On Mon, Mar 15, 2021 at 6:36 AM Alex Elder <el...@linaro.org> wrote:
>
> In rmnet_map_ipv4_ul_csum_header() and rmnet_map_ipv6_ul_csum_header()
> the offset within a packet at which checksumming should commence is
> calculated. This calculation involves byte swapping and a forced type
> conversion that makes it hard to understand.
>
> Simplify this by computing the offset in host byte order, then
> converting the result when assigning it into the header field.
>
> Signed-off-by: Alex Elder <el...@linaro.org>
> Reviewed-by: Bjorn Andersson <bjorn.anders...@linaro.org>
> ---
> .../ethernet/qualcomm/rmnet/rmnet_map_data.c | 22 ++++++++++---------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 21d38167f9618..bd1aa11c9ce59 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -197,12 +197,13 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
> struct rmnet_map_ul_csum_header *ul_header,
> struct sk_buff *skb)
> {
> - struct iphdr *ip4h = (struct iphdr *)iphdr;
> - __be16 *hdr = (__be16 *)ul_header, offset;
> + __be16 *hdr = (__be16 *)ul_header;
> + struct iphdr *ip4h = iphdr;
> + u16 offset;
> +
> + offset = skb_transport_header(skb) - (unsigned char *)iphdr;
> + ul_header->csum_start_offset = htons(offset);
Rather than using skb_transport_header the correct pointer to use is
probably skb_checksum_start. The two are essentially synonymous but
the checksumming code is supposed to use skb_checksum_start.
Alternatively you could look at possibly using skb_network_header_len
as that would be the same value assuming that both headers are the
outer headers. Then you could avoid the extra pointer overhead.
>
> - offset = htons((__force u16)(skb_transport_header(skb) -
> - (unsigned char *)iphdr));
> - ul_header->csum_start_offset = offset;
> ul_header->csum_insert_offset = skb->csum_offset;
> ul_header->csum_enabled = 1;
> if (ip4h->protocol == IPPROTO_UDP)
> @@ -239,12 +240,13 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
> struct rmnet_map_ul_csum_header *ul_header,
> struct sk_buff *skb)
> {
> - struct ipv6hdr *ip6h = (struct ipv6hdr *)ip6hdr;
> - __be16 *hdr = (__be16 *)ul_header, offset;
> + __be16 *hdr = (__be16 *)ul_header;
> + struct ipv6hdr *ip6h = ip6hdr;
> + u16 offset;
> +
> + offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
> + ul_header->csum_start_offset = htons(offset);
Same here.
>
> - offset = htons((__force u16)(skb_transport_header(skb) -
> - (unsigned char *)ip6hdr));
> - ul_header->csum_start_offset = offset;
> ul_header->csum_insert_offset = skb->csum_offset;
> ul_header->csum_enabled = 1;
>
> --
> 2.27.0
>
