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>

2 files changed, 58 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
+}
diff --git a/fs/fs.c b/fs/fs.c
index dd680f3..e4ad6bc 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -15,6 +15,7 @@
  */
 
 #include <config.h>
+#include <errno.h>
 #include <common.h>
 #include <part.h>
 #include <ext4fs.h>
@@ -67,6 +68,11 @@ static inline void fs_close_unsupported(void)
 {
 }
 
+static inline int fs_uuid_unsupported(char *uuid_str)
+{
+	return -1;
+}
+
 struct fstype_info {
 	int fstype;
 	/*
@@ -86,6 +92,7 @@ struct fstype_info {
 	int (*read)(const char *filename, void *buf, int offset, int len);
 	int (*write)(const char *filename, void *buf, int offset, int len);
 	void (*close)(void);
+	int (*uuid)(char *uuid_str);
 };
 
 static struct fstype_info fstypes[] = {
@@ -100,6 +107,7 @@ static struct fstype_info fstypes[] = {
 		.size = fat_size,
 		.read = fat_read_file,
 		.write = fs_write_unsupported,
+		.uuid = fs_uuid_unsupported,
 	},
 #endif
 #ifdef CONFIG_FS_EXT4
@@ -113,6 +121,7 @@ static struct fstype_info fstypes[] = {
 		.size = ext4fs_size,
 		.read = ext4_read_file,
 		.write = fs_write_unsupported,
+		.uuid = ext4fs_uuid,
 	},
 #endif
 #ifdef CONFIG_SANDBOX
@@ -126,6 +135,7 @@ static struct fstype_info fstypes[] = {
 		.size = sandbox_fs_size,
 		.read = fs_read_sandbox,
 		.write = fs_write_sandbox,
+		.uuid = fs_uuid_unsupported,
 	},
 #endif
 	{
@@ -138,6 +148,7 @@ static struct fstype_info fstypes[] = {
 		.size = fs_size_unsupported,
 		.read = fs_read_unsupported,
 		.write = fs_write_unsupported,
+		.uuid = fs_uuid_unsupported,
 	},
 };
 
@@ -206,6 +217,13 @@ static void fs_close(void)
 	fs_type = FS_TYPE_ANY;
 }
 
+int fs_uuid(char *uuid_str)
+{
+	struct fstype_info *info = fs_get_info(fs_type);
+
+	return info->uuid(uuid_str);
+}
+
 int fs_ls(const char *dirname)
 {
 	int ret;
@@ -443,3 +461,28 @@ int do_save(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
 
 	return 0;
 }
+
+int do_fs_uuid(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
+		int fstype)
+{
+	int ret;
+	char uuid[37];
+	memset(uuid, 0, sizeof(uuid));
+
+	if (argc < 3 || argc > 4)
+		return CMD_RET_USAGE;
+
+	if (fs_set_blk_dev(argv[1], argv[2], fstype))
+		return 1;
+
+	ret = fs_uuid(uuid);
+	if (ret)
+		return CMD_RET_FAILURE;
+
+	if (argc == 4)
+		setenv(argv[3], uuid);
+	else
+		printf("%s\n", uuid);
+
+	return CMD_RET_SUCCESS;
+}