From mboxrd@z Thu Jan 1 00:00:00 1970 From: Norbert van Bolhuis Subject: [PATCH net-next v2] packet: doc: how to PACKET_MMAP with one packet socket for rx and tx Date: Wed, 08 Jan 2014 15:46:44 +0100 Message-ID: <52CD64D4.5020005@aimvalley.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Daniel Borkmann To: netdev@vger.kernel.org Return-path: Received: from mika.eatserver.nl ([195.20.9.75]:52801 "EHLO mika.eatserver.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756510AbaAHOqt (ORCPT ); Wed, 8 Jan 2014 09:46:49 -0500 Sender: netdev-owner@vger.kernel.org List-ID: 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 | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt index 723bf3d..5566c20 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 +419,19 @@ 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: + + ... + 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. + 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