iomap: return partial I/O count on error in iomap_dio_bio_actor

In case of a block device error, written parameter in iomap_end() is zero as opposed to the amount of submitted I/O. Filesystems such as btrfs need to account for the I/O in ordered extents, even if it resulted in an error. Having (incomplete) submitted bytes in written gives the filesystem the amount of data which has been submitted before the error occurred, and the filesystem code can choose how to use it.

The final returned error for iomap_dio_rw() is set by iomap_dio_complete().

Partial writes in direct I/O are considered an error. So, ->iomap_end() using written == 0 as error must be changed to written < length. In this case, ext4 is the only user.

---
 fs/ext4/inode.c      | 2 +-
 fs/iomap/direct-io.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

index e60aca791d3f..e50e7414351a 100644
@@ -3475,7 +3475,7 @@ static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
 	 * the I/O. Any blocks that may have been allocated in preparation for
 	 * the direct I/O will be reused during buffered I/O.
 	 */
-	if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written == 0)
+	if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written < length)
 		return -ENOTBLK;
 
 	return 0;

index 41c1e7c20a1f..01865db1bd09 100644
@@ -264,7 +264,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		size_t n;
 		if (dio->error) {
 			iov_iter_revert(dio->submit.iter, copied);
-			copied = ret = 0;
+			ret = 0;
 			goto out;
 		}
 

2.25.0


-- 
Goldwyn