[pxe] Separate parent PXE API caller from UNDINET driver

Calling the parent PXE stack (the stack that loaded us, for
undionly.kkpxe) can be useful for more than UNDI calls; for instance,
it lets us get cached DHCP packets to avoid re-DHCP when working with
embedded images.

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

src/arch/i386/Makefile

 SRCDIRS		+= arch/i386/drivers/net
 SRCDIRS		+= arch/i386/interface/pcbios
 SRCDIRS		+= arch/i386/interface/pxe
+SRCDIRS		+= arch/i386/interface/pxeparent
 SRCDIRS 	+= arch/i386/interface/syslinux
 SRCDIRS		+= arch/i386/hci/commands
 

src/arch/i386/drivers/net/undiisr.S

 	movw	%ax, %ds
 
 	/* Check that we have an UNDI entry point */
-	cmpw	$0, undinet_entry_point
+	cmpw	$0, pxeparent_entry_point
 	je	chain
 	
 	/* Issue UNDI API call */
 	pushw	%es
 	pushw	%di
 	pushw	%bx
-	lcall	*undinet_entry_point
+	lcall	*pxeparent_entry_point
 	cli	/* Just in case */
 	addw	$6, %sp
 	cmpw	$PXENV_UNDI_ISR_OUT_OURS, funcflag

src/arch/i386/drivers/net/undinet.c

 #include <gpxe/ethernet.h>
 #include <undi.h>
 #include <undinet.h>
+#include <pxeparent.h>
 
 
 /** @file
 
 static void undinet_close ( struct net_device *netdev );
 
