ecryptfs: remove private bin2hex implementation

Calling sprintf in a loop is not very efficient, and in any case, we
already have an implementation of bin-to-hex conversion in lib/ which
we might as well use.

Note that ecryptfs_to_hex used to nul-terminate the destination (and
the kernel doc was wrong about the required output size), while
bin2hex doesn't. [All but one user of ecryptfs_to_hex explicitly
nul-terminates the result anyway.]

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
[tyhicks: Include <linux/kernel.h> in ecryptfs_kernel.h]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

fs/ecryptfs/crypto.c

@@ -41,21 +41,6 @@
 #define DECRYPT		0
 #define ENCRYPT		1
 
-/**
- * ecryptfs_to_hex
- * @dst: Buffer to take hex character representation of contents of
- *       src; must be at least of size (src_size * 2)
- * @src: Buffer to be converted to a hex string representation
- * @src_size: number of bytes to convert
- */
-void ecryptfs_to_hex(char *dst, char *src, size_t src_size)
-{
-	int x;
-
-	for (x = 0; x < src_size; x++)
-		sprintf(&dst[x * 2], "%.2x", (unsigned char)src[x]);
-}
-
 /**
  * ecryptfs_from_hex
  * @dst: Buffer to take the bytes from src hex; must be at least of

fs/ecryptfs/ecryptfs_kernel.h

@@ -31,6 +31,7 @@
 #include <crypto/skcipher.h>
 #include <keys/user-type.h>
 #include <keys/encrypted-type.h>
+#include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/fs_stack.h>
 #include <linux/namei.h>
@@ -51,7 +52,13 @@
 #define ECRYPTFS_XATTR_NAME "user.ecryptfs"
 
 void ecryptfs_dump_auth_tok(struct ecryptfs_auth_tok *auth_tok);
-extern void ecryptfs_to_hex(char *dst, char *src, size_t src_size);
+static inline void
+ecryptfs_to_hex(char *dst, char *src, size_t src_size)
+{
+	char *end = bin2hex(dst, src, src_size);
+	*end = '\0';
+}
+
 extern void ecryptfs_from_hex(char *dst, char *src, int dst_size);
 
 struct ecryptfs_key_record {