Add code for constructing single-file cpio archives on the fly

src/include/gpxe/cpio.h

@@ -0,0 +1,51 @@
+#ifndef _GPXE_CPIO_H
+#define _GPXE_CPIO_H
+
+/** @file
+ *
+ * CPIO archives
+ *
+ */
+
+/** A CPIO archive header
+ *
+ * All field are hexadecimal ASCII numbers padded with '0' on the
+ * left to the full width of the field.
+ */
+struct cpio_header {
+	/** The string "070701" or "070702" */
+	char c_magic[6];
+	/** File inode number */
+	char c_ino[8];
+	/** File mode and permissions */
+	char c_mode[8];
+	/** File uid */
+	char c_uid[8];
+	/** File gid */
+	char c_gid[8];
+	/** Number of links */
+	char c_nlink[8];
+	/** Modification time */
+	char c_mtime[8];
+	/** Size of data field */
+	char c_filesize[8];
+	/** Major part of file device number */
+	char c_maj[8];
+	/** Minor part of file device number */
+	char c_min[8];
+	/** Major part of device node reference */
+	char c_rmaj[8];
+	/** Minor part of device node reference */
+	char c_rmin[8];
+	/** Length of filename, including final NUL */
+	char c_namesize[8];
+	/** Checksum of data field if c_magic is 070702, othersize zero */
+	char c_chksum[8];
+} __attribute__ (( packed ));
+
+/** CPIO magic */
+#define CPIO_MAGIC "070701"
+
+extern void cpio_set_field ( char *field, unsigned long value );
+
+#endif /* _GPXE_CPIO_H */