From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH net-next] packet: doc: how to PACKET_MMAP with one packet socket for rx and tx Date: Wed, 08 Jan 2014 15:29:38 +0100 Message-ID: <52CD60D2.5040608@redhat.com> References: <52CD5F44.2090307@aimvalley.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Norbert van Bolhuis Return-path: Received: from mx1.redhat.com ([209.132.183.28]:38960 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755121AbaAHO3n (ORCPT ); Wed, 8 Jan 2014 09:29:43 -0500 In-Reply-To: <52CD5F44.2090307@aimvalley.nl> Sender: netdev-owner@vger.kernel.org List-ID: On 01/08/2014 03:23 PM, Norbert van Bolhuis wrote: > > Describe how to use one AF_PACKET socket for rx and tx. > > Cc: Daniel Borkmann > Signed-off-by: Norbert van Bolhuis > --- > Documentation/networking/packet_mmap.txt | 14 ++++++++++++++ > 1 files changed, 14 insertions(+), 0 deletions(-) > > diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt > index 723bf3d..2503a5a 100644 > --- a/Documentation/networking/packet_mmap.txt > +++ b/Documentation/networking/packet_mmap.txt > @@ -98,6 +98,11 @@ by the kernel. > The destruction of the socket and all associated resources > is done by a simple call to close(fd). > > +As without PACKET_MMAP, it is possible to use one socket for > +capture and transmission. This can be done by mapping the > +allocated RX and TX buffer ring with a single mmap() call. See > +"Mapping and use of the circular buffer (ring)". > + > Next I will describe PACKET_MMAP settings and its constraints, > also the mapping of the circular buffer in the user process and > the use of this buffer. > @@ -414,6 +419,15 @@ tp_block_size/tp_frame_size frames there will be a gap between > the frames. This is because a frame cannot be spawn across two > blocks. > > +To use one socket for capture and transmission, the mapping of both the RX > +and TX buffer ring has to be done with one call to mmap: As this caused some confusion in the past for some people, it would be great to mention here in this example also: ... setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &foo, sizeof(foo)); setsockopt(fd, SOL_PACKET, PACKET_TX_RING, &bar, sizeof(bar)); ... > + rx_ring = mmap(0, size * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); > + tx_ring = rx_ring + size; > + > +RX must be the first as the kernel maps the TX ring memory right after > +the RX one. Otherwise looks perfect! > At the beginning of each frame there is an status field (see > struct tpacket_hdr). If this field is 0 means that the frame is ready > to be used for the kernel, If not, there is a frame the user can read