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[dhcp] Honor PXEBS_SKIP option in discovery control

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It is permissible for a DHCP packet containing PXE options to specify
only "discovery control", instead of the more typical boot menu +
prompt options. This is the strategy used by older versions of
dnsmasq; by specifying the discovery control as PXEBS_SKIP, they cause
vendor PXE ROMs to ignore boot server discovery and just use the
filename and next-server options in the initial (Proxy)DHCP packet.
Modify iPXE to accept this behavior, to be more compatible with the
Intel firmware.

Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Tested-by: Kyle Kienapfel <kyle@shadowmage.org>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Joshua Oreman 2010-05-25 16:17:40 -04:00 committed by Michael Brown
parent 723cfad316
commit 620b98ee4b
1 changed files with 26 additions and 2 deletions
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28
src/net/udp/dhcp.c
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@ -401,6 +401,7 @@ static void dhcp_rx_offer ( struct dhcp_session *dhcp,
int has_pxeclient;
int pxeopts_len;
int has_pxeopts;
uint8_t discovery_control = 0;
struct dhcp_offer *offer;
int i;
@ -439,9 +440,32 @@ static void dhcp_rx_offer ( struct dhcp_session *dhcp,
has_pxeclient = ( ( vci_len >= ( int ) sizeof ( vci ) ) &&
( strncmp ( "PXEClient", vci, sizeof (vci) ) == 0 ));
/* Identify presence of PXE-specific options */
/*
* Identify presence of PXE-specific options
*
* The Intel firmware appears to check for:
* - PXE_DISCOVERY_CONTROL exists and has bit 3 set, or
* - both PXE_BOOT_MENU and PXE_BOOT_MENU_PROMPT exist
*
* If DISCOVERY_CONTROL bit 3 is set, the firmware treats this
* packet like a "normal" non-PXE DHCP packet with respect to
* boot filename, except that it can come from ProxyDHCP. This
* is the scheme that dnsmasq uses in the simple case.
*
* Otherwise, if one of the boot menu / boot menu prompt
* options exists but not both, the firmware signals an
* error. If neither exists, the packet is not considered to
* contain DHCP options.
*
* In an effort to preserve semantics but be more flexible, we
* check only for bit 3 of DISCOVERY_CONTROL or the presence
* of BOOT_MENU. We don't care (yet) about the menu prompt.
*/
pxeopts_len = dhcppkt_fetch ( dhcppkt, DHCP_PXE_BOOT_MENU, NULL, 0 );
has_pxeopts = ( pxeopts_len >= 0 );
dhcppkt_fetch ( dhcppkt, DHCP_PXE_DISCOVERY_CONTROL,
&discovery_control, sizeof ( discovery_control ) );
has_pxeopts = ( ( pxeopts_len >= 0 ) ||
( discovery_control & PXEBS_SKIP ) );
if ( has_pxeclient )
DBGC ( dhcp, "%s", ( has_pxeopts ? " pxe" : " proxy" ) );