[PATCH 2/2] xfs: rework breaking of shared extents in xfs_file_iomap_begin

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

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>
---
 fs/xfs/xfs_iomap.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)


diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a376fb2d4b94..a3043b1bcd9a 100644
--- 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			convert_now = (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,
 				convert_now);
 		if (error)
 			goto out_unlock;
@@ -1001,10 +1002,12 @@ xfs_file_iomap_begin(
 		 * previous block (if there was any) so that the higher level
 		 * write code can perform read-modify-write operations.  For
 		 * direct I/O code, which must be block aligned we need to
-		 * report the newly allocated address.
+		 * report the newly allocated address.  If the data fork has
+		 * a hole, copy the COW fork mapping to avoid allocating to
+		 * the data fork.
 		 */
-		if (!convert_now && orig.br_startblock != HOLESTARTBLOCK)
-			imap = orig;
+		if (convert_now || imap.br_startblock == HOLESTARTBLOCK)
+			imap = cmap;
 
 		end_fsb = imap.br_startoff + imap.br_blockcount;
 		length = XFS_FSB_TO_B(mp, end_fsb) - offset;