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[dhcp] Include session state metadata in packet traces 

(Ab)use the "secs" field in transmitted DHCP packets to convey
metadata about the DHCP session state.  In particular:

  bit 0 represents the receipt of a ProxyDHCPOFFER
  bit 1 represents the receipt of a DHCPOFFER
  bits 2+ represent the transmitted packet sequence number

This allows some relevant information about the internal state of the
DHCP session to be read out from a packet trace from a non-debug build
of iPXE.  It also potentially allows replies to be correlated to their
requests (for servers that copy the "secs" field from request to
reply).

Signed-off-by: Michael Brown <mcb30@ipxe.org>
pull/1/head
Michael Brown 2010-10-09 01:24:18 +01:00
parent 831106a875
commit 6d11229e83
1 changed files with 10 additions and 0 deletions
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10
src/net/udp/dhcp.c
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@ -245,6 +245,8 @@ struct dhcp_session {
/** Retransmission timer */ /** Retransmission timer */
struct retry_timer timer; struct retry_timer timer;
/** Transmission counter */
unsigned int count;
/** Start time of the current state (in ticks) */ /** Start time of the current state (in ticks) */
unsigned long start; unsigned long start;
}; };
@ -1098,6 +1100,14 @@ static int dhcp_tx ( struct dhcp_session *dhcp ) {
goto done; goto done;
} }
/* (Ab)use the "secs" field to convey metadata about the DHCP
* session state into packet traces. Useful for extracting
* debug information from non-debug builds.
*/
dhcppkt.dhcphdr->secs = htons ( ( ++(dhcp->count) << 2 ) |
( dhcp->offer.s_addr ? 0x02 : 0 ) |
( dhcp->proxy_offer ? 0x01 : 0 ) );
/* Fill in packet based on current state */ /* Fill in packet based on current state */
if ( ( rc = dhcp->state->tx ( dhcp, &dhcppkt, &peer ) ) != 0 ) { if ( ( rc = dhcp->state->tx ( dhcp, &dhcppkt, &peer ) ) != 0 ) {
DBGC ( dhcp, "DHCP %p could not fill DHCP request: %s\n", DBGC ( dhcp, "DHCP %p could not fill DHCP request: %s\n",