decide if we have
to break shared extents.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index fa6621448d5e768841e65dd9ac107d7e58291dbc..63d323916bba9e42dc3f37d81359b16a6821784b 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -982,7 +982,7 @@ xfs_file_iomap_begin(
         * been done up front, so we don't need to do them here.
         */
        if (xfs_is_cow_inode(ip)) {
-               struct xfs_bmbt_irec    orig = imap;
+               struct xfs_bmbt_irec    cmap;
                bool                    directio = (flags & IOMAP_DIRECT);
 
                /* if zeroing doesn't need COW allocation, then we are done. */
@@ -991,7 +991,8 @@ xfs_file_iomap_begin(
                        goto out_found;
 
                /* may drop and re-acquire the ilock */
-               error = xfs_reflink_allocate_cow(ip, &imap, &shared, &lockmode,
+               cmap = imap;
+               error = xfs_reflink_allocate_cow(ip, &cmap, &shared, &lockmode,
                                directio);
                if (error)
                        goto out_unlock;
@@ -1002,10 +1003,11 @@ xfs_file_iomap_begin(
                 * write code can perform read-modify-write operations; we
                 * won't need the CoW fork mapping until writeback.  For direct
                 * I/O, which must be block aligned, we need to report the
-                * newly allocated address.
+                * newly allocated address.  If the data fork has a hole, copy
+                * the COW fork mapping to avoid allocating to the data fork.
                 */
-               if (!directio && orig.br_startblock != HOLESTARTBLOCK)
-                       imap = orig;
+               if (directio || imap.br_startblock == HOLESTARTBLOCK)
+                       imap = cmap;
 
                end_fsb = imap.br_startoff + imap.br_blockcount;
                length = XFS_FSB_TO_B(mp, end_fsb) - offset;