eCryptfs: set inode key only once per crypto operation

There is no need to keep re-setting the same key for any given eCryptfs inode.
This patch optimizes the use of the crypto API and helps performance a bit.
Signed-off-by: Trevor Highland <trevor.highland@gmail.com>
Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ecryptfs/crypto.c

@@ -355,8 +355,11 @@ static int encrypt_scatterlist(struct ecryptfs_crypt_stat *crypt_stat,
 	}
 	/* Consider doing this once, when the file is opened */
 	mutex_lock(&crypt_stat->cs_tfm_mutex);
+	if (!(crypt_stat->flags & ECRYPTFS_KEY_SET)) {
 		rc = crypto_blkcipher_setkey(crypt_stat->tfm, crypt_stat->key,
 					     crypt_stat->key_size);
+		crypt_stat->flags |= ECRYPTFS_KEY_SET;
+	}
 	if (rc) {
 		ecryptfs_printk(KERN_ERR, "Error setting key; rc = [%d]\n",
 				rc);

fs/ecryptfs/ecryptfs_kernel.h

@@ -234,6 +234,7 @@ struct ecryptfs_crypt_stat {
 #define ECRYPTFS_KEY_VALID          0x00000080
 #define ECRYPTFS_METADATA_IN_XATTR  0x00000100
 #define ECRYPTFS_VIEW_AS_ENCRYPTED  0x00000200
+#define ECRYPTFS_KEY_SET            0x00000400
 	u32 flags;
 	unsigned int file_version;
 	size_t iv_bytes;