[prefix] Allow iPXE's own command line to be executed as a script

Some prefixes (e.g. .lkrn) allow a command line to be passed in to
iPXE.  At present, this command line is ignored.

If a command line is provided, treat it as an embedded script (without
an explicit "#!ipxe" magic marker).  This allows for patterns of
invocation such as

  title  iPXE
  kernel /boot/ipxe.lkrn dhcp && \
         sanboot iscsi:10.0.4.1::::iqn.2010-04.org.ipxe.dolphin:storage

Here GRUB is instructed to load ipxe.lkrn with an embedded script
equivalent to

  #!ipxe
  dhcp
  sanboot iscsi:10.0.4.1::::iqn.2010-04.org.ipxe.dolphin:storage

This can be used to effectively vary the embedded script without
having to rebuild ipxe.lkrn.

Originally-implemented-by: Dave Hansen <dave@sr71.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/cmdline.c

+/*
+ * Copyright (C) 2011 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 );
+
+/** @file
+ *
+ * Command line passed to iPXE
+ *
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <ipxe/init.h>
+#include <ipxe/image.h>
+#include <ipxe/script.h>
+#include <realmode.h>
+
+/** Command line physical address
+ *
+ * This can be set by the prefix.
+ */
+uint32_t __bss16 ( cmdline_phys );
+#define cmdline_phys __use_data16 ( cmdline_phys )
+
+/** Internal copy of the command line */
+static char *cmdline_copy;
+
+/** Free command line image */
+static void cmdline_image_free ( struct refcnt *refcnt ) {
+	struct image *image = container_of ( refcnt, struct image, refcnt );
+
+	DBGC ( image, "CMDLINE freeing command line\n" );
+	free ( cmdline_copy );
+}
+
+/** Embedded script representing the command line */
+static struct image cmdline_image = {
+	.refcnt = REF_INIT ( cmdline_image_free ),
+	.name = "<CMDLINE>",
+	.type = &script_image_type,
+};
+
+/**
+ * Initialise command line
+ *
+ */
+static void cmdline_init ( void ) {
+	struct image *image = &cmdline_image;
+	userptr_t cmdline_user;
+	char *cmdline;
+	char *tmp;
+	size_t len;
+
+	/* Do nothing if no command line was specified */
+	if ( ! cmdline_phys ) {
+		DBGC ( image, "CMDLINE found no command line\n" );
+		return;
+	}
+	cmdline_user = phys_to_user ( cmdline_phys );
+	len = ( strlen_user ( cmdline_user, 0 ) + 1 /* NUL */ );
+
+	/* Allocate and copy command line */
+	cmdline_copy = malloc ( len );
+	if ( ! cmdline_copy ) {
+		DBGC ( image, "CMDLINE could not allocate %zd bytes\n", len );
+		/* No way to indicate failure */
+		return;
+	}
+	cmdline = cmdline_copy;
+	copy_from_user ( cmdline, cmdline_user, 0, len );
+	DBGC ( image, "CMDLINE found \"%s\"\n", cmdline );
+
+	/* Check for unwanted cruft in the command line */
+	while ( isspace ( *cmdline ) )
+		cmdline++;
+	if ( ( tmp = strstr ( cmdline, "BOOT_IMAGE=" ) ) != NULL ) {
+		DBGC ( image, "CMDLINE stripping \"%s\"\n", tmp );
+		*tmp = '\0';
+	}
+	DBGC ( image, "CMDLINE using \"%s\"\n", cmdline );
+
+	/* Prepare and register image */
+	cmdline_image.data = virt_to_user ( cmdline );
+	cmdline_image.len = strlen ( cmdline );
+	if ( cmdline_image.len )
+		register_image ( &cmdline_image );
+
+	/* Drop our reference to the image */
+	image_put ( &cmdline_image );
+}
+
+/** Command line initialisation function */
+struct init_fn cmdline_init_fn __init_fn ( INIT_NORMAL ) = {
+	.initialise = cmdline_init,
+};

src/arch/i386/prefix/lkrnprefix.S

 	movw	%ax, %ss
 	movw	$0x7c00, %sp
 
+	/* Retrieve command-line pointer */
+	movl	%es:cmd_line_ptr, %edx
+
 	/* Install iPXE */
 	call	install
 
 	lret
 	.section ".text16", "awx", @progbits
 1:
+	/* Set up %ds for access to .data16 */
+	movw	%bx, %ds
+
+	/* Store command-line pointer */
+	movl	%edx, cmdline_phys
+
+	/* Run iPXE */
 	pushl	$main
 	pushw	%cs
 	call	prot_call

src/image/embedded.c

 }
 
 /** Embedded image initialisation function */
-struct init_fn embedded_init_fn __init_fn ( INIT_NORMAL ) = {
+struct init_fn embedded_init_fn __init_fn ( INIT_LATE ) = {
 	.initialise = embedded_init,
 };

src/image/script.c

 #include <ipxe/image.h>
 #include <ipxe/shell.h>
 #include <usr/prompt.h>
+#include <ipxe/script.h>
 
 /** Currently running script
  *

src/include/ipxe/init.h

 #define INIT_SERIAL	02	/**< Serial driver initialisation */
 #define	INIT_CONSOLE	03	/**< Console initialisation */
 #define INIT_NORMAL	04	/**< Normal initialisation */
+#define INIT_LATE	05	/**< Late initialisation */
 
 /** @} */
 

src/include/ipxe/script.h

+#ifndef _IPXE_SCRIPT_H
+#define _IPXE_SCRIPT_H
+
+/** @file
+ *
+ * iPXE scripts
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <ipxe/image.h>
+
+extern struct image_type script_image_type __image_type ( PROBE_NORMAL );
+
+#endif /* _IPXE_SCRIPT_H */