netdev - Re: UDP GRO do not restore ervery UDP Packet

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Message-ID: <542d117e1b05aa4b87943e6f705ecf9c19bf96fe.camel@redhat.com>
Date:   Tue, 09 Apr 2019 09:58:19 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Sean Tong <seantong114@...il.com>, netdev <netdev@...r.kernel.org>
Subject: Re: UDP GRO do not restore ervery UDP Packet

Hi,

On Tue, 2019-04-09 at 14:09 +0800, Sean Tong wrote:
> For example, recvmsg returns  a packet size 50  of  and gso_size of
> 24, so the UDP packets is restored without knowing whether it is
> 24+24+2 split into 3 packets or 24+26 split into 2 pakcets.
> Is there any way to get the last UDP packet size or number of merged
> UDP packets?

In the described scenario, the ingress packets lengths are: 24, 24, 2.

The sequence 24, 26 is not possible.

Generally speaking, if the aggregated packet length is not a multiple
of gro_size, the length of the last UDP packet aggregated in the GRO
one is: 

<GRO packet size> % gso_size.

(2, in the above example).

If you observe something differnt, it's a bug and must be fixed -
please provide detailed setup information, thanks!

Paolo