[cpio] Split out bzImage initrd CPIO header construction

iPXE will construct CPIO headers for images that have a non-empty
command line, thereby allowing raw images (without CPIO headers) to be
injected into a dynamically constructed initrd.  This feature is
currently implemented within the BIOS-only bzImage format support.

Split out the CPIO header construction logic to allow for reuse in
other contexts such as in a UEFI build.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/cpio.h

@@ -9,6 +9,8 @@
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
+#include <ipxe/image.h>
+
 /** A CPIO archive header
  *
  * All field are hexadecimal ASCII numbers padded with '0' on the
@@ -48,6 +50,25 @@ struct cpio_header {
 /** CPIO magic */
 #define CPIO_MAGIC "070701"
 
+/** CPIO header length alignment */
+#define CPIO_ALIGN 4
+
+/** Alignment for CPIO archives within an initrd */
+#define INITRD_ALIGN 4096
+
+/**
+ * Get CPIO image name
+ *
+ * @v image		Image
+ * @ret name		Image name (not NUL terminated)
+ */
+static inline __attribute__ (( always_inline )) const char *
+cpio_name ( struct image *image ) {
+	return image->cmdline;
+}
+
 extern void cpio_set_field ( char *field, unsigned long value );
+extern size_t cpio_name_len ( struct image *image );
+extern size_t cpio_header ( struct image *image, struct cpio_header *cpio );
 
 #endif /* _IPXE_CPIO_H */