diff options
Diffstat (limited to 'net/packet/af_packet.c')
| -rw-r--r-- | net/packet/af_packet.c | 40 |
1 files changed, 22 insertions, 18 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index af6c93ed9fa0..cefbd50c1090 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -93,52 +93,56 @@ /* Assumptions: - - if device has no dev->hard_header routine, it adds and removes ll header - inside itself. In this case ll header is invisible outside of device, - but higher levels still should reserve dev->hard_header_len. - Some devices are enough clever to reallocate skb, when header - will not fit to reserved space (tunnel), another ones are silly - (PPP). + - If the device has no dev->header_ops, there is no LL header visible + above the device. In this case, its hard_header_len should be 0. + The device may prepend its own header internally. In this case, its + needed_headroom should be set to the space needed for it to add its + internal header. + For example, a WiFi driver pretending to be an Ethernet driver should + set its hard_header_len to be the Ethernet header length, and set its + needed_headroom to be (the real WiFi header length - the fake Ethernet + header length). - packet socket receives packets with pulled ll header, so that SOCK_RAW should push it back. On receive: ----------- -Incoming, dev->hard_header!=NULL +Incoming, dev->header_ops != NULL mac_header -> ll header data -> data -Outgoing, dev->hard_header!=NULL +Outgoing, dev->header_ops != NULL mac_header -> ll header data -> ll header -Incoming, dev->hard_header==NULL - mac_header -> UNKNOWN position. It is very likely, that it points to ll - header. PPP makes it, that is wrong, because introduce - assymetry between rx and tx paths. +Incoming, dev->header_ops == NULL + mac_header -> data + However drivers often make it point to the ll header. + This is incorrect because the ll header should be invisible to us. data -> data -Outgoing, dev->hard_header==NULL - mac_header -> data. ll header is still not built! +Outgoing, dev->header_ops == NULL + mac_header -> data. ll header is invisible to us. data -> data Resume - If dev->hard_header==NULL we are unlikely to restore sensible ll header. + If dev->header_ops == NULL we are unable to restore the ll header, + because it is invisible to us. On transmit: ------------ -dev->hard_header != NULL +dev->header_ops != NULL mac_header -> ll header data -> ll header -dev->hard_header == NULL (ll header is added by device, we cannot control it) +dev->header_ops == NULL (ll header is invisible to us) mac_header -> data data -> data - We should set nh.raw on output to correct posistion, + We should set network_header on output to the correct position, packet classifier depends on it. */ |