[dhcp] Allow pseudo-DHCP servers to use pseudo-identifiers

Some ProxyDHCP servers and PXE boot servers do not specify a DHCP
server identifier via option 54.  We currently work around this in a
variety of ad-hoc ways:

 - if a ProxyDHCPACK has no server identifier then we treat it as
   having the correct server identifier,

 - if a boot server ACK has no server identifier then we use the
   packet's source IP address as the server identifier.

Introduce the concept of a DHCP server pseudo-identifier, defined as
being:

 - the server identifier (option 54), or

 - if there is no server identifier, then the next-server address
   (siaddr),

 - if there is no server identifier or next-server address, then the
   DHCP packet's source IP address.

Use the pseudo-identifier in place of the server identifier when
handling ProxyDHCP and PXE boot server responses.

Originally-fixed-by: Wissam Shoukair <wissams@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/udp/dhcp.c

 	 * @v dhcppkt		DHCP packet
 	 * @v peer		Destination address
 	 */
-	int ( * tx ) ( struct dhcp_session *dhcp,
-		       struct dhcp_packet *dhcppkt,
+	int ( * tx ) ( struct dhcp_session *dhcp, struct dhcp_packet *dhcppkt,
 		       struct sockaddr_in *peer );
-	/** Handle received packet
+	/**
+	 * Handle received packet
 	 *
 	 * @v dhcp		DHCP session
 	 * @v dhcppkt		DHCP packet
 	 * @v peer		DHCP server address
 	 * @v msgtype		DHCP message type
 	 * @v server_id		DHCP server ID
+	 * @v pseudo_id		DHCP server pseudo-ID
 	 */
-	void ( * rx ) ( struct dhcp_session *dhcp,
-			struct dhcp_packet *dhcppkt,
-			struct sockaddr_in *peer,
-			uint8_t msgtype, struct in_addr server_id );
-	/** Handle timer expiry
+	void ( * rx ) ( struct dhcp_session *dhcp, struct dhcp_packet *dhcppkt,
+			struct sockaddr_in *peer, uint8_t msgtype,
+			struct in_addr server_id, struct in_addr pseudo_id );
+	/**
+	 * Handle timer expiry
 	 *
 	 * @v dhcp		DHCP session
 	 */
  * @v peer		DHCP server address
  * @v msgtype		DHCP message type
  * @v server_id		DHCP server ID
+ * @v pseudo_id		DHCP server pseudo-ID
  */
 static void dhcp_discovery_rx ( struct dhcp_session *dhcp,
 				struct dhcp_packet *dhcppkt,
 				struct sockaddr_in *peer, uint8_t msgtype,
-				struct in_addr server_id ) {
+				struct in_addr server_id,
+				struct in_addr pseudo_id ) {
 	struct in_addr ip;
 	char vci[9]; /* "PXEClient" */
 	int vci_len;
 	DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
 	       dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
 	       ntohs ( peer->sin_port ) );
-	if ( server_id.s_addr != peer->sin_addr.s_addr )
-		DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
+	if ( ( server_id.s_addr != peer->sin_addr.s_addr ) ||
+	     ( pseudo_id.s_addr != peer->sin_addr.s_addr ) ) {
+		DBGC ( dhcp, " (%s/", inet_ntoa ( server_id ) );
+		DBGC ( dhcp, "%s)", inet_ntoa ( pseudo_id ) );
+	}
 
 	/* Identify offered IP address */
 	ip = dhcppkt->dhcphdr->yiaddr;
 	}
 
 	/* Select as ProxyDHCP offer, if applicable */
-	if ( server_id.s_addr && has_pxeclient &&
+	if ( pseudo_id.s_addr && has_pxeclient &&
 	     ( priority >= dhcp->proxy_priority ) ) {
 		dhcppkt_put ( dhcp->proxy_offer );
-		dhcp->proxy_server = server_id;
+		dhcp->proxy_server = pseudo_id;
 		dhcp->proxy_offer = dhcppkt_get ( dhcppkt );
 		dhcp->proxy_priority = priority;
 	}
  * @v peer		DHCP server address
  * @v msgtype		DHCP message type
  * @v server_id		DHCP server ID
+ * @v pseudo_id		DHCP server pseudo-ID
  */
 static void dhcp_request_rx ( struct dhcp_session *dhcp,
 			      struct dhcp_packet *dhcppkt,
 			      struct sockaddr_in *peer, uint8_t msgtype,
-			      struct in_addr server_id ) {
+			      struct in_addr server_id,
+			      struct in_addr pseudo_id ) {
 	struct in_addr ip;
 	struct settings *parent;
 	struct settings *settings;
 	DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
 	       dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
 	       ntohs ( peer->sin_port ) );
-	if ( server_id.s_addr != peer->sin_addr.s_addr )
-		DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
+	if ( ( server_id.s_addr != peer->sin_addr.s_addr ) ||
+	     ( pseudo_id.s_addr != peer->sin_addr.s_addr ) ) {
+		DBGC ( dhcp, " (%s/", inet_ntoa ( server_id ) );
+		DBGC ( dhcp, "%s)", inet_ntoa ( pseudo_id ) );
+	}
 
