[PATCH 3.16 064/254] Btrfs: disable FUA if mounted with nobarrier

[Ben Hutchings]

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Omar Sandoval <osandov@xxxxxx>

commit 1b9e619c5bc8235cfba3dc4ced2fb0e3554a05d4 upstream.

I was seeing disk flushes still happening when I mounted a Btrfs
filesystem with nobarrier for testing. This is because we use FUA to
write out the first super block, and on devices without FUA support, the
block layer translates FUA to a flush. Even on devices supporting true
FUA, using FUA when we asked for no barriers is surprising.

Fixes: 387125fc722a8ed ("Btrfs: fix barrier flushes")
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
[bwh: Backported to 3.16:
 - I/O flag names are different, and are combined with the operation type
 - Use the do_barrier parameter instead of checking the NOBARRIER option again]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3140,6 +3140,7 @@ static int write_dev_supers(struct btrfs
 	int errors = 0;
 	u32 crc;
 	u64 bytenr;
+	int op_flags;
 
 	if (max_mirrors == 0)
 		max_mirrors = BTRFS_SUPER_MIRROR_MAX;
@@ -3204,10 +3205,10 @@ static int write_dev_supers(struct btrfs
 		 * we fua the first super.  The others we allow
 		 * to go down lazy.
 		 */
-		if (i == 0)
-			ret = btrfsic_submit_bh(WRITE_FUA, bh);
-		else
-			ret = btrfsic_submit_bh(WRITE_SYNC, bh);
+		op_flags = REQ_SYNC | REQ_NOIDLE;
+		if (i == 0 && do_barriers)
+			op_flags |= REQ_FUA;
+		ret = btrfsic_submit_bh(WRITE | op_flags, bh);
 		if (ret)
 			errors++;
 	}