Miklos, As you observed, the sb->s_uuid field is not always filled by filesystems. Consumers, like overlayfs, that wish to use this field can check if is zeroed out as an indication for valid value. Christoph suggested to make the test more explicit and require the filesystems that fill the s_uuid field to set a super block flag. Do you agree with the proposed API? The first patch in the series defines the flag. If you push this patch through your tree to Al or Linus, then filesystem maintainers could later pick the individual patches to their trees. The xfs patch is based on a patch I already sent to Darrick for filling out the s_uuid field. Thanks, Amir. Amir Goldstein (5): vfs: define a flag to indicate sb->s_uuid is available ext4: set the super block SB_I_HAVE_UUID flag f2fs: set the super block SB_I_HAVE_UUID flag ocfs2: set the super block SB_I_HAVE_UUID flag xfs: set the super block SB_I_HAVE_UUID flag fs/ext4/super.c | 1 + fs/f2fs/super.c | 1 + fs/ocfs2/super.c | 1 + fs/xfs/xfs_mount.c | 1 + include/linux/fs.h | 3 +++ 5 files changed, 7 insertions(+) -- 2.7.4
