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Diffstat (limited to 'Documentation/networking/packet_mmap.txt')
| -rw-r--r-- | Documentation/networking/packet_mmap.txt | 42 |
1 files changed, 34 insertions, 8 deletions
diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt index a22fd85e3796..073894d1c093 100644 --- a/Documentation/networking/packet_mmap.txt +++ b/Documentation/networking/packet_mmap.txt @@ -2,13 +2,13 @@ + ABSTRACT -------------------------------------------------------------------------------- -This file documents the CONFIG_PACKET_MMAP option available with the PACKET +This file documents the mmap() facility available with the PACKET socket interface on 2.4 and 2.6 kernels. This type of sockets is used for capture network traffic with utilities like tcpdump or any other that needs raw access to network interface. You can find the latest version of this document at: - http://pusa.uv.es/~ulisses/packet_mmap/ + http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap Howto can be found at: http://wiki.gnu-log.net (packet_mmap) @@ -44,7 +44,7 @@ enabled. For transmission, check the MTU (Maximum Transmission Unit) used and supported by devices of your network. -------------------------------------------------------------------------------- -+ How to use CONFIG_PACKET_MMAP to improve capture process ++ How to use mmap() to improve capture process -------------------------------------------------------------------------------- From the user standpoint, you should use the higher level libpcap library, which @@ -56,7 +56,7 @@ support for PACKET_MMAP, and also probably the libpcap included in your distribu I'm aware of two implementations of PACKET_MMAP in libpcap: - http://pusa.uv.es/~ulisses/packet_mmap/ (by Simon Patarin, based on libpcap 0.6.2) + http://wiki.ipxwarzone.com/ (by Simon Patarin, based on libpcap 0.6.2) http://public.lanl.gov/cpw/ (by Phil Wood, based on lastest libpcap) The rest of this document is intended for people who want to understand @@ -64,7 +64,7 @@ the low level details or want to improve libpcap by including PACKET_MMAP support. -------------------------------------------------------------------------------- -+ How to use CONFIG_PACKET_MMAP directly to improve capture process ++ How to use mmap() directly to improve capture process -------------------------------------------------------------------------------- From the system calls stand point, the use of PACKET_MMAP involves @@ -100,12 +100,12 @@ by the kernel. The destruction of the socket and all associated resources is done by a simple call to close(fd). -Next I will describe PACKET_MMAP settings and it's constraints, +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. -------------------------------------------------------------------------------- -+ How to use CONFIG_PACKET_MMAP directly to improve transmission process ++ How to use mmap() directly to improve transmission process -------------------------------------------------------------------------------- Transmission process is similar to capture as shown below. @@ -432,7 +432,7 @@ TP_STATUS_LOSING : indicates there were packet drops from last time the PACKET_STATISTICS option. TP_STATUS_CSUMNOTREADY: currently it's used for outgoing IP packets which - it's checksum will be done in hardware. So while + its checksum will be done in hardware. So while reading the packet we should not try to check the checksum. @@ -493,6 +493,32 @@ The user can also use poll() to check if a buffer is available: pfd.events = POLLOUT; retval = poll(&pfd, 1, timeout); +------------------------------------------------------------------------------- ++ PACKET_TIMESTAMP +------------------------------------------------------------------------------- + +The PACKET_TIMESTAMP setting determines the source of the timestamp in +the packet meta information. If your NIC is capable of timestamping +packets in hardware, you can request those hardware timestamps to used. +Note: you may need to enable the generation of hardware timestamps with +SIOCSHWTSTAMP. + +PACKET_TIMESTAMP accepts the same integer bit field as +SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE +and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by +PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over +SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set. + + int req = 0; + req |= SOF_TIMESTAMPING_SYS_HARDWARE; + setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req)) + +If PACKET_TIMESTAMP is not set, a software timestamp generated inside +the networking stack is used (the behavior before this setting was added). + +See include/linux/net_tstamp.h and Documentation/networking/timestamping +for more information on hardware timestamps. + -------------------------------------------------------------------------------- + THANKS -------------------------------------------------------------------------------- |