[PATCH v4 7/8] ext4: reorder map.m_flags checks in ext4_set_iomap()

[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>
---
 fs/ext4/inode.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e133dda55063..63ad23ae05b8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3420,10 +3420,20 @@ static int ext4_set_iomap(struct inode *inode, struct iomap *iomap, u16 type,
 		iomap->type = type;
 		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 I/O
+		 * writes can result in map->m_flags having both
+		 * EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In
+		 * order for allocated extents to be converted to
+		 * written extents in the ->end_io handler correctly,
+		 * we need to ensure that the iomap->type is set
+		 * approprately. 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