netdev - Re: [PATCH] bnx2x: drop packets where gso

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Message-ID: <87a82f3zry.fsf@linkitivity.dja.id.au>
Date:   Fri, 01 Sep 2017 12:42:41 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, tlfalcon@...ux.vnet.ibm.com,
        Yuval.Mintz@...ium.com, ariel.elior@...ium.com,
        everest-linux-l2@...ium.com, jay.vosburgh@...onical.com
Subject: Re: [PATCH] bnx2x: drop packets where gso_size is too big for hardware

Eric Dumazet <eric.dumazet@...il.com> writes:

> If you had this test in bnx2x_features_check(), packet could be
> segmented by core networking stack before reaching bnx2x_start_xmit() by
> clearing NETIF_F_GSO_MASK
>
> -> No drop would be involved.

Thanks for the pointer - networking code is all a bit new to me.

I'm just struggling at the moment to figure out what the right way to
calculate the length. My original patch uses gso_size + hlen, but:

 - On reflection, while this solves the immediate bug, I'm not 100% sure
   this is the right thing to be calculating

 - If it is, then we have the problem that hlen is calculated in a bunch
   of weird and wonderful ways which make it a nightmare to extract.

Yuval (or anyone else who groks the driver properly) - what's the right
test to be doing here to make sure we don't write to much data to the
card?

Regards,
Daniel