[int13] Allow drive to be hooked using the natural drive number

Interpret the maximum drive number (0xff for hard disks, 0x7f for
floppy disks) as meaning "use natural drive number".

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

src/arch/x86/interface/pcbios/int13.c

  *
  * @v uri		URI
  * @v drive		Drive number
- * @ret rc		Return status code
+ * @ret drive		Drive number, or negative error
  *
  * Registers the drive with the INT 13 emulation subsystem, and hooks
  * the INT 13 interrupt vector (if not already hooked).
 	int13_sync_num_drives();
 	natural_drive = ( ( drive & 0x80 ) ? ( num_drives | 0x80 ) : num_fdds );
 
+	/* Use natural drive number if directed to do so */
+	if ( ( drive & 0x7f ) == 0x7f )
+		drive = natural_drive;
+
 	/* Check that drive number is not in use */
 	list_for_each_entry ( int13, &int13s, list ) {
 		if ( int13->drive == drive ) {
 	int13_sync_num_drives();
 
 	free ( scratch );
-	return 0;
+	return drive;
 
  err_guess_geometry:
  err_parse_iso9660:

src/include/ipxe/sanboot.h

  *
  * @v uri		URI
  * @v drive		Drive number
- * @ret rc		Return status code
+ * @ret drive		Drive number, or negative error
  */
 int san_hook ( struct uri *uri, unsigned int drive );
 

src/usr/autoboot.c

 
 	/* Hook SAN device, if applicable */
 	if ( root_path ) {
-		if ( ( rc = san_hook ( root_path, drive ) ) != 0 ) {
+		drive = san_hook ( root_path, drive );
+		if ( drive < 0 ) {
+			rc = drive;
 			printf ( "Could not open SAN device: %s\n",
 				 strerror ( rc ) );
 			goto err_san_hook;
 	}
 
 	/* Describe SAN device, if applicable */
-	if ( ( drive >= 0 ) && ! ( flags & URIBOOT_NO_SAN_DESCRIBE ) ) {
+	if ( ! ( flags & URIBOOT_NO_SAN_DESCRIBE ) ) {
 		if ( ( rc = san_describe ( drive ) ) != 0 ) {
 			printf ( "Could not describe SAN device %#02x: %s\n",
 				 drive, strerror ( rc ) );
 	}
 
 	/* Attempt SAN boot if applicable */
-	if ( ( drive >= 0 ) && ! ( flags & URIBOOT_NO_SAN_BOOT ) ) {
+	if ( ! ( flags & URIBOOT_NO_SAN_BOOT ) ) {
 		if ( fetch_intz_setting ( NULL, &skip_san_boot_setting) == 0 ) {
 			printf ( "Booting from SAN device %#02x\n", drive );
 			rc = san_boot ( drive );
  err_download:
  err_san_describe:
 	/* Unhook SAN device, if applicable */
-	if ( ( drive >= 0 ) && ! ( flags & URIBOOT_NO_SAN_UNHOOK ) ) {
+	if ( ! ( flags & URIBOOT_NO_SAN_UNHOOK ) ) {
 		if ( fetch_intz_setting ( NULL, &keep_san_setting ) == 0 ) {
 			san_unhook ( drive );
 			printf ( "Unregistered SAN device %#02x\n", drive );