netdev - Re: [PATCH net-next] sock: don't enable netstamp for af

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Message-Id: <1445953468.1370159.421485969.5DA0A8B3@webmail.messagingengine.com>
Date:	Tue, 27 Oct 2015 14:44:28 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net-next] sock: don't enable netstamp for af_unix sockets



On Tue, Oct 27, 2015, at 14:19, Eric Dumazet wrote:
> On Tue, 2015-10-27 at 12:15 +0100, Hannes Frederic Sowa wrote:
> 
> > Also counter question: why is the netstamp code protected by a
> > static_key otherwise if not for trying to suppress the code path as
> > often as possible if not used? ;)
> 
> Any idea of why timestamping is asked on AF_UNIX in the first place ?

I guess syslog code want's to have more accurate timetstamps on when the
packet is send.

> For messages sent/received on af_unix sockets, in which place timestamp
> is taken ?

in unix_sendmsg on the sending unix socket (we check peer unix socket
for timestamp flag).

> Is it at the time skb is cooked and stored in receive queue, or the time
> it was dequeued ?

No, at time it is send by sendmsg on the sending socket.

> In any case, is your patch changing af_unix behavior ? It is not clear
> from your changelog...

No, af_unix logic does not pass this logic at all, so we don't need to
care about netstamp code. netstamp_needed is private to dev.c.

Bye,
Hannes
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