[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/include/ipxe/init.h

@@ -29,6 +29,7 @@ struct init_fn {
 #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

@@ -0,0 +1,16 @@
+#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 */