Re: [PATCH v3 4/5] tcp: Update TCP checksum using an iovec array

[Laurent Vivier <lvivier@redhat.com>]

On 26/09/2024 15:29, Laurent Vivier wrote:
> TCP header and payload are supposed to be in the same buffer,
> and tcp_update_check_tcp4()/tcp_update_check_tcp6() compute
> the checksum from the base address of the header using the
> length of the IP payload.
> 
> In the future (for vhost-user) we need to dispatch the TCP header and
> the TCP payload through several buffers. To be able to manage that, we
> provide an iovec array that points to the data of the TCP frame.
> We provide also an offset to be able to provide an array that contains
> the TCP frame embedded in an lower level frame, and this offset points
> to the TCP header inside the iovec array.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>   checksum.c |   1 -
>   tcp.c      | 127 +++++++++++++++++++++++++++++++++++++++++------------
>   2 files changed, 99 insertions(+), 29 deletions(-)
...
>   /**
>    * tcp_update_check_tcp6() - Calculate TCP checksum for IPv6
> - * @ip6h:	IPv6 header
> - * @bp:		TCP header followed by TCP payload
> - */
> -static void tcp_update_check_tcp6(const struct ipv6hdr *ip6h,
> -				  struct tcp_payload_t *bp)
> + * @src:	IPv6 source address
> + * @dst:	IPv6 destination address
> + * @iov:	Pointer to the array of IO vectors
> + * @iov_cnt:	Length of the array
> + * @l4offset:	IPv6 payload offset in the iovec array
> + */
> +void tcp_update_check_tcp6(const struct in6_addr *src,
> +			   const struct in6_addr *dst,
> +			   const struct iovec *iov, int iov_cnt,
> +			   size_t l4offset)
>   {
> -	uint16_t l4len = ntohs(ip6h->payload_len);
> -	uint32_t sum = proto_ipv6_header_psum(l4len, IPPROTO_TCP,
> -					      &ip6h->saddr, &ip6h->daddr);
> +	size_t check_ofs;
> +	__sum16 *check;
> +	int check_idx;
> +	uint32_t sum;
> +
> +	sum = proto_ipv6_header_psum(iov_size(iov, iov_cnt) - l4offset,
> +				     IPPROTO_TCP, src, dst);
>   
> -	bp->th.check = 0;
> -	bp->th.check = csum(bp, l4len, sum);
> +	check_idx = iov_skip_bytes(iov, iov_cnt,
> +				   l4offset + offsetof(struct tcphdr, check),
> +				   &check_ofs);
> +
> +	if (check_idx >= iov_cnt)
> +		die("TCP6 buffer is too small");
> +	if (check_ofs + sizeof(*check) > iov[check_idx].iov_len)
> +		die("TCP6 checksum field memory is not contiguous");
> +

I'm going to resend, I forgot to update tcp_update_check_tcp6().

Laurent