-/*****************************************************************************
- *
- * UNDI API call
- *
- *****************************************************************************
- */
-
-/**
- * Name UNDI API call
- *
- * @v function		API call number
- * @ret name		API call name
- */
-static inline __attribute__ (( always_inline )) const char *
-undinet_function_name ( unsigned int function ) {
-	switch ( function ) {
-	case PXENV_START_UNDI:
-		return "PXENV_START_UNDI";
-	case PXENV_STOP_UNDI:
-		return "PXENV_STOP_UNDI";
-	case PXENV_UNDI_STARTUP:
-		return "PXENV_UNDI_STARTUP";
-	case PXENV_UNDI_CLEANUP:
-		return "PXENV_UNDI_CLEANUP";
-	case PXENV_UNDI_INITIALIZE:
-		return "PXENV_UNDI_INITIALIZE";
-	case PXENV_UNDI_RESET_ADAPTER:
-		return "PXENV_UNDI_RESET_ADAPTER";
-	case PXENV_UNDI_SHUTDOWN:
-		return "PXENV_UNDI_SHUTDOWN";
-	case PXENV_UNDI_OPEN:
-		return "PXENV_UNDI_OPEN";
-	case PXENV_UNDI_CLOSE:
-		return "PXENV_UNDI_CLOSE";
-	case PXENV_UNDI_TRANSMIT:
-		return "PXENV_UNDI_TRANSMIT";
-	case PXENV_UNDI_SET_MCAST_ADDRESS:
-		return "PXENV_UNDI_SET_MCAST_ADDRESS";
-	case PXENV_UNDI_SET_STATION_ADDRESS:
-		return "PXENV_UNDI_SET_STATION_ADDRESS";
-	case PXENV_UNDI_SET_PACKET_FILTER:
-		return "PXENV_UNDI_SET_PACKET_FILTER";
-	case PXENV_UNDI_GET_INFORMATION:
-		return "PXENV_UNDI_GET_INFORMATION";
-	case PXENV_UNDI_GET_STATISTICS:
-		return "PXENV_UNDI_GET_STATISTICS";
-	case PXENV_UNDI_CLEAR_STATISTICS:
-		return "PXENV_UNDI_CLEAR_STATISTICS";
-	case PXENV_UNDI_INITIATE_DIAGS:
-		return "PXENV_UNDI_INITIATE_DIAGS";
-	case PXENV_UNDI_FORCE_INTERRUPT:
-		return "PXENV_UNDI_FORCE_INTERRUPT";
-	case PXENV_UNDI_GET_MCAST_ADDRESS:
-		return "PXENV_UNDI_GET_MCAST_ADDRESS";
-	case PXENV_UNDI_GET_NIC_TYPE:
-		return "PXENV_UNDI_GET_NIC_TYPE";
-	case PXENV_UNDI_GET_IFACE_INFO:
-		return "PXENV_UNDI_GET_IFACE_INFO";
-	/*
-	 * Duplicate case value; this is a bug in the PXE specification.
-	 *
-	 *	case PXENV_UNDI_GET_STATE:
-	 *		return "PXENV_UNDI_GET_STATE";
-	 */
-	case PXENV_UNDI_ISR:
-		return "PXENV_UNDI_ISR";
-	default:
-		return "UNKNOWN API CALL";
-	}
-}
-
-/**
- * UNDI parameter block
- *
- * Used as the paramter block for all UNDI API calls.  Resides in base
- * memory.
- */
-static union u_PXENV_ANY __bss16 ( undinet_params );
-#define undinet_params __use_data16 ( undinet_params )
-
-/** UNDI entry point
- *
- * Used as the indirection vector for all UNDI API calls.  Resides in
- * base memory.
- */
-SEGOFF16_t __bss16 ( undinet_entry_point );
-#define undinet_entry_point __use_data16 ( undinet_entry_point )
-
-/**
- * Issue UNDI API call
- *
- * @v undinic		UNDI NIC
- * @v function		API call number
- * @v params		UNDI parameter block
- * @v params_len	Length of UNDI parameter block
- * @ret rc		Return status code
- */
-static int undinet_call ( struct undi_nic *undinic, unsigned int function,
-			  void *params, size_t params_len ) {
-	PXENV_EXIT_t exit;
-	int discard_b, discard_D;
-	int rc;
-
-	/* Copy parameter block and entry point */
-	assert ( params_len <= sizeof ( undinet_params ) );
-	memcpy ( &undinet_params, params, params_len );
-
-	/* Call real-mode entry point.  This calling convention will
-	 * work with both the !PXE and the PXENV+ entry points.
-	 */
-	__asm__ __volatile__ ( REAL_CODE ( "pushw %%es\n\t"
-					   "pushw %%di\n\t"
-					   "pushw %%bx\n\t"
-					   "lcall *undinet_entry_point\n\t"
-					   "addw $6, %%sp\n\t" )
-			       : "=a" ( exit ), "=b" ( discard_b ),
-			         "=D" ( discard_D )
-			       : "b" ( function ),
-			         "D" ( __from_data16 ( &undinet_params ) )
-			       : "ecx", "edx", "esi", "ebp" );
-
-	/* UNDI API calls may rudely change the status of A20 and not
-	 * bother to restore it afterwards.  Intel is known to be
-	 * guilty of this.
-	 *
-	 * Note that we will return to this point even if A20 gets
-	 * screwed up by the UNDI driver, because Etherboot always
-	 * resides in an even megabyte of RAM.
-	 */	
-	gateA20_set();
-
-	/* Determine return status code based on PXENV_EXIT and
-	 * PXENV_STATUS
-	 */
-	if ( exit == PXENV_EXIT_SUCCESS ) {
-		rc = 0;
-	} else {
-		rc = -undinet_params.Status;
-		/* Paranoia; don't return success for the combination
-		 * of PXENV_EXIT_FAILURE but PXENV_STATUS_SUCCESS
-		 */
-		if ( rc == 0 )
-			rc = -EIO;
-	}
-
-	/* If anything goes wrong, print as much debug information as
-	 * it's possible to give.
-	 */
-	if ( rc != 0 ) {
-		SEGOFF16_t rm_params = {
-			.segment = rm_ds,
-			.offset = __from_data16 ( &undinet_params ),
-		};
-
-		DBGC ( undinic, "UNDINIC %p %s failed: %s\n", undinic,
-		       undinet_function_name ( function ), strerror ( rc ) );
-		DBGC ( undinic, "UNDINIC %p parameters at %04x:%04x length "
-		       "%#02zx, entry point at %04x:%04x\n", undinic,
-		       rm_params.segment, rm_params.offset, params_len,
-		       undinet_entry_point.segment,
-		       undinet_entry_point.offset );
-		DBGC ( undinic, "UNDINIC %p parameters provided:\n", undinic );
-		DBGC_HDA ( undinic, rm_params, params, params_len );
-		DBGC ( undinic, "UNDINIC %p parameters returned:\n", undinic );
-		DBGC_HDA ( undinic, rm_params, &undinet_params, params_len );
-	}
-
-	/* Copy parameter block back */
-	memcpy ( params, &undinet_params, params_len );
-
-	return rc;
-}
+/** Address of UNDI entry point */
+static SEGOFF16_t undinet_entry;
 
