image-rauc: allow to specify an offset to skip input bytes

This is useful for barebox images on (at least) i.MX8 to be written to
eMMC. There the first 32K of the image must be skipped.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

genimage.h

@@ -45,6 +45,7 @@ struct partition {
 	cfg_bool_t no_automount;
 	cfg_bool_t fill;
 	const char *image;
+	off_t imageoffset;
 	struct list_head list;
 	int autoresize;
 	int in_partition_table;

image-rauc.c

@@ -19,6 +19,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <unistd.h>
 
 #include "genimage.h"
 
@@ -68,6 +69,7 @@ static int rauc_generate(struct image *image)
 		struct image *child = image_get(part->image);
 		const char *file = imageoutfile(child);
 		const char *target = part->name;
+		char *tmptarget;
 		char *path, *tmp;
 
 		if (part->partition_type == RAUC_CERT)
@@ -105,10 +107,34 @@ static int rauc_generate(struct image *image)
 				goto out;
 		}
 
-		image_info(image, "adding file '%s' as '%s' ...\n",
-				child->file, target);
-		ret = systemp(image, "cp --remove-destination '%s' '%s/%s'",
-				file, tmpdir, target);
+		xasprintf(&tmptarget, "%s/%s", tmpdir, target);
+
+		image_info(image, "adding file '%s' as '%s' (offset=%lld)...\n",
+				child->file, target, (long long)part->imageoffset);
+
+		if (part->imageoffset) {
+			unlink(tmptarget);
+
+			/*
+			 * Starting with coreutils 9.1 you can use a 'B' suffix for
+			 * skip=N instead of iflag=skip_bytes to have N count bytes, not
+			 * (input) blocks.
+			 *
+			 * Note that dd doesn't behave as optimal as cp in the
+			 * else branch below because it doesn't preserve holes.
+			 * To improve here insert_image() should be extended to
+			 * support part->imageoffset != 0 and then it can
+			 * replace both commands.
+			 */
+			ret = systemp(image, "dd if='%s' of='%s' iflag=skip_bytes skip=%lld",
+					file, tmptarget, (long long)part->imageoffset);
+
+		} else {
+			ret = systemp(image, "cp --remove-destination '%s' '%s'",
+				      file, tmptarget);
+		}
+
+		free(tmptarget);
 		if (ret)
 			goto out;
 	}
@@ -193,6 +219,7 @@ static int rauc_parse(struct image *image, cfg_t *cfg)
 		part = xzalloc(sizeof *part);
 		part->name = cfg_title(filesec);
 		part->image = cfg_getstr(filesec, "image");
+		part->imageoffset = cfg_getint_suffix(filesec, "offset");
 		part->partition_type = RAUC_CONTENT;
 		list_add_tail(&part->list, &image->partitions);
 	}
@@ -219,6 +246,7 @@ static int rauc_setup(struct image *image, cfg_t *cfg)
 
 static cfg_opt_t file_opts[] = {
 	CFG_STR("image", NULL, CFGF_NONE),
+	CFG_STR("offset", "0", CFGF_NONE),
 	CFG_END()
 };
 

test/misc.test

@@ -31,7 +31,7 @@ setup_rauc() {
 	mkdir input &&
 	cp -r "${testdir}"/rauc-openssl-ca input/ &&
 	echo "test" > input/rauc.content &&
-	echo "test2" > input/rauc2.content
+	echo "xtest2" > input/rauc2.content
 }
 
 exec_test_set_prereq rauc

test/rauc.config

@@ -18,7 +18,10 @@ image test.raucb {
 }
 image test2.raucb {
 	rauc {
-		file data { image = "rauc2.content" }
+		file data {
+			image = "rauc2.content"
+			offset = 1
+		}
 		manifest = "
 			[update]
 			compatible=genimage-test