[dhcp] Add generic facility for using cached network settings

When a DHCP session is started (using autoboot or a command-line `dhcp
net0'), check whether the new setting use-cached (DHCP option 175.178)
is TRUE; if so, skip DHCP and rely on currently registered
settings. This lets one combine a static IP with autoboot.

Before checking the use-cached setting, call a weak
get_cached_dhcpack() hook that can be implemented by particular builds
of gPXE supporting some fashion of retrieving a cached DHCPACK packet.
If one is available, it is registered as an options source, and then
either that packet's option 175.178 or the user's prior manual
use-cached setting can allow skipping duplicate DHCP.

Using cached packets is not the default because DHCP servers are often
configured to give gPXE different options than they give a vendor PXE
client; in order to break the infinite loop of PXE chaining, one would
need to load a gPXE with an embedded image that does something more
than autoboot.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/net/cachedhcp.c

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2009 Joshua Oreman <oremanj@rwcr.net>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <gpxe/dhcp.h>
+#include <gpxe/dhcppkt.h>
+#include <gpxe/netdevice.h>
+#include <gpxe/iobuf.h>
+#include <gpxe/uaccess.h>
+
+/** @file
+ *
+ * Cached DHCP packet handling
+ *
+ */
+
+/**
+ * Store cached DHCPACK packet
+ *
+ * @v data		User pointer to cached DHCP packet data
+ * @v len		Length of cached DHCP packet data
+ * @ret rc		Return status code
+ *
+ * This function should be called by the architecture-specific
+ * get_cached_dhcpack() handler.
+ */
+void store_cached_dhcpack ( userptr_t data, size_t len ) {
+	struct dhcp_packet *dhcppkt;
+	struct dhcphdr *dhcphdr;
+	struct settings *parent;
+	int rc;
+
+	/* Create DHCP packet */
+	dhcppkt = zalloc ( sizeof ( *dhcppkt ) + len );
+	if ( ! dhcppkt )
+		return;
+
+	/* Fill in data for DHCP packet */
+	dhcphdr = ( ( ( void * ) dhcppkt ) + sizeof ( * dhcppkt ) );
+	copy_from_user ( dhcphdr, data, 0, len );
+	dhcppkt_init ( dhcppkt, dhcphdr, len );
+	DBG_HD ( dhcppkt->options.data, dhcppkt->options.len );
+
+	/* Register settings on the last opened network device.
+	 * This will have the effect of registering cached settings
+	 * with a network device when "dhcp netX" is performed for that
+	 * device, which is usually what we want.
+	 */
+	parent = netdev_settings ( last_opened_netdev() );
+	if ( ( rc = register_settings ( &dhcppkt->settings, parent ) ) != 0 )
+		DBG ( "DHCP could not register cached settings: %s\n",
+		      strerror ( rc ) );
+
+	dhcppkt_put ( dhcppkt );
+
+	DBG ( "DHCP registered cached settings\n" );
+}

src/net/udp/dhcp.c

@@ -110,6 +110,14 @@ struct setting user_class_setting __setting = {
 	.type = &setting_type_string,
 };
 
+/** Use cached network settings */
+struct setting use_cached_setting __setting = {
+	.name = "use-cached",
+	.description = "Use cached network settings",
+	.tag = DHCP_EB_USE_CACHED,
+	.type = &setting_type_uint8,
+};
+
 /**
  * Name a DHCP packet type
  *
@@ -1237,16 +1245,28 @@ static struct sockaddr dhcp_peer = {
  *
  * @v job		Job control interface
  * @v netdev		Network device
- * @ret rc		Return status code
+ * @ret rc		Return status code, or positive if cached
  *
  * Starts DHCP on the specified network device.  If successful, the
  * DHCPACK (and ProxyDHCPACK, if applicable) will be registered as
  * option sources.
+ *
+ * On a return of 0, a background job has been started to perform the
+ * DHCP request. Any nonzero return means the job has not been
+ * started; a positive return value indicates the success condition of
+ * having fetched the appropriate data from cached information.
  */
 int start_dhcp ( struct job_interface *job, struct net_device *netdev ) {
 	struct dhcp_session *dhcp;
 	int rc;
 
+	/* Check for cached DHCP information */
+	get_cached_dhcpack();
+	if ( fetch_uintz_setting ( NULL, &use_cached_setting ) ) {
+		DBG ( "DHCP using cached network settings\n" );
+		return 1;
+	}
+
 	/* Allocate and initialise structure */
 	dhcp = zalloc ( sizeof ( *dhcp ) );
 	if ( ! dhcp )