netdev - Re: [PATCH] packet: Allow packets with only a header (but no payload)

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Message-ID: <CAFBinCB4xOBzxwkEQYrpi1q7Xm4_-hpj2jUE2r-fQ5f2grjZ=Q@mail.gmail.com>
Date:	Tue, 21 Jul 2015 18:38:12 +0200
From:	Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:	Willem de Bruijn <willemb@...gle.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	David Miller <davem@...emloft.net>, mostrows@...thlink.net
Subject: Re: [PATCH] packet: Allow packets with only a header (but no payload)

Hi Willem,

On Tue, Jul 21, 2015 at 6:28 PM, Willem de Bruijn <willemb@...gle.com> wrote:
> Interesting. 9c7077622dd9 only extended the check from tpacket_snd to
> packet_snd to make the two paths equivalent. The existing check had the
> ominous statement
>
>     /* net device doesn't like empty head */
OK, I guess it's best to find out what the purpose of this comment is.

> so allowing a header-only packet while correct in your case may not be
> safe in some edge cases (specific device drivers?).
I'm wondering how a good fix would look like (I can think of a few
things, like renaming hard_header_len to something min_packet_size)?
I am open for suggestions since I have zero knowledge about the inner
workings of the packet framework.

> This was also discussed previously
>
>   http://www.spinics.net/lists/netdev/msg309677.html
>
> In any case, I don't think that reverting the patch and restoring the old
> inconsistent state is a fix.
I totally agree with you that it's a bad fix if this means that we
could break other drivers.
My primary goal was to fix PPPoE connections - I guess I should have
simply added "RFC" to the subject.


Regards,
Martin
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