diff options
| author | Norbert van Bolhuis <nvbolhuis@aimvalley.nl> | 2014-01-10 10:22:37 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-01-13 14:45:59 -0800 |
| commit | 7e11daa7c19ec319fa4b750fd249a18957f17797 (patch) | |
| tree | 57227f64774c356c4643e35d4de97faddb34217b | |
| parent | 6daaf0de2f3170206f57e7881adfbd8682cdd7fb (diff) | |
packet: doc: describe PACKET_MMAP with one packet socket for rx and tx
Document how to use one AF_PACKET mmap socket for RX and TX.
Signed-off-by: Norbert van Bolhuis <nvbolhuis@aimvalley.nl>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | 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 723bf3d33a6e..91ffe1d9e8ca 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). +Similarly 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 |