 	/* Identify leased IP address */
 	ip = dhcppkt->dhcphdr->yiaddr;
  * @v peer		DHCP server address
  * @v msgtype		DHCP message type
  * @v server_id		DHCP server ID
+ * @v pseudo_id		DHCP server pseudo-ID
  */
 static void dhcp_proxy_rx ( struct dhcp_session *dhcp,
 			    struct dhcp_packet *dhcppkt,
 			    struct sockaddr_in *peer, uint8_t msgtype,
-			    struct in_addr server_id ) {
+			    struct in_addr server_id,
+			    struct in_addr pseudo_id ) {
 	struct settings *settings = &dhcppkt->settings;
 	int rc;
 
 	DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
 	       dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
 	       ntohs ( peer->sin_port ) );
-	if ( server_id.s_addr != peer->sin_addr.s_addr )
-		DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
+	if ( ( server_id.s_addr != peer->sin_addr.s_addr ) ||
+	     ( pseudo_id.s_addr != peer->sin_addr.s_addr ) ) {
+		DBGC ( dhcp, " (%s/", inet_ntoa ( server_id ) );
+		DBGC ( dhcp, "%s)", inet_ntoa ( pseudo_id ) );
+	}
 	DBGC ( dhcp, "\n" );
 
 	/* Filter out unacceptable responses */
 		return;
 	if ( ( msgtype != DHCPOFFER ) && ( msgtype != DHCPACK ) )
 		return;
-	if ( server_id.s_addr /* Linux PXE server omits server ID */ &&
-	     ( server_id.s_addr != dhcp->proxy_server.s_addr ) )
+	if ( ( pseudo_id.s_addr != dhcp->proxy_server.s_addr ) )
 		return;
 
 	/* Register settings */
  * @v peer		DHCP server address
  * @v msgtype		DHCP message type
  * @v server_id		DHCP server ID
+ * @v pseudo_id		DHCP server pseudo-ID
  */
 static void dhcp_pxebs_rx ( struct dhcp_session *dhcp,
 			    struct dhcp_packet *dhcppkt,
 			    struct sockaddr_in *peer, uint8_t msgtype,
-			    struct in_addr server_id ) {
+			    struct in_addr server_id,
+			    struct in_addr pseudo_id ) {
 	struct dhcp_pxe_boot_menu_item menu_item = { 0, 0 };
 	int rc;
 
 	DBGC ( dhcp, "DHCP %p %s from %s:%d", dhcp,
 	       dhcp_msgtype_name ( msgtype ), inet_ntoa ( peer->sin_addr ),
 	       ntohs ( peer->sin_port ) );
-	if ( server_id.s_addr != peer->sin_addr.s_addr )
-		DBGC ( dhcp, " (%s)", inet_ntoa ( server_id ) );
+	if ( ( server_id.s_addr != peer->sin_addr.s_addr ) ||
+	     ( pseudo_id.s_addr != peer->sin_addr.s_addr ) ) {
+		DBGC ( dhcp, " (%s/", inet_ntoa ( server_id ) );
+		DBGC ( dhcp, "%s)", inet_ntoa ( pseudo_id ) );
+	}
 
 	/* Identify boot menu item */
 	dhcppkt_fetch ( dhcppkt, DHCP_PXE_BOOT_MENU_ITEM,
 		return;
 	if ( menu_item.type != dhcp->pxe_type )
 		return;
-	if ( ! dhcp_pxebs_accept ( dhcp, ( server_id.s_addr ?
-					   server_id : peer->sin_addr ) ) )
+	if ( ! dhcp_pxebs_accept ( dhcp, pseudo_id ) )
 		return;
 
 	/* Register settings */
 	struct dhcphdr *dhcphdr;
 	uint8_t msgtype = 0;
 	struct in_addr server_id = { 0 };
+	struct in_addr pseudo_id;
 	int rc = 0;
 
 	/* Sanity checks */
 	dhcppkt_fetch ( dhcppkt, DHCP_SERVER_IDENTIFIER,
 			&server_id, sizeof ( server_id ) );
 
+	/* Identify server pseudo-ID */
+	pseudo_id = server_id;
+	if ( ! pseudo_id.s_addr )
+		pseudo_id = dhcppkt->dhcphdr->siaddr;
+	if ( ! pseudo_id.s_addr )
+		pseudo_id = peer->sin_addr;
+
 	/* Check for matching transaction ID */
 	if ( dhcphdr->xid != dhcp->xid ) {
 		DBGC ( dhcp, "DHCP %p %s from %s:%d has bad transaction "
 	}
 
 	/* Handle packet based on current state */
-	dhcp->state->rx ( dhcp, dhcppkt, peer, msgtype, server_id );
+	dhcp->state->rx ( dhcp, dhcppkt, peer, msgtype, server_id, pseudo_id );
 
  err_chaddr:
  err_xid: