[PATCH 1/6] xfs: move the dio write relocking out of xfs_ilock_for_iomap

[Christoph Hellwig <hch@lst.de>]

About half of xfs_ilock_for_iomap deals with a special case for direct
I/O writes to COW files that need to take the ilock exclusively.  Move
this code into the one callers that cares and simplify
xfs_ilock_for_iomap.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_iomap.c | 71 ++++++++++++++++++++++------------------------
 1 file changed, 34 insertions(+), 37 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 3783426739258c..b0085e5972393a 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -717,53 +717,30 @@ imap_needs_cow(
 	return true;
 }
 
+/*
+ * Extents not yet cached requires exclusive access, don't block for
+ * IOMAP_NOWAIT.
+ *
+ * This is basically an opencoded xfs_ilock_data_map_shared() call, but with
+ * support for IOMAP_NOWAIT.
+ */
 static int
 xfs_ilock_for_iomap(
 	struct xfs_inode	*ip,
 	unsigned		flags,
 	unsigned		*lockmode)
 {
-	unsigned int		mode = *lockmode;
-	bool			is_write = flags & (IOMAP_WRITE | IOMAP_ZERO);
-
-	/*
-	 * COW writes may allocate delalloc space or convert unwritten COW
-	 * extents, so we need to make sure to take the lock exclusively here.
-	 */
-	if (xfs_is_cow_inode(ip) && is_write)
-		mode = XFS_ILOCK_EXCL;
-
-	/*
-	 * Extents not yet cached requires exclusive access, don't block.  This
-	 * is an opencoded xfs_ilock_data_map_shared() call but with
-	 * non-blocking behaviour.
-	 */
-	if (xfs_need_iread_extents(&ip->i_df)) {
-		if (flags & IOMAP_NOWAIT)
-			return -EAGAIN;
-		mode = XFS_ILOCK_EXCL;
-	}
-
-relock:
 	if (flags & IOMAP_NOWAIT) {
-		if (!xfs_ilock_nowait(ip, mode))
+		if (xfs_need_iread_extents(&ip->i_df))
+			return -EAGAIN;
+		if (!xfs_ilock_nowait(ip, *lockmode))
 			return -EAGAIN;
 	} else {
-		xfs_ilock(ip, mode);
+		if (xfs_need_iread_extents(&ip->i_df))
+			*lockmode = XFS_ILOCK_EXCL;
+		xfs_ilock(ip, *lockmode);
 	}
 
-	/*
-	 * The reflink iflag could have changed since the earlier unlocked
-	 * check, so if we got ILOCK_SHARED for a write and but we're now a
-	 * reflink inode we have to switch to ILOCK_EXCL and relock.
-	 */
-	if (mode == XFS_ILOCK_SHARED && is_write && xfs_is_cow_inode(ip)) {
-		xfs_iunlock(ip, mode);
-		mode = XFS_ILOCK_EXCL;
-		goto relock;
-	}
-
-	*lockmode = mode;
 	return 0;
 }
 
@@ -801,7 +778,7 @@ xfs_direct_write_iomap_begin(
 	int			nimaps = 1, error = 0;
 	bool			shared = false;
 	u16			iomap_flags = 0;
-	unsigned int		lockmode = XFS_ILOCK_SHARED;
+	unsigned int		lockmode;
 	u64			seq;
 
 	ASSERT(flags & (IOMAP_WRITE | IOMAP_ZERO));
@@ -817,10 +794,30 @@ xfs_direct_write_iomap_begin(
 	if (offset + length > i_size_read(inode))
 		iomap_flags |= IOMAP_F_DIRTY;
 
+	/*
+	 * COW writes may allocate delalloc space or convert unwritten COW
+	 * extents, so we need to make sure to take the lock exclusively here.
+	 */
+	if (xfs_is_cow_inode(ip))
+		lockmode = XFS_ILOCK_EXCL;
+	else
+		lockmode = XFS_ILOCK_SHARED;
+
+relock:
 	error = xfs_ilock_for_iomap(ip, flags, &lockmode);
 	if (error)
 		return error;
 
+	/*
+	 * The reflink iflag could have changed since the earlier unlocked
+	 * check, check if it again and relock if needed.
+	 */
+	if (xfs_is_cow_inode(ip) && lockmode == XFS_ILOCK_SHARED) {
+		xfs_iunlock(ip, lockmode);
+		lockmode = XFS_ILOCK_EXCL;
+		goto relock;
+	}
+
 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
 			       &nimaps, 0);
 	if (error)
-- 
2.43.0