sctp: Clean up sctp checksumming code

The sctp crc32c checksum is always generated in little endian.
So, we clean up the code to treat it as little endian and remove
all the __force casts.

Suggested by Herbert Xu.
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sctp.h

@@ -60,7 +60,7 @@ typedef struct sctphdr {
 	__be16 source;
 	__be16 dest;
 	__be32 vtag;
-	__be32 checksum;
+	__le32 checksum;
 } __attribute__((packed)) sctp_sctphdr_t;
 
 #ifdef __KERNEL__

include/net/sctp/checksum.h

@@ -46,14 +46,14 @@
 #include <net/sctp/sctp.h>
 #include <linux/crc32c.h>
 
-static inline __be32 sctp_crc32c(__be32 crc, u8 *buffer, u16 length)
+static inline __u32 sctp_crc32c(__u32 crc, u8 *buffer, u16 length)
 {
-	return (__force __be32)crc32c((__force u32)crc, buffer, length);
+	return crc32c(crc, buffer, length);
 }
 
-static inline __be32 sctp_start_cksum(__u8 *buffer, __u16 length)
+static inline __u32 sctp_start_cksum(__u8 *buffer, __u16 length)
 {
-	__be32 crc = ~cpu_to_be32(0);
+	__u32 crc = ~(__u32)0;
 	__u8  zero[sizeof(__u32)] = {0};
 
 	/* Optimize this routine to be SCTP specific, knowing how
@@ -72,12 +72,12 @@ static inline __be32 sctp_start_cksum(__u8 *buffer, __u16 length)
 	return crc;
 }
 
-static inline __be32 sctp_update_cksum(__u8 *buffer, __u16 length, __be32 crc32)
+static inline __u32 sctp_update_cksum(__u8 *buffer, __u16 length, __u32 crc32)
 {
 	return sctp_crc32c(crc32, buffer, length);
 }
 
-static inline __be32 sctp_end_cksum(__be32 crc32)
+static inline __le32 sctp_end_cksum(__be32 crc32)
 {
-	return (__force __be32)~cpu_to_le32((__force u32)crc32);
+	return cpu_to_le32(~crc32);
 }

net/sctp/input.c

@@ -83,14 +83,15 @@ static inline int sctp_rcv_checksum(struct sk_buff *skb)
 {
 	struct sk_buff *list = skb_shinfo(skb)->frag_list;
 	struct sctphdr *sh = sctp_hdr(skb);
-	__be32 cmp = sh->checksum;
-	__be32 val = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
+	__le32 cmp = sh->checksum;
+	__le32 val;
+	__u32 tmp = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
 
 	for (; list; list = list->next)
-		val = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
-					val);
+		tmp = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
+					tmp);
 
-	val = sctp_end_cksum(val);
+	val = sctp_end_cksum(tmp);
 
 	if (val != cmp) {
 		/* CRC failure, dump it. */

net/sctp/output.c

@@ -367,7 +367,6 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 	struct sctp_transport *tp = packet->transport;
 	struct sctp_association *asoc = tp->asoc;
 	struct sctphdr *sh;
-	__be32 crc32 = cpu_to_be32(0);
 	struct sk_buff *nskb;
 	struct sctp_chunk *chunk, *tmp;
 	struct sock *sk;
@@ -532,16 +531,15 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
 	 */
 	if (!sctp_checksum_disable && !(dst->dev->features & NETIF_F_NO_CSUM)) {
-		crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
-		crc32 = sctp_end_cksum(crc32);
+		__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
 		nskb->ip_summed = CHECKSUM_UNNECESSARY;
 
-	/* 3) Put the resultant value into the checksum field in the
-	 *    common header, and leave the rest of the bits unchanged.
-	 */
-	sh->checksum = crc32;
-
 	/* IP layer ECN support
 	 * From RFC 2481
 	 *  "The ECN-Capable Transport (ECT) bit would be set by the