ext4 crypto: add encryption key management facilities

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
index 9d5d2e5..6a7c0c0 100644
--- a/fs/ext4/ext4_crypto.h
+++ b/fs/ext4/ext4_crypto.h
@@ -55,6 +55,9 @@
 #define EXT4_AES_256_XTS_KEY_SIZE 64
 #define EXT4_MAX_KEY_SIZE 64
 
+#define EXT4_KEY_DESC_PREFIX "ext4:"
+#define EXT4_KEY_DESC_PREFIX_SIZE 5
+
 struct ext4_encryption_key {
 	uint32_t mode;
 	char raw[EXT4_MAX_KEY_SIZE];