 /*****************************************************************************
  *
  */
 static int undinet_transmit ( struct net_device *netdev,
 			      struct io_buffer *iobuf ) {
-	struct undi_nic *undinic = netdev->priv;
 	struct s_PXENV_UNDI_TRANSMIT undi_transmit;
 	size_t len = iob_len ( iobuf );
 	int rc;
 	undinet_tbd.Xmit.offset = __from_data16 ( basemem_packet );
 
 	/* Issue PXE API call */
-	if ( ( rc = undinet_call ( undinic, PXENV_UNDI_TRANSMIT,
-				   &undi_transmit,
-				   sizeof ( undi_transmit ) ) ) != 0 )
+	if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_TRANSMIT,
+				     &undi_transmit,
+				     sizeof ( undi_transmit ) ) ) != 0 )
 		goto done;
 
 	/* Free I/O buffer */
 
 	/* Run through the ISR loop */
 	while ( 1 ) {
-		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_ISR, &undi_isr,
-					   sizeof ( undi_isr ) ) ) != 0 )
+		if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_ISR,
+					     &undi_isr,
+					     sizeof ( undi_isr ) ) ) != 0 )
 			break;
 		switch ( undi_isr.FuncFlag ) {
 		case PXENV_UNDI_ISR_OUT_TRANSMIT:
 	 */
 	memcpy ( undi_set_address.StationAddress, netdev->ll_addr,
 		 sizeof ( undi_set_address.StationAddress ) );
-	undinet_call ( undinic, PXENV_UNDI_SET_STATION_ADDRESS,
-		       &undi_set_address, sizeof ( undi_set_address ) );
+	pxeparent_call ( undinet_entry, PXENV_UNDI_SET_STATION_ADDRESS,
+			 &undi_set_address, sizeof ( undi_set_address ) );
 
 	/* Open NIC.  We ask for promiscuous operation, since it's the
 	 * only way to ask for all multicast addresses.  On any
 	 */
 	memset ( &undi_open, 0, sizeof ( undi_open ) );
 	undi_open.PktFilter = ( FLTR_DIRECTED | FLTR_BRDCST | FLTR_PRMSCS );
-	if ( ( rc = undinet_call ( undinic, PXENV_UNDI_OPEN, &undi_open,
-				   sizeof ( undi_open ) ) ) != 0 )
+	if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_OPEN,
+				     &undi_open, sizeof ( undi_open ) ) ) != 0 )
 		goto err;
 
 	DBGC ( undinic, "UNDINIC %p opened\n", undinic );
 	/* Ensure ISR has exited cleanly */
 	while ( undinic->isr_processing ) {
 		undi_isr.FuncFlag = PXENV_UNDI_ISR_IN_GET_NEXT;
-		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_ISR, &undi_isr,
-					   sizeof ( undi_isr ) ) ) != 0 )
+		if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_ISR,
+					     &undi_isr,
+					     sizeof ( undi_isr ) ) ) != 0 )
 			break;
 		switch ( undi_isr.FuncFlag ) {
 		case PXENV_UNDI_ISR_OUT_TRANSMIT:
 	}
 
