Unionfs: set our superblock a/m/ctime granularity

Set it to 1 ns, because we could be stacked on top of file systems with such
granularity.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/unionfs/main.c b/fs/unionfs/main.c
index 9371c2ef680a226f508d796a5be17ed0f922c387..e0ebca8cd68757bbbc8e8e7eb9a8b4dda5d554c9 100644 (file)
--- a/fs/unionfs/main.c
+++ b/fs/unionfs/main.c
@@ -732,6 +732,13 @@ static int unionfs_read_super(struct super_block *sb, void *raw_data,
        /* max Bytes is the maximum bytes from highest priority branch */
        sb->s_maxbytes = unionfs_lower_super_idx(sb, 0)->s_maxbytes;
 
+       /*
+        * Our c/m/atime granularity is 1 ns because we may stack on file
+        * systems whose granularity is as good.  This is important for our
+        * time-based cache coherency.
+        */
+       sb->s_time_gran = 1;
+
        sb->s_op = &unionfs_sops;
        init_export_op(sb);