netdev - Re: [Patch net-next 2/2] net: dump whole skb data in netdev_rx_csum

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Date:   Thu, 22 Nov 2018 17:45:11 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [Patch net-next 2/2] net: dump whole skb data in netdev_rx_csum_fault()

On Wed, Nov 21, 2018 at 11:33 AM Saeed Mahameed <saeedm@...lanox.com> wrote:
>
> On Wed, 2018-11-21 at 10:26 -0800, Eric Dumazet wrote:
> > On Wed, Nov 21, 2018 at 10:17 AM Cong Wang <xiyou.wangcong@...il.com>
> > wrote:
> > > On Wed, Nov 21, 2018 at 5:05 AM Eric Dumazet <
> > > eric.dumazet@...il.com> wrote:
> > > >
> > > >
> > > > On 11/20/2018 06:13 PM, Cong Wang wrote:
> > > > > Currently, we only dump a few selected skb fields in
> > > > > netdev_rx_csum_fault(). It is not suffient for debugging
> > > > > checksum
> > > > > fault. This patch introduces skb_dump() which dumps skb mac
> > > > > header,
> > > > > network header and its whole skb->data too.
> > > > >
> > > > > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > > > > Cc: Eric Dumazet <edumazet@...gle.com>
> > > > > Cc: David Miller <davem@...emloft.net>
> > > > > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > > > > ---
> > > > > +     print_hex_dump(level, "skb data: ", DUMP_PREFIX_OFFSET,
> > > > > 16, 1,
> > > > > +                    skb->data, skb->len, false);
> > > >
> > > > As I mentioned to David, we want all the bytes that were maybe
> > > > already pulled
> > > >
> > > > (skb->head starting point, not skb->data)
> > >
> > > Hmm, with mac header and network header, it is effectively from
> > > skb->head, no?
> > > Is there anything between skb->head and mac header?
> >
> > Oh, I guess we wanted a single hex dump, or we need some user program
> > to be able to
> > rebuild from different memory zones the original CHECKSUM_COMPLETE
> > value.
> >
>
> Normally the driver keeps some headroom @skb->head, so the actual mac
> header starts @ skb->head + driver_specific_headroom

Good to know, but this headroom isn't covered by skb->csum, so
not useful here, right? The skb->csum for mlx5 only covers network
header and its payload.