 	/* Close NIC */
-	undinet_call ( undinic, PXENV_UNDI_CLOSE, &undi_close,
-		       sizeof ( undi_close ) );
+	pxeparent_call ( undinet_entry, PXENV_UNDI_CLOSE,
+			 &undi_close, sizeof ( undi_close ) );
 
 	/* Disable interrupt and unhook ISR */
 	disable_irq ( undinic->irq );
 	undi_set_drvdata ( undi, netdev );
 	netdev->dev = &undi->dev;
 	memset ( undinic, 0, sizeof ( *undinic ) );
-	undinet_entry_point = undi->entry;
+	undinet_entry = undi->entry;
 	DBGC ( undinic, "UNDINIC %p using UNDI %p\n", undinic, undi );
 
 	/* Hook in UNDI stack */
 		start_undi.DX = undi->isapnp_read_port;
 		start_undi.ES = BIOS_SEG;
 		start_undi.DI = find_pnp_bios();
-		if ( ( rc = undinet_call ( undinic, PXENV_START_UNDI,
-					   &start_undi,
-					   sizeof ( start_undi ) ) ) != 0 )
+		if ( ( rc = pxeparent_call ( undinet_entry, PXENV_START_UNDI,
+					     &start_undi,
+					     sizeof ( start_undi ) ) ) != 0 )
 			goto err_start_undi;
 	}
 	undi->flags |= UNDI_FL_STARTED;
 	/* Bring up UNDI stack */
 	if ( ! ( undi->flags & UNDI_FL_INITIALIZED ) ) {
 		memset ( &undi_startup, 0, sizeof ( undi_startup ) );
-		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_STARTUP,
-					   &undi_startup,
-					   sizeof ( undi_startup ) ) ) != 0 )
+		if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_STARTUP,
+					     &undi_startup,
+					     sizeof ( undi_startup ) ) ) != 0 )
 			goto err_undi_startup;
 		memset ( &undi_initialize, 0, sizeof ( undi_initialize ) );
-		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_INITIALIZE,
-					   &undi_initialize,
-					   sizeof ( undi_initialize ))) != 0 )
+		if ( ( rc = pxeparent_call ( undinet_entry,
+					     PXENV_UNDI_INITIALIZE,
+					     &undi_initialize,
+					     sizeof ( undi_initialize ))) != 0 )
 			goto err_undi_initialize;
 	}
 	undi->flags |= UNDI_FL_INITIALIZED;
 
 	/* Get device information */
 	memset ( &undi_info, 0, sizeof ( undi_info ) );
-	if ( ( rc = undinet_call ( undinic, PXENV_UNDI_GET_INFORMATION,
-				   &undi_info, sizeof ( undi_info ) ) ) != 0 )
+	if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_GET_INFORMATION,
+				     &undi_info, sizeof ( undi_info ) ) ) != 0 )
 		goto err_undi_get_information;
 	memcpy ( netdev->hw_addr, undi_info.PermNodeAddress, ETH_ALEN );
 	undinic->irq = undi_info.IntNumber;
 
