[PATCH v3 4/6] ext4: reorder map.m_flags checks in ext4_iomap_begin()

[Matthew Bobrowski <mbobrowski@mbobrowski.org>]

For iomap direct IO write code path changes, we need to accommodate
for the case where the block mapping flags passed to ext4_map_blocks()
will result in m_flags having both EXT4_MAP_MAPPED and
EXT4_MAP_UNWRITTEN bits set. In order for the allocated unwritten
extents to be converted properly in the end_io handler, iomap->type
must be set to IOMAP_UNWRITTEN, so we need to reshuffle the
conditional statement in order to achieve this.

This change is a no-op for DAX code path as the block mapping flag
passed to ext4_map_blocks() when IS_DAX(inode) never results in
EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN being set at once.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
 fs/ext4/inode.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 761ce6286b05..efb184928e51 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3581,10 +3581,21 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
 		iomap->addr = IOMAP_NULL_ADDR;
 	} else {
-		if (map.m_flags & EXT4_MAP_MAPPED) {
-			iomap->type = IOMAP_MAPPED;
-		} else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
+		/*
+		 * Flags passed to ext4_map_blocks() for direct IO
+		 * writes can result in m_flags having both
+		 * EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In
+		 * order for allocated unwritten extents to be
+		 * converted to written extents in the end_io handler
+		 * correctly, we need to ensure that the iomap->type
+		 * is also set appropriately in that case. Thus, we
+		 * need to check whether EXT4_MAP_UNWRITTEN is set
+		 * first.
+		 */
+		if (map.m_flags & EXT4_MAP_UNWRITTEN) {
 			iomap->type = IOMAP_UNWRITTEN;
+		} else if (map.m_flags & EXT4_MAP_MAPPED) {
+			iomap->type = IOMAP_MAPPED;
 		} else {
 			WARN_ON_ONCE(1);
 			return -EIO;
-- 
2.20.1