Subject: Re: [PATCH] sctp: remove unnecessary byteshifting, calculate crc in big-endian

From: Vlad Yasevich <[email-masked]>
Date: Wed, 09 Jul 2008 16:59:36 -0400

Harvey Harrison wrote:
> Signed-off-by: Harvey Harrison <[email-masked]>
> ---
>  include/net/sctp/checksum.h            |   23 ++++++++++++++---------
>  net/ipv4/netfilter/nf_nat_proto_sctp.c |    4 ++--
>  net/sctp/input.c                       |    4 ++--
>  net/sctp/output.c                      |    4 ++--
>  4 files changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/include/net/sctp/checksum.h b/include/net/sctp/checksum.h
> index ba75c67..b799fb2 100644
> --- a/include/net/sctp/checksum.h
> +++ b/include/net/sctp/checksum.h
> @@ -46,9 +46,14 @@
>  #include <net/sctp/sctp.h>
>  #include <linux/crc32c.h>
>  
> -static inline __u32 sctp_start_cksum(__u8 *buffer, __u16 length)
> +static inline __be32 sctp_crc32c(__be32 crc, u8 *buffer, u16 length)
>  {
> -	__u32 crc = ~(__u32) 0;
> +	return (__force __be32)crc32c((__force u32)crc, buffer, length);
> +}
> +
> +static inline __be32 sctp_start_cksum(__u8 *buffer, __u16 length)
> +{
> +	__be32 crc = ~cpu_to_be32(0);
>  	__u8  zero[sizeof(__u32)] = {0};
>  
>  	/* Optimize this routine to be SCTP specific, knowing how
> @@ -56,23 +61,23 @@ static inline __u32 sctp_start_cksum(__u8 *buffer, __u16 length)
>  	 */
>  
>  	/* Calculate CRC up to the checksum. */
> -	crc = crc32c(crc, buffer, sizeof(struct sctphdr) - sizeof(__u32));
> +	crc = sctp_crc32c(crc, buffer, sizeof(struct sctphdr) - sizeof(__u32));
>  
>  	/* Skip checksum field of the header. */
> -	crc = crc32c(crc, zero, sizeof(__u32));
> +	crc = sctp_crc32c(crc, zero, sizeof(__u32));
>  
>  	/* Calculate the rest of the CRC. */
> -	crc = crc32c(crc, &buffer[sizeof(struct sctphdr)],
> +	crc = sctp_crc32c(crc, &buffer[sizeof(struct sctphdr)],
>  			    length - sizeof(struct sctphdr));
>  	return crc;
>  }
>  
> -static inline __u32 sctp_update_cksum(__u8 *buffer, __u16 length, __u32 crc32)
> +static inline __be32 sctp_update_cksum(__u8 *buffer, __u16 length, __be32 crc32)
>  {
> -	return crc32c(crc32, buffer, length);
> +	return sctp_crc32c(crc32, buffer, length);
>  }
>  
> -static inline __u32 sctp_end_cksum(__u32 crc32)
> +static inline __be32 sctp_end_cksum(__be32 crc32)
>  {
> -	return ntohl(~crc32);
> +	return ~crc32;
>  }
> diff --git a/net/ipv4/netfilter/nf_nat_proto_sctp.c b/net/ipv4/netfilter/nf_nat_proto_sctp.c
> index 82e4c0e..65e470b 100644
> --- a/net/ipv4/netfilter/nf_nat_proto_sctp.c
> +++ b/net/ipv4/netfilter/nf_nat_proto_sctp.c
> @@ -36,7 +36,7 @@ sctp_manip_pkt(struct sk_buff *skb,
>  	sctp_sctphdr_t *hdr;
>  	unsigned int hdroff = iphdroff + iph->ihl*4;
>  	__be32 oldip, newip;
> -	u32 crc32;
> +	__be32 crc32;
>  
>  	if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
>  		return false;
> @@ -61,7 +61,7 @@ sctp_manip_pkt(struct sk_buff *skb,
>  		crc32 = sctp_update_cksum((u8 *)skb->data, skb_headlen(skb),
>  					  crc32);
>  	crc32 = sctp_end_cksum(crc32);
> -	hdr->checksum = htonl(crc32);
> +	hdr->checksum = crc32;
>  
>  	return true;
>  }
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index d354a23..463d529 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -82,8 +82,8 @@ 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);
> -	__u32 cmp = ntohl(sh->checksum);
> -	__u32 val = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
> +	__be32 cmp = sh->checksum;
> +	__be32 val = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
>  
>  	for (; list; list = list->next)
>  		val = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index abcd00d..e2158ad 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -364,7 +364,7 @@ int sctp_packet_transmit(struct sctp_packet *packet)
>  	struct sctp_transport *tp = packet->transport;
>  	struct sctp_association *asoc = tp->asoc;
>  	struct sctphdr *sh;
> -	__u32 crc32 = 0;
> +	__be32 crc32 = cpu_to_be32(0);

Does this actually do anything?

Otherwise, good clean-up. Thanks

-vlad

>  	struct sk_buff *nskb;
>  	struct sctp_chunk *chunk, *tmp;
>  	struct sock *sk;
> @@ -537,7 +537,7 @@ int sctp_packet_transmit(struct sctp_packet *packet)
>  	/* 3) Put the resultant value into the checksum field in the
>  	 *    common header, and leave the rest of the bits unchanged.
>  	 */
> -	sh->checksum = htonl(crc32);
> +	sh->checksum = crc32;
>  
>  	/* IP layer ECN support
>  	 * From RFC 2481