 	/* Get interface information */
 	memset ( &undi_iface, 0, sizeof ( undi_iface ) );
-	if ( ( rc = undinet_call ( undinic, PXENV_UNDI_GET_IFACE_INFO,
-				   &undi_iface,
-				   sizeof ( undi_iface ) ) ) != 0 )
+	if ( ( rc = pxeparent_call ( undinet_entry, PXENV_UNDI_GET_IFACE_INFO,
+				     &undi_iface,
+				     sizeof ( undi_iface ) ) ) != 0 )
 		goto err_undi_get_iface_info;
 	DBGC ( undinic, "UNDINIC %p has type %s, speed %d, flags %08x\n",
 	       undinic, undi_iface.IfaceType, undi_iface.LinkSpeed,
  err_undi_initialize:
 	/* Shut down UNDI stack */
 	memset ( &undi_shutdown, 0, sizeof ( undi_shutdown ) );
-	undinet_call ( undinic, PXENV_UNDI_SHUTDOWN, &undi_shutdown,
-		       sizeof ( undi_shutdown ) );
+	pxeparent_call ( undinet_entry, PXENV_UNDI_SHUTDOWN, &undi_shutdown,
+			 sizeof ( undi_shutdown ) );
 	memset ( &undi_cleanup, 0, sizeof ( undi_cleanup ) );
-	undinet_call ( undinic, PXENV_UNDI_CLEANUP, &undi_cleanup,
-		       sizeof ( undi_cleanup ) );
+	pxeparent_call ( undinet_entry, PXENV_UNDI_CLEANUP, &undi_cleanup,
+			 sizeof ( undi_cleanup ) );
 	undi->flags &= ~UNDI_FL_INITIALIZED;
  err_undi_startup:
 	/* Unhook UNDI stack */
 	memset ( &stop_undi, 0, sizeof ( stop_undi ) );
-	undinet_call ( undinic, PXENV_STOP_UNDI, &stop_undi,
-		       sizeof ( stop_undi ) );
+	pxeparent_call ( undinet_entry, PXENV_STOP_UNDI, &stop_undi,
+			 sizeof ( stop_undi ) );
 	undi->flags &= ~UNDI_FL_STARTED;
  err_start_undi:
 	netdev_nullify ( netdev );
 
 		/* Shut down UNDI stack */
 		memset ( &undi_shutdown, 0, sizeof ( undi_shutdown ) );
-		undinet_call ( undinic, PXENV_UNDI_SHUTDOWN, &undi_shutdown,
-			       sizeof ( undi_shutdown ) );
+		pxeparent_call ( undinet_entry, PXENV_UNDI_SHUTDOWN,
+				 &undi_shutdown, sizeof ( undi_shutdown ) );
 		memset ( &undi_cleanup, 0, sizeof ( undi_cleanup ) );
-		undinet_call ( undinic, PXENV_UNDI_CLEANUP, &undi_cleanup,
-			       sizeof ( undi_cleanup ) );
+		pxeparent_call ( undinet_entry, PXENV_UNDI_CLEANUP,
+				 &undi_cleanup, sizeof ( undi_cleanup ) );
 		undi->flags &= ~UNDI_FL_INITIALIZED;
 
 		/* Unhook UNDI stack */
 		memset ( &stop_undi, 0, sizeof ( stop_undi ) );
-		undinet_call ( undinic, PXENV_STOP_UNDI, &stop_undi,
-			       sizeof ( stop_undi ) );
+		pxeparent_call ( undinet_entry, PXENV_STOP_UNDI, &stop_undi,
+				 sizeof ( stop_undi ) );
 		undi->flags &= ~UNDI_FL_STARTED;
 	}
 
 	/* Clear entry point */
-	memset ( &undinet_entry_point, 0, sizeof ( undinet_entry_point ) );
+	memset ( &undinet_entry, 0, sizeof ( undinet_entry ) );
 
 	/* Free network device */
 	netdev_nullify ( netdev );

src/arch/i386/include/bits/errfile.h

 #define ERRFILE_bios_smbios	( ERRFILE_ARCH | ERRFILE_CORE | 0x00030000 )
 #define ERRFILE_biosint		( ERRFILE_ARCH | ERRFILE_CORE | 0x00040000 )
 #define ERRFILE_int13		( ERRFILE_ARCH | ERRFILE_CORE | 0x00050000 )
+#define ERRFILE_pxeparent	( ERRFILE_ARCH | ERRFILE_CORE | 0x00060000 )
 
