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[dhcp] Add generic facility for using cached network settings

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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>
This commit is contained in:
Joshua Oreman
2009-12-08 03:40:50 -05:00
committed by Marty Connor
parent 337e1ed4b4
commit b1ba80f8fb
4 changed files with 122 additions and 2 deletions
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22
src/net/udp/dhcp.c
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@@ -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 )