[PATCH] ext4: Set barrier=0 when block device does not advertiseflush support

[Darrick J. Wong]

If the user tries to enable write flushes with "barrier=1" and the underlying
block device does not support flushes, print a message and set barrier=0.

Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---

 fs/ext4/super.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e32195d..098dcf0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3124,6 +3124,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			   &journal_ioprio, NULL, 0))
 		goto failed_mount;
 
+	/* Catch barrier=1 and no flush support */
+	if (test_opt(sb, BARRIER) &&
+		     !(sb->s_bdev->bd_disk->queue->flush_flags & REQ_FLUSH)) {
+		ext4_msg(sb, KERN_WARNING, "flush not supported; disabling.");
+		clear_opt(sbi->s_mount_opt, BARRIER);
+	}
+
 	sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
 		(test_opt(sb, POSIX_ACL) ? MS_POSIXACL : 0);
 
@@ -4198,6 +4205,13 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 		goto restore_opts;
 	}
 
+	/* Catch barrier=1 and no flush support */
+	if (test_opt(sb, BARRIER) &&
+		     !(sb->s_bdev->bd_disk->queue->flush_flags & REQ_FLUSH)) {
+		ext4_msg(sb, KERN_WARNING, "flush not supported; disabling.");
+		clear_opt(sbi->s_mount_opt, BARRIER);
+	}
+
 	if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
 		ext4_abort(sb, "Abort forced by user");
 
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