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Diffstat (limited to 'Documentation/networking/packet_mmap.txt')
| -rw-r--r-- | Documentation/networking/packet_mmap.txt | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt index 1c08a4b0981..7cd879eba5d 100644 --- a/Documentation/networking/packet_mmap.txt +++ b/Documentation/networking/packet_mmap.txt @@ -163,6 +163,19 @@ As capture, each frame contains two parts: A complete tutorial is available at: http://wiki.gnu-log.net/ +By default, the user should put data at : + frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll) + +So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW), +the beginning of the user data will be at : + frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr)) + +If you wish to put user data at a custom offset from the beginning of +the frame (for payload alignment with SOCK_RAW mode for instance) you +can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order +to make this work it must be enabled previously with setsockopt() +and the PACKET_TX_HAS_OFF option. + -------------------------------------------------------------------------------- + PACKET_MMAP settings -------------------------------------------------------------------------------- |