[PATCH 1/5] vfs: define a flag to indicate sb->s_uuid is available

[Amir Goldstein <amir73il@gmail.com>]

Overlayfs would like to make use of underlying filesystem's
sb->s_uuid, but not all filesytems fill this field.

Define a flag to be set by filesystems that do fill the s_uuid
field, so let consumers like overlayfs know that the content
of this field is valid.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 include/linux/fs.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 80daadf..de913b4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1272,6 +1272,9 @@ struct mm_struct;
 /* sb->s_iflags to limit user namespace mounts */
 #define SB_I_USERNS_VISIBLE		0x00000010 /* fstype already mounted */
 
+/* sb->s_iflags for optional information available in super_block struct */
+#define SB_I_HAVE_UUID			0x00000100 /* s_uuid */
+
 /* Possible states of 'frozen' field */
 enum {
 	SB_UNFROZEN = 0,		/* FS is unfrozen */
-- 
2.7.4