uuid: Provide a GUID generator for raw buffer

In some cases we would like to generate a GUID and export it.  Though it
would require either casting to internal kernel types or an intermediate
buffer. Instead we may achieve this by supplying a pointer to raw buffer
and make a complimentary API to existing one for UUIDs.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David Sterba <dsterba@suse.com>

include/linux/uuid.h

@@ -84,6 +84,7 @@ static inline bool uuid_is_null(const uuid_t *uuid)
 }
 
 void generate_random_uuid(unsigned char uuid[16]);
+void generate_random_guid(unsigned char guid[16]);
 
 extern void guid_gen(guid_t *u);
 extern void uuid_gen(uuid_t *u);

lib/uuid.c

@@ -40,6 +40,16 @@ void generate_random_uuid(unsigned char uuid[16])
 }
 EXPORT_SYMBOL(generate_random_uuid);
 
+void generate_random_guid(unsigned char guid[16])
+{
+	get_random_bytes(guid, 16);
+	/* Set GUID version to 4 --- truly random generation */
+	guid[7] = (guid[7] & 0x0F) | 0x40;
+	/* Set the GUID variant to DCE */
+	guid[8] = (guid[8] & 0x3F) | 0x80;
+}
+EXPORT_SYMBOL(generate_random_guid);
+
 static void __uuid_gen_common(__u8 b[16])
 {
 	prandom_bytes(b, 16);