fs: make it possible to read the filesystem UUID

Some filesystems have a UUID stored in its superblock. To
allow using root=UUID=... for the kernel command line we
need a way to read-out the filesystem UUID.

changes rfc -> v1:
 - make the environment variable an option parameter. If not
   given, the UUID is printed out. If given, it is stored in the env
   variable.
 - corrected typos
 - return error codes

changes v1 -> v2:
 - fix return code of do_fs_uuid(..)
 - document do_fs_uuid(..)
 - implement fs_uuid_unsuported(..) be more consistent with the
   way other optional functionality works

changes v2 -> v3:
 - change ext4fs_uuid(..) to make use of #if .. #else .. #endif
   construct to get rid of unreachable code

Hit any key to stop autoboot:  0
=> fsuuid
fsuuid - Look up a filesystem UUID

Usage:
fsuuid <interface> <dev>:<part>
    - print filesystem UUID
fsuuid <interface> <dev>:<part> <varname>
    - set environment variable to filesystem UUID

=> fsuuid mmc 0:1
d9f9fc05-45ae-4a36-a616-fccce0e4f887
=> fsuuid mmc 0:2
eb3db83c-7b28-499f-95ce-9e0bb21cda81
=> fsuuid mmc 0:1 uuid1
=> fsuuid mmc 0:2 uuid2
=> printenv uuid1
uuid1=d9f9fc05-45ae-4a36-a616-fccce0e4f887
=> printenv uuid2
uuid2=eb3db83c-7b28-499f-95ce-9e0bb21cda81
=>

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Acked-by: Stephen Warren <swarren@nvidia.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
index cbdc220..87d5128 100644
--- a/fs/ext4/ext4fs.c
+++ b/fs/ext4/ext4fs.c
@@ -231,3 +231,18 @@ int ext4_read_file(const char *filename, void *buf, int offset, int len)
 
 	return len_read;
 }
+
+int ext4fs_uuid(char *uuid_str)
+{
+	if (ext4fs_root == NULL)
+		return -1;
+
+#ifdef CONFIG_LIB_UUID
+	uuid_bin_to_str((unsigned char *)ext4fs_root->sblock.unique_id,
+			uuid_str, UUID_STR_FORMAT_STD);
+
+	return 0;
+#else
+	return -ENOSYS;
+#endif
+}