Mark a superblock that is for for an R/O or Backup volume as SB_RDONLY when
mounting it.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
---
 fs/afs/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/afs/super.c b/fs/afs/super.c
index e95fb4cb4fcd..a01a0fb2cdbb 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -407,8 +407,10 @@ static int afs_validate_fc(struct fs_context *fc)
 			return PTR_ERR(volume);
 
 		ctx->volume = volume;
-		if (volume->type != AFSVL_RWVOL)
+		if (volume->type != AFSVL_RWVOL) {
 			ctx->flock_mode = afs_flock_mode_local;
+			fc->sb_flags |= SB_RDONLY;
+		}
 	}
 
 	return 0;