netdev - Re: [Patch net-next v2] net: dump more useful information in netdev_rx_csum

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Message-ID: <CAF=yD-JACLoK0eitnvH9VcDr5fJG+z-NULBgQFgbAeyt+PyR7A@mail.gmail.com>
Date:   Tue, 13 Nov 2018 11:13:45 -0800
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>
Subject: Re: [Patch net-next v2] net: dump more useful information in netdev_rx_csum_fault()

On Tue, Nov 13, 2018 at 10:14 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Tue, Nov 13, 2018 at 10:01 AM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > On Mon, Nov 12, 2018 at 2:49 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > >
> > > Currently netdev_rx_csum_fault() only shows a device name,
> > > we need more information about the skb for debugging csum
> > > failures.
> > >
> > > Sample output:
> > >
> > >  ens3: hw csum failure
> > >  dev features: 0x0000000000014b89
> > >  skb len=84 data_len=0 pkt_type=0 gso_size=0 gso_type=0 nr_frags=0 ip_summed=0 csum=0 csum_complete_sw=0 csum_valid=0 csum_level=0
> >
> > Recent issues were protocol dependent, including whether vlan headers
> > were present. Perhaps also print skb vlan fields and even the first N
> > bytes of data to inspect protocol headers? Also skb_iif, esp. if this
> > differs from dev->ifindex.
>
> Pawel's case seems to be vlan related, however, as I mentioned,
> my case is neither vlan nor RXFCS related.
>
> Ideally, we should dump the whole packet in order to verify the
> correctness of the checksum. :) It is not easy to do so given
> how complex an skb is now. This is why I only select a few skb
> fields to dump. I am pretty sure this can't cover all cases, you
> can always add more for your need in the future.

Sounds good. This patch is definitely useful as is.

Also, instead of adding code to print a (partial) packet header to
the kernel log, it may make more sense to export the skb to a
drop monitor over netlink or a perf buffer.