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[ipv4] Include network device metadata in packet traces

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(Ab)use the "ident" field in transmitted IPv4 packets to convey
metadata about the network device.  In particular:

    bits 0-3 represent the low bits of the "RX" good packet counter
    bits 4-7 represent the low bits of the "RXE" bad packet counter
    bits 8-15 represent the transmitted packet sequence number

This allows some relevant information about the internal state of the
network device to be read out from a packet trace from a non-debug
build of iPXE.  In particular, it allows a packet trace containing
packets transmitted by iPXE to indicate whether or not any packets
have been received by iPXE.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2011-05-05 18:02:44 +01:00
parent e58e4238b6
commit c1cc769ef4
1 changed files with 10 additions and 3 deletions
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13
src/net/ipv4.c
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@ -23,8 +23,8 @@
FILE_LICENCE ( GPL2_OR_LATER );
/* Unique IP datagram identification number */
static uint16_t next_ident = 0;
/* Unique IP datagram identification number (high byte) */
static uint8_t next_ident_high = 0;
/** List of IPv4 miniroutes */
struct list_head ipv4_miniroutes = LIST_HEAD_INIT ( ipv4_miniroutes );
@ -314,7 +314,6 @@ static int ipv4_tx ( struct io_buffer *iobuf,
iphdr->verhdrlen = ( IP_VER | ( sizeof ( *iphdr ) / 4 ) );
iphdr->service = IP_TOS;
iphdr->len = htons ( iob_len ( iobuf ) );
iphdr->ident = htons ( ++next_ident );
iphdr->ttl = IP_TTL;
iphdr->protocol = tcpip_protocol->tcpip_proto;
iphdr->dest = sin_dest->sin_addr;
@ -335,6 +334,14 @@ static int ipv4_tx ( struct io_buffer *iobuf,
goto err;
}
/* (Ab)use the "ident" field to convey metadata about the
* network device statistics into packet traces. Useful for
* extracting debug information from non-debug builds.
*/
iphdr->ident = htons ( ( (++next_ident_high) << 8 ) |
( ( netdev->rx_stats.bad & 0xf ) << 4 ) |
( ( netdev->rx_stats.good & 0xf ) << 0 ) );
/* Determine link-layer destination address */
if ( ( rc = ipv4_ll_addr ( next_hop, iphdr->src, netdev,
ll_dest ) ) != 0 ) {