[PATCH] tmpfs: generate random sb->s_uuid

[Amir Goldstein <amir73il@xxxxxxxxx>]

This is used by overlayfs to encode intrasystem unique file handles.

Suggested-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 mm/shmem.c | 1 +
 1 file changed, 1 insertion(+)

Miklos,

Attached the simple patch you suggested.
With this patch the unionmount-testsuite run:
./run --ov=0 --samefs

Passes with (default) tmpfs as samefs.

Hugh,

Can you please Ack.

FYI, both xfs and ubifs have patches queued to export thier on-disk
uuid to sb->s_uuid.

Thanks,
Amir.

diff --git a/mm/shmem.c b/mm/shmem.c
index e67d6ba..b73f832 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3761,6 +3761,7 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
 #ifdef CONFIG_TMPFS_POSIX_ACL
 	sb->s_flags |= MS_POSIXACL;
 #endif
+	generate_random_uuid(sb->s_uuid);
 
 	inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
 	if (!inode)
-- 
2.7.4