diff options
Diffstat (limited to 'src/net/ethernet.c')
| -rw-r--r-- | src/net/ethernet.c | 38 |
1 files changed, 36 insertions, 2 deletions
diff --git a/src/net/ethernet.c b/src/net/ethernet.c index 33e05725..6ddf0534 100644 --- a/src/net/ethernet.c +++ b/src/net/ethernet.c @@ -47,6 +47,24 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); uint8_t eth_broadcast[ETH_ALEN] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff }; /** + * Check if Ethernet packet has an 802.3 LLC header + * + * @v ethhdr Ethernet header + * @ret is_llc Packet has 802.3 LLC header + */ +static inline int eth_is_llc_packet ( struct ethhdr *ethhdr ) { + uint8_t len_msb; + + /* Check if the protocol field contains a value short enough + * to be a frame length. The slightly convoluted form of the + * comparison is designed to reduce to a single x86 + * instruction. + */ + len_msb = *( ( uint8_t * ) ðhdr->h_protocol ); + return ( len_msb < 0x06 ); +} + +/** * Add Ethernet link-layer header * * @v netdev Network device @@ -84,9 +102,14 @@ int eth_pull ( struct net_device *netdev __unused, struct io_buffer *iobuf, const void **ll_dest, const void **ll_source, uint16_t *net_proto, unsigned int *flags ) { struct ethhdr *ethhdr = iobuf->data; + uint16_t *llc_proto; - /* Sanity check */ - if ( iob_len ( iobuf ) < sizeof ( *ethhdr ) ) { + /* Sanity check. While in theory we could receive a one-byte + * packet, this will never happen in practice and performing + * the combined length check here avoids the need for an + * additional comparison if we detect an LLC frame. + */ + if ( iob_len ( iobuf ) < ( sizeof ( *ethhdr ) + sizeof ( *llc_proto ))){ DBG ( "Ethernet packet too short (%zd bytes)\n", iob_len ( iobuf ) ); return -EINVAL; @@ -104,6 +127,17 @@ int eth_pull ( struct net_device *netdev __unused, struct io_buffer *iobuf, ( is_broadcast_ether_addr ( ethhdr->h_dest ) ? LL_BROADCAST : 0 ) ); + /* If this is an LLC frame (with a length in place of the + * protocol field), then use the next two bytes (which happen + * to be the LLC DSAP and SSAP) as the protocol. This allows + * for minimal-overhead support for receiving (rare) LLC + * frames, without requiring a full LLC protocol layer. + */ + if ( eth_is_llc_packet ( ethhdr ) ) { + llc_proto = ( ðhdr->h_protocol + 1 ); + *net_proto = *llc_proto; + } + return 0; } |