 #define ERRFILE_bootsector     ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00000000 )
 #define ERRFILE_bzimage	       ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00010000 )

src/arch/i386/include/pxeparent.h

+#ifndef PXEPARENT_H
+#define PXEPARENT_H
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <pxe_types.h>
+
+extern int pxeparent_call ( SEGOFF16_t entry, unsigned int function,
+			    void *params, size_t params_len );
+
+#endif

src/arch/i386/interface/pxeparent/pxeparent.c

+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 <gpxe/dhcp.h>
+#include <pxeparent.h>
+#include <pxe_api.h>
+#include <pxe_types.h>
+#include <pxe.h>
+
+/** @file
+ *
+ * Call interface to parent PXE stack
+ *
+ */
+
+/**
+ * Name PXE API call
+ *
+ * @v function		API call number
+ * @ret name		API call name
+ */
+static inline __attribute__ (( always_inline )) const char *
+pxeparent_function_name ( unsigned int function ) {
+	switch ( function ) {
+	case PXENV_START_UNDI:
+		return "PXENV_START_UNDI";
+	case PXENV_STOP_UNDI:
+		return "PXENV_STOP_UNDI";
+	case PXENV_UNDI_STARTUP:
+		return "PXENV_UNDI_STARTUP";
+	case PXENV_UNDI_CLEANUP:
+		return "PXENV_UNDI_CLEANUP";
+	case PXENV_UNDI_INITIALIZE:
+		return "PXENV_UNDI_INITIALIZE";
+	case PXENV_UNDI_RESET_ADAPTER:
+		return "PXENV_UNDI_RESET_ADAPTER";
+	case PXENV_UNDI_SHUTDOWN:
+		return "PXENV_UNDI_SHUTDOWN";
+	case PXENV_UNDI_OPEN:
+		return "PXENV_UNDI_OPEN";
+	case PXENV_UNDI_CLOSE:
+		return "PXENV_UNDI_CLOSE";
+	case PXENV_UNDI_TRANSMIT:
+		return "PXENV_UNDI_TRANSMIT";
+	case PXENV_UNDI_SET_MCAST_ADDRESS:
+		return "PXENV_UNDI_SET_MCAST_ADDRESS";
+	case PXENV_UNDI_SET_STATION_ADDRESS:
+		return "PXENV_UNDI_SET_STATION_ADDRESS";
+	case PXENV_UNDI_SET_PACKET_FILTER:
+		return "PXENV_UNDI_SET_PACKET_FILTER";
+	case PXENV_UNDI_GET_INFORMATION:
+		return "PXENV_UNDI_GET_INFORMATION";
+	case PXENV_UNDI_GET_STATISTICS:
+		return "PXENV_UNDI_GET_STATISTICS";
+	case PXENV_UNDI_CLEAR_STATISTICS:
+		return "PXENV_UNDI_CLEAR_STATISTICS";
+	case PXENV_UNDI_INITIATE_DIAGS:
+		return "PXENV_UNDI_INITIATE_DIAGS";
+	case PXENV_UNDI_FORCE_INTERRUPT:
+		return "PXENV_UNDI_FORCE_INTERRUPT";
+	case PXENV_UNDI_GET_MCAST_ADDRESS:
+		return "PXENV_UNDI_GET_MCAST_ADDRESS";
+	case PXENV_UNDI_GET_NIC_TYPE:
+		return "PXENV_UNDI_GET_NIC_TYPE";
+	case PXENV_UNDI_GET_IFACE_INFO:
+		return "PXENV_UNDI_GET_IFACE_INFO";
+	/*
+	 * Duplicate case value; this is a bug in the PXE specification.
+	 *
+	 *	case PXENV_UNDI_GET_STATE:
+	 *		return "PXENV_UNDI_GET_STATE";
+	 */
+	case PXENV_UNDI_ISR:
+		return "PXENV_UNDI_ISR";
+	case PXENV_GET_CACHED_INFO:
+		return "PXENV_GET_CACHED_INFO";
+	default:
+		return "UNKNOWN API CALL";
+	}
+}
+
+/**
+ * PXE parent parameter block
+ *
+ * Used as the paramter block for all parent PXE API calls.  Resides in base
+ * memory.
+ */
+static union u_PXENV_ANY __bss16 ( pxeparent_params );
+#define pxeparent_params __use_data16 ( pxeparent_params )
