[PATCH 06/11] xfs: don't use delalloc extents for COW on files with extsize hints

[Christoph Hellwig <hch@lst.de>]

While using delalloc for extsize hints is generally a good idea, the
current code that does so only for COW doesn't help us much and creates
a lot of special cases.  Switch it to use real allocations like we
do for direct I/O.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_iomap.c   | 28 +++++++++++++++++-----------
 fs/xfs/xfs_reflink.c | 10 +++++++++-
 fs/xfs/xfs_reflink.h |  3 ++-
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 9f1fd224bb06..d851abac16a9 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1039,22 +1039,28 @@ xfs_file_iomap_begin(
 	 * been done up front, so we don't need to do them here.
 	 */
 	if (xfs_is_reflink_inode(ip)) {
+		struct xfs_bmbt_irec	orig = imap;
+
 		/* if zeroing doesn't need COW allocation, then we are done. */
 		if ((flags & IOMAP_ZERO) &&
 		    !needs_cow_for_zeroing(&imap, nimaps))
 			goto out_found;
 
-		if (flags & IOMAP_DIRECT) {
-			/* may drop and re-acquire the ilock */
-			error = xfs_reflink_allocate_cow(ip, &imap, &shared,
-					&lockmode);
-			if (error)
-				goto out_unlock;
-		} else {
-			error = xfs_reflink_reserve_cow(ip, &imap);
-			if (error)
-				goto out_unlock;
-		}
+		error = xfs_reflink_allocate_cow(ip, &imap, &shared, &lockmode,
+						 flags);
+		if (error)
+			goto out_unlock;
+
+		/*
+		 * For buffered writes we need to report the address of the
+		 * 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.
+		 */
+		if (!(flags & IOMAP_DIRECT) &&
+		    orig.br_startblock != HOLESTARTBLOCK)
+			imap = orig;
 
 		end_fsb = imap.br_startoff + imap.br_blockcount;
 		length = XFS_FSB_TO_B(mp, end_fsb) - offset;
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 2babc2cbe103..8a5353daf9ab 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -397,7 +397,8 @@ xfs_reflink_allocate_cow(
 	struct xfs_inode	*ip,
 	struct xfs_bmbt_irec	*imap,
 	bool			*shared,
-	uint			*lockmode)
+	uint			*lockmode,
+	unsigned		iomap_flags)
 {
 	struct xfs_mount	*mp = ip->i_mount;
 	xfs_fileoff_t		offset_fsb = imap->br_startoff;
@@ -471,6 +472,13 @@ xfs_reflink_allocate_cow(
 	if (nimaps == 0)
 		return -ENOSPC;
 convert:
+	/*
+	 * COW fork extents are supposed to remain unwritten until we're ready
+	 * to initiate a disk write.  For direct I/O we are going to write the
+	 * data and need the conversion, but for buffered writes we're done.
+	 */
+	if (!(iomap_flags & IOMAP_DIRECT))
+		return 0;
 	return xfs_reflink_convert_cow_extent(ip, imap, offset_fsb, count_fsb);
 
 out_unreserve:
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index 6d73daef1f13..70d68a1a9b49 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -15,7 +15,8 @@ extern int xfs_reflink_trim_around_shared(struct xfs_inode *ip,
 extern int xfs_reflink_reserve_cow(struct xfs_inode *ip,
 		struct xfs_bmbt_irec *imap);
 extern int xfs_reflink_allocate_cow(struct xfs_inode *ip,
-		struct xfs_bmbt_irec *imap, bool *shared, uint *lockmode);
+		struct xfs_bmbt_irec *imap, bool *shared, uint *lockmode,
+		unsigned iomap_flags);
 extern int xfs_reflink_convert_cow(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
 
-- 
2.20.1