Re: [PATCH RFC net-next v4 4/7] net: use skb->csum_not_inet to identify packets needing crc32c

[Tom Herbert <tom@herbertland.com>]

On Thu, Apr 20, 2017 at 6:38 AM, Davide Caratti <dcaratti@redhat.com> wrote:
> skb->csum_not_inet carries the indication on which algorithm is needed to
> compute checksum on skb in the transmit path, when skb->ip_summed is equal
> to CHECKSUM_PARTIAL. If skb carries a SCTP packet and crc32c hasn't been
> yet written in L4 header, skb->csum_not_inet is assigned to 1; otherwise,
> assume Internet Checksum is needed and thus set skb->csum_not_inet to 0.
>
> Suggested-by: Tom Herbert <tom@herbertland.com>
> Signed-off-by: Davide Caratti <dcaratti@redhat.com>
> ---
>  include/linux/skbuff.h | 16 +++++++++-------
>  net/core/dev.c         |  1 +
>  net/sched/act_csum.c   |  1 +
>  net/sctp/offload.c     |  1 +
>  net/sctp/output.c      |  1 +
>  5 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 927309e..419f4c8 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -189,12 +189,13 @@
>   *
>   *   NETIF_F_SCTP_CRC - This feature indicates that a device is capable of
>   *     offloading the SCTP CRC in a packet. To perform this offload the stack
> - *     will set ip_summed to CHECKSUM_PARTIAL and set csum_start and csum_offset
> - *     accordingly. Note the there is no indication in the skbuff that the
> - *     CHECKSUM_PARTIAL refers to an SCTP checksum, a driver that supports
> - *     both IP checksum offload and SCTP CRC offload must verify which offload
> - *     is configured for a packet presumably by inspecting packet headers; in
> - *     case, skb_crc32c_csum_help is provided to compute CRC on SCTP packets.
> + *     will set set csum_start and csum_offset accordingly, set ip_summed to
> + *     CHECKSUM_PARTIAL and set csum_not_inet to 1, to provide an indication in
> + *     the skbuff that the CHECKSUM_PARTIAL refers to CRC32c.
> + *     A driver that supports both IP checksum offload and SCTP CRC32c offload
> + *     must verify which offload is configured for a packet by testing the
> + *     value of skb->csum_not_inet; skb_crc32c_csum_help is provided to resolve
> + *     CHECKSUM_PARTIAL on skbs where csum_not_inet is set to 1.
>   *
>   *   NETIF_F_FCOE_CRC - This feature indicates that a device is capable of
>   *     offloading the FCOE CRC in a packet. To perform this offload the stack
> @@ -615,6 +616,7 @@ static inline bool skb_mstamp_after(const struct skb_mstamp *t1,
>   *     @wifi_acked_valid: wifi_acked was set
>   *     @wifi_acked: whether frame was acked on wifi or not
>   *     @no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
> + *     @csum_not_inet: use CRC32c to resolve CHECKSUM_PARTIAL
>   *     @dst_pending_confirm: need to confirm neighbour
>    *    @napi_id: id of the NAPI struct this skb came from
>   *     @secmark: security marking
> @@ -743,7 +745,7 @@ struct sk_buff {
>         __u8                    csum_valid:1;
>         __u8                    csum_complete_sw:1;
>         __u8                    csum_level:2;
> -       __u8                    __csum_bad_unused:1; /* one bit hole */
> +       __u8                    csum_not_inet:1;
>
>         __u8                    dst_pending_confirm:1;
>  #ifdef CONFIG_IPV6_NDISC_NODETYPE
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 77a2d73..9f56f87 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2642,6 +2642,7 @@ int skb_crc32c_csum_help(struct sk_buff *skb)
>         }
>         *(__le32 *)(skb->data + offset) = crc32c_csum;
>         skb->ip_summed = CHECKSUM_NONE;
> +       skb->csum_not_inet = 0;
>  out:
>         return ret;
>  }
> diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
> index ab6fdbd..3317a2f 100644
> --- a/net/sched/act_csum.c
> +++ b/net/sched/act_csum.c
> @@ -350,6 +350,7 @@ static int tcf_csum_sctp(struct sk_buff *skb, unsigned int ihl,
>         sctph->checksum = sctp_compute_cksum(skb,
>                                              skb_network_offset(skb) + ihl);
>         skb->ip_summed = CHECKSUM_NONE;
> +       skb->csum_not_inet = 0;
>
>         return 1;
>  }
> diff --git a/net/sctp/offload.c b/net/sctp/offload.c
> index 378f462..ef156ac 100644
> --- a/net/sctp/offload.c
> +++ b/net/sctp/offload.c
> @@ -35,6 +35,7 @@
>  static __le32 sctp_gso_make_checksum(struct sk_buff *skb)
>  {
>         skb->ip_summed = CHECKSUM_NONE;
> +       skb->csum_not_inet = 0;
>         return sctp_compute_cksum(skb, skb_transport_offset(skb));
>  }
>
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 1409a87..e2edf2e 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -538,6 +538,7 @@ static int sctp_packet_pack(struct sctp_packet *packet,
>         } else {
>  chksum:
>                 head->ip_summed = CHECKSUM_PARTIAL;
> +               head->csum_not_inet = 1;
>                 head->csum_start = skb_transport_header(head) - head->head;
>                 head->csum_offset = offsetof(struct sctphdr, checksum);
>         }
> --
> 2.7.4
>
Looks great!

Acked-by: Tom Herbert <tom@herbertland.com>