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[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>
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rwcr authored and Marty Connor committed Jan 20, 2010
1 parent 337e1ed commit b1ba80f
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Showing 4 changed files with 122 additions and 2 deletions.
19 changes: 19 additions & 0 deletions src/include/gpxe/dhcp.h
Expand Up @@ -16,6 +16,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
#include <gpxe/tables.h>
#include <gpxe/uuid.h>
#include <gpxe/netdevice.h>
#include <gpxe/uaccess.h>

struct job_interface;
struct dhcp_options;
Expand Down Expand Up @@ -332,6 +333,16 @@ struct dhcp_netdev_desc {
uint16_t device;
} __attribute__ (( packed ));

/** Use cached network settings
*
* Cached network settings may be available from a prior DHCP request
* (if running as a PXE NBP), non-volatile storage on the NIC, or
* settings set via the command line or an embedded image. If this
* flag is not set, it will be assumed that those sources are
* insufficient and that DHCP should still be run when autobooting.
*/
#define DHCP_EB_USE_CACHED DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 0xb2 )

/** BIOS drive number
*
* This is the drive number for a drive emulated via INT 13. 0x80 is
Expand Down Expand Up @@ -615,4 +626,12 @@ extern int start_dhcp ( struct job_interface *job, struct net_device *netdev );
extern int start_pxebs ( struct job_interface *job, struct net_device *netdev,
unsigned int pxe_type );

/* In environments that can provide cached DHCP packets, this function
* should look for such a packet and call store_cached_dhcpack() with
* it if it exists.
*/
__weak_decl ( void, get_cached_dhcpack, ( void ), (), );

extern void store_cached_dhcpack ( userptr_t data, size_t len );

#endif /* _GPXE_DHCP_H */
76 changes: 76 additions & 0 deletions 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" );
}
22 changes: 21 additions & 1 deletion src/net/udp/dhcp.c
Expand Up @@ -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
*
Expand Down Expand Up @@ -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 )
Expand Down
7 changes: 6 additions & 1 deletion src/usr/dhcpmgmt.c
Expand Up @@ -55,8 +55,13 @@ int dhcp ( struct net_device *netdev ) {
printf ( "DHCP (%s ", netdev->name );
while ( hlen-- )
printf ( "%02x%c", *(chaddr++), ( hlen ? ':' : ')' ) );
if ( ( rc = start_dhcp ( &monojob, netdev ) ) == 0 )

if ( ( rc = start_dhcp ( &monojob, netdev ) ) == 0 ) {
rc = monojob_wait ( "" );
} else if ( rc > 0 ) {
printf ( " using cached\n" );
rc = 0;
}

return rc;
}
Expand Down

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