fs/fat: implement fsuuid command

The FAT file system does not have a UUID but a 4 byte volume ID.
Let the fsuuid command show it in XXXX-XXXX format.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

fs/fat/fat.c

@@ -1377,3 +1377,21 @@ void fat_closedir(struct fs_dir_stream *dirs)
 void fat_close(void)
 {
 }
+
+int fat_uuid(char *uuid_str)
+{
+	boot_sector bs;
+	volume_info volinfo;
+	int fatsize;
+	int ret;
+	u8 *id;
+
+	ret = read_bootsectandvi(&bs, &volinfo, &fatsize);
+	if (ret)
+		return ret;
+
+	id = volinfo.volume_id;
+	sprintf(uuid_str, "%02X%02X-%02X%02X", id[3], id[2], id[1], id[0]);
+
+	return 0;
+}

fs/fs.c

@@ -194,7 +194,7 @@ static struct fstype_info fstypes[] = {
 		.unlink = fs_unlink_unsupported,
 		.mkdir = fs_mkdir_unsupported,
 #endif
-		.uuid = fs_uuid_unsupported,
+		.uuid = fat_uuid,
 		.opendir = fat_opendir,
 		.readdir = fat_readdir,
 		.closedir = fat_closedir,

include/fat.h

@@ -212,4 +212,16 @@ int fat_unlink(const char *filename);
 int fat_mkdir(const char *dirname);
 void fat_close(void);
 void *fat_next_cluster(fat_itr *itr, unsigned int *nbytes);
+
+/**
+ * fat_uuid() - get FAT volume ID
+ *
+ * The FAT volume ID returned in @uuid_str as hexadecimal number in XXXX-XXXX
+ * format.
+ *
+ * @uuid_str:	caller allocated buffer of at least 10 bytes for the volume ID
+ * Return:	0 on success
+ */
+int fat_uuid(char *uuid_str);
+
 #endif /* _FAT_H_ */