sctp: add feature bit for SCTP offload in hardware

this is the sctp code to enable hardware crc32c offload for
adapters that support it.

Originally by: Vlad Yasevich <vladislav.yasevich@hp.com>

modified by Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -670,7 +670,9 @@ struct net_device
 #define NETIF_F_GRO		16384	/* Generic receive offload */
 #define NETIF_F_LRO		32768	/* large receive offload */
 
+/* the GSO_MASK reserves bits 16 through 23 */
 #define NETIF_F_FCOE_CRC	(1 << 24) /* FCoE CRC32 */
+#define NETIF_F_SCTP_CSUM	(1 << 25) /* SCTP checksum offload */
 
 	/* Segmentation offload features */
 #define NETIF_F_GSO_SHIFT	16

net/sctp/output.c

@@ -412,6 +412,7 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 
 	/* Build the SCTP header.  */
 	sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
+	skb_reset_transport_header(nskb);
 	sh->source = htons(packet->source_port);
 	sh->dest   = htons(packet->destination_port);
 
@@ -527,15 +528,25 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 	 * Note: Adler-32 is no longer applicable, as has been replaced
 	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 	 */
-	if (!sctp_checksum_disable && !(dst->dev->features & NETIF_F_NO_CSUM)) {
+	if (!sctp_checksum_disable &&
+	    !(dst->dev->features & (NETIF_F_NO_CSUM | NETIF_F_SCTP_CSUM))) {
 		__u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 
 		/* 3) Put the resultant value into the checksum field in the
 		 *    common header, and leave the rest of the bits unchanged.
 		 */
 		sh->checksum = sctp_end_cksum(crc32);
-	} else
+	} else {
+		if (dst->dev->features & NETIF_F_SCTP_CSUM) {
+			/* no need to seed psuedo checksum for SCTP */
+			nskb->ip_summed = CHECKSUM_PARTIAL;
+			nskb->csum_start = (skb_transport_header(nskb) -
+			                    nskb->head);
+			nskb->csum_offset = offsetof(struct sctphdr, checksum);
+		} else {
 			nskb->ip_summed = CHECKSUM_UNNECESSARY;
+		}
+	}
 
 	/* IP layer ECN support
 	 * From RFC 2481