+
+/** PXE parent entry point
+ *
+ * Used as the indirection vector for all parent PXE API calls.  Resides in
+ * base memory.
+ */
+SEGOFF16_t __bss16 ( pxeparent_entry_point );
+#define pxeparent_entry_point __use_data16 ( pxeparent_entry_point )
+
+/**
+ * Issue parent PXE API call
+ *
+ * @v entry		Parent PXE stack entry point
+ * @v function		API call number
+ * @v params		PXE parameter block
+ * @v params_len	Length of PXE parameter block
+ * @ret rc		Return status code
+ */
+int pxeparent_call ( SEGOFF16_t entry, unsigned int function,
+		     void *params, size_t params_len ) {
+	PXENV_EXIT_t exit;
+	int discard_b, discard_D;
+	int rc;
+
+	/* Copy parameter block and entry point */
+	assert ( params_len <= sizeof ( pxeparent_params ) );
+	memcpy ( &pxeparent_params, params, params_len );
+	memcpy ( &pxeparent_entry_point, &entry, sizeof ( entry ) );
+
+	/* Call real-mode entry point.  This calling convention will
+	 * work with both the !PXE and the PXENV+ entry points.
+	 */
+	__asm__ __volatile__ ( REAL_CODE ( "pushw %%es\n\t"
+					   "pushw %%di\n\t"
+					   "pushw %%bx\n\t"
+					   "lcall *pxeparent_entry_point\n\t"
+					   "addw $6, %%sp\n\t" )
+			       : "=a" ( exit ), "=b" ( discard_b ),
+			         "=D" ( discard_D )
+			       : "b" ( function ),
+			         "D" ( __from_data16 ( &pxeparent_params ) )
+			       : "ecx", "edx", "esi", "ebp" );
+
+	/* PXE API calls may rudely change the status of A20 and not
+	 * bother to restore it afterwards.  Intel is known to be
+	 * guilty of this.
+	 *
+	 * Note that we will return to this point even if A20 gets
+	 * screwed up by the parent PXE stack, because Etherboot always
+	 * resides in an even megabyte of RAM.
+	 */
+	gateA20_set();
+
+	/* Determine return status code based on PXENV_EXIT and
+	 * PXENV_STATUS
+	 */
+	if ( exit == PXENV_EXIT_SUCCESS ) {
+		rc = 0;
+	} else {
+		rc = -pxeparent_params.Status;
+		/* Paranoia; don't return success for the combination
+		 * of PXENV_EXIT_FAILURE but PXENV_STATUS_SUCCESS
+		 */
+		if ( rc == 0 )
+			rc = -EIO;
+	}
+
+	/* If anything goes wrong, print as much debug information as
+	 * it's possible to give.
+	 */
+	if ( rc != 0 ) {
+		SEGOFF16_t rm_params = {
+			.segment = rm_ds,
+			.offset = __from_data16 ( &pxeparent_params ),
+		};
+
+		DBG ( "PXEPARENT %s failed: %s\n",
+		       pxeparent_function_name ( function ), strerror ( rc ) );
+		DBG ( "PXEPARENT parameters at %04x:%04x length "
+		       "%#02zx, entry point at %04x:%04x\n",
+		       rm_params.segment, rm_params.offset, params_len,
+		       pxeparent_entry_point.segment,
+		       pxeparent_entry_point.offset );
+		DBG ( "PXEPARENT parameters provided:\n" );
+		DBG_HDA ( rm_params, params, params_len );
+		DBG ( "PXEPARENT parameters returned:\n" );
+		DBG_HDA ( rm_params, &pxeparent_params, params_len );
+	}
+
+	/* Copy parameter block back */
+	memcpy ( params, &pxeparent_params, params_len );
+
+	return rc;
+}
+