netdev - Re: [PATCH 1/1] af_packet: don't enable timestamps in mmap'ed sockets

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Date:	Thu, 09 Aug 2007 20:44:21 +0200
From:	Unai Uribarri <unai.uribarri@...enet.com>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] af_packet: don't enable timestamps in mmap'ed
	sockets

There is another option:

1. Move timestampt activation to packet_set_ring(), so it's activated
only once at setup instead of every time a packet arrives.
2. Fix sock_setsockopt() so setting SO_TIMESTAMP to 0 effectively
disables timestamp.

My first patch set did that. I sent that patches in mime multipart
format and they were removed from the list archives. I can resent them
in plain text if needed.


On jue, 2007-08-09 at 22:18 +0400, Evgeniy Polyakov wrote:
> On Thu, Aug 09, 2007 at 08:13:54PM +0200, Unai Uribarri (unai.uribarri@...enet.com) wrote:
> > On jue, 2007-08-09 at 18:33 +0400, Evgeniy Polyakov wrote:
> > > On Thu, Aug 09, 2007 at 04:21:54PM +0200, Unai Uribarri (unai.uribarri@...enet.com) wrote:
> > > > The attached patch removes the automatic timestamp activation, that
> > > > only mmap'ed AF_PACKET sockets perform. I known it can break user
> > > > applications, but I believe that it's the correct solution.
> > > 
> > > How tcpdump with mmap libpcap will work with it?
> > 
> > In Linux, you can enable timestamps on any socket executing:
> > 
> > int val = 1;
> > setsockopt(sock, SOL_SOCKET, SO_TIMESTAMP, &val, sizeof(val));
> > 
> > PD: Current release of tcpdump doesn't mmap the reception ring and
> > timestamps packets at user space with gettimeofday. It isn't the best
> > performing alternative, but it's portable.
>  
> IIRC, there was/is a libpcap which worked with mapped sockets, mybe not 
> official though. Any application which depened on having timestamps with
> packets will not work now. Why not to implement an
> absolutely_turn_off_timestamps option instead of breaking compatibility?
> 


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