[image] Add "imgextract" command for extracting archive images

Add the concept of extracting an image from an archive (which could be
a single-file archive such as a gzip-compressed file), along with an
"imgextract" command to expose this functionality to scripts.

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

src/usr/imgarchive.c

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2021 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., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdio.h>
+#include <ipxe/image.h>
+#include <usr/imgarchive.h>
+
+/** @file
+ *
+ * Archive image management
+ *
+ */
+
+/**
+ * Extract archive image
+ *
+ * @v image		Image
+ * @v name		Extracted image name (or NULL to use default)
+ * @ret rc		Return status code
+ */
+int imgextract ( struct image *image, const char *name ) {
+	struct image *extracted;
+	int rc;
+
+	/* Extract archive image */
+	if ( ( rc = image_extract ( image, name, &extracted ) ) != 0 ) {
+		printf ( "Could not extract image: %s\n", strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}