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Date: Tue, 6 Oct 2020 07:30:13 -0400 From: Willem de Bruijn <willemdebruijn.kernel@...il.com> To: Jacob Keller <jacob.e.keller@...el.com> Cc: Vladimir Oltean <vladimir.oltean@....com>, Network Development <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn <willemdebruijn.kernel@...il.com> Subject: Re: [PATCH net-next] net: always dump full packets with skb_dump On Mon, Oct 5, 2020 at 8:25 PM Jacob Keller <jacob.e.keller@...el.com> wrote: > > > > On 10/5/2020 7:48 AM, Vladimir Oltean wrote: > > Currently skb_dump has a restriction to only dump full packet for the > > first 5 socket buffers, then only headers will be printed. Remove this > > arbitrary and confusing restriction, which is only documented vaguely > > ("up to") in the comments above the prototype. > > > > So, this limitation appeared very clearly in the original commit, > 6413139dfc64 ("skbuff: increase verbosity when dumping skb data").. > > Searching the netdev list, that patch links back to this one as the > original idea: > > https://patchwork.ozlabs.org/project/netdev/patch/20181121021309.6595-2-xiyou.wangcong@gmail.com/ > > I can't find any further justification on that limit. I suppose the > primary reasoning being if you somehow call this function in a loop this > would avoid dumping the entire packet over and over? Not in a loop per se, but indeed to avoid unbounded writing to the kernel log. skb_dump is called from skb_warn_bad_offload and netdev_rx_csum_fault. Previously when these were triggered, a few example bad packets were sufficient to debug the issue. A full dump can add a lot of data to the kernel log, so I limited to what is strictly needed.
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