lib: introduce crc_t10dif_update()

This introduces crc_t10dif_update() which enables to calculate CRC
for a block which straddles multiple SG elements by calling multiple
times.  This also converts crc_t10dif() to use crc_t10dif_update() as
they are almost same.

(remove extra function call in crc_t10dif() and crc_t10dif_update -
 Tim + Herbert)

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: target-devel@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

include/linux/crc-t10dif.h

@@ -9,5 +9,6 @@
 extern __u16 crc_t10dif_generic(__u16 crc, const unsigned char *buffer,
 				size_t len);
 extern __u16 crc_t10dif(unsigned char const *, size_t);
+extern __u16 crc_t10dif_update(__u16 crc, unsigned char const *, size_t);
 
 #endif

lib/crc-t10dif.c

@@ -19,7 +19,7 @@
 static struct crypto_shash *crct10dif_tfm;
 static struct static_key crct10dif_fallback __read_mostly;
 
-__u16 crc_t10dif(const unsigned char *buffer, size_t len)
+__u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len)
 {
 	struct {
 		struct shash_desc shash;
@@ -28,17 +28,23 @@ __u16 crc_t10dif(const unsigned char *buffer, size_t len)
 	int err;
 
 	if (static_key_false(&crct10dif_fallback))
-		return crc_t10dif_generic(0, buffer, len);
+		return crc_t10dif_generic(crc, buffer, len);
 
 	desc.shash.tfm = crct10dif_tfm;
 	desc.shash.flags = 0;
-	*(__u16 *)desc.ctx = 0;
+	*(__u16 *)desc.ctx = crc;
 
 	err = crypto_shash_update(&desc.shash, buffer, len);
 	BUG_ON(err);
 
 	return *(__u16 *)desc.ctx;
 }
+EXPORT_SYMBOL(crc_t10dif_update);
+
+__u16 crc_t10dif(const unsigned char *buffer, size_t len)
+{
+	return crc_t10dif_update(0, buffer, len);
+}
 EXPORT_SYMBOL(crc_t10dif);
 
 static int __init crc_t10dif_mod_init(void)