[PATCH v1 1/2] can: do not increase rx statistics when receiving CAN error frames

[Vincent MAILHOL]

On Wed. 24 Nov. 2021 à 06:01, Oliver Hartkopp <socketcan at hartkopp.net> wrote:
> On 23.11.21 12:53, Vincent Mailhol wrote:
> > CAN error skb is an interface specific to socket CAN. The CAN error
> > skb does not correspond to any actual CAN frame sent on the wire. Only
> > an error flag and a delimiter are transmitted when an error occurs
> > (c.f. ISO 11898-1 section 10.4.4.2 "Error flag").
> >
> > For this reason, it makes no sense to increment the rx_packets and
> > rx_bytes fields of struct net_device_stats because no actual payload
> > were transmitted on the wire.
> >
>
> (..)
>
> > diff --git a/drivers/net/can/dev/rx-offload.c b/drivers/net/can/dev/rx-offload.c
> > index 37b0cc65237b..bb47e9a49240 100644
> > --- a/drivers/net/can/dev/rx-offload.c
> > +++ b/drivers/net/can/dev/rx-offload.c
> > @@ -54,8 +54,10 @@ static int can_rx_offload_napi_poll(struct napi_struct *napi, int quota)
> >               struct can_frame *cf = (struct can_frame *)skb->data;
> >
> >               work_done++;
> > -             stats->rx_packets++;
> > -             stats->rx_bytes += cf->len;
> > +             if (!(cf->can_id & CAN_ERR_MASK)) {
>
> This looks wrong.

And it is.

> Did you think of CAN_ERR_FLAG ??

Yes, I will fix this in v2.

> > +                     stats->rx_packets++;
> > +                     stats->rx_bytes += cf->len;
> > +             }
> >               netif_receive_skb(skb);
>
> (..)
>
> > diff --git a/drivers/net/can/usb/ucan.c b/drivers/net/can/usb/ucan.c
> > index 1679cbe45ded..d582c39fc8d0 100644
> > --- a/drivers/net/can/usb/ucan.c
> > +++ b/drivers/net/can/usb/ucan.c
> > @@ -621,8 +621,10 @@ static void ucan_rx_can_msg(struct ucan_priv *up, struct ucan_message_in *m)
> >               memcpy(cf->data, m->msg.can_msg.data, cf->len);
> >
> >       /* don't count error frames as real packets */
> > -     stats->rx_packets++;
> > -     stats->rx_bytes += cf->len;
> > +     if (!(cf->can_id & CAN_ERR_FLAG)) {
>
> Ah, here we are :-)

Thank you!