util/cbfstool: Add "truncate" command

It does the opposite to "expand", removing a trailing empty file from
CBFS. It also returns the size of the CBFS post processing on stdout.

BUG=b:65853903
BRANCH=none
TEST=`cbfstool test.bin truncate -r FW_MAIN_A` removes the trailing
empty file in FW_MAIN_A. Without a trailing empty file, the region is
left alone (tested using COREBOOT which comes with a master header
pointer).

Change-Id: I0c747090813898539f3428936afa9d8459adee9c
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/21608
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

util/cbfstool/cbfs_image.c

@@ -480,6 +480,44 @@ int cbfs_expand_to_region(struct buffer *region)
 	return 0;
 }
 
+int cbfs_truncate_space(struct buffer *region, uint32_t *size)
+{
+	if (buffer_get(region) == NULL)
+		return 1;
+
+	struct cbfs_image image;
+	memset(&image, 0, sizeof(image));
+	if (cbfs_image_from_buffer(&image, region, 0)) {
+		ERROR("reading CBFS failed!\n");
+		return 1;
+	}
+
+	struct cbfs_file *entry, *trailer;
+	for (trailer = entry = buffer_get(region);
+	     cbfs_is_valid_entry(&image, entry);
+	     trailer = entry,
+	     entry = cbfs_find_next_entry(&image, entry)) {
+	     /* just iterate through */
+	}
+
+	/* trailer now points to the last valid CBFS entry's header.
+	 * If that file is empty, remove it and report its header's offset as
+	 * maximum size.
+	 */
+	if ((strlen(trailer->filename) != 0) &&
+	    (trailer->type != htonl(CBFS_COMPONENT_NULL)) &&
+	    (trailer->type != htonl(CBFS_COMPONENT_DELETED))) {
+		/* nothing to truncate. Return de-facto CBFS size in case it
+		 * was already truncated. */
+		*size = (void *)entry - buffer_get(region);
+		return 0;
+	}
+	*size = (void *)trailer - buffer_get(region);
+	memset(trailer, 0xff, buffer_size(region) - *size);
+
+	return 0;
+}
+
 static size_t cbfs_file_entry_metadata_size(const struct cbfs_file *f)
 {
 	return ntohl(f->offset);

util/cbfstool/cbfs_image.h

@@ -84,6 +84,11 @@ int cbfs_compact_instance(struct cbfs_image *image);
    Returns 0 on success, otherwise non-zero. */
 int cbfs_expand_to_region(struct buffer *region);
 
+/* Truncate a CBFS by removing a trailing "empty" file if it exists.
+   Returns 0 on success, otherwise non-zero and passes the CBFS' remaining
+   size in the size argument. */
+int cbfs_truncate_space(struct buffer *region, uint32_t *size);
+
 /* Releases the CBFS image. Returns 0 on success, otherwise non-zero. */
 int cbfs_image_delete(struct cbfs_image *image);
 

util/cbfstool/cbfstool.c

@@ -1121,6 +1121,23 @@ static int cbfs_expand(void)
 	return cbfs_expand_to_region(param.image_region);
 }
 
+static int cbfs_truncate(void)
+{
+	struct buffer src_buf;
+
+	/* Obtain the source region. */
+	if (!partitioned_file_read_region(&src_buf, param.image_file,
+						param.region_name)) {
+		ERROR("Region not found in image: %s\n", param.source_region);
+		return 1;
+	}
+
+	uint32_t size;
+	int result = cbfs_truncate_space(param.image_region, &size);
+	printf("0x%x\n", size);
+	return result;
+}
+
 static const struct command commands[] = {
 	{"add", "H:r:f:n:t:c:b:a:yvA:gh?", cbfs_add, true, true},
 	{"add-flat-binary", "H:r:f:n:l:e:c:b:vA:gh?", cbfs_add_flat_binary,
@@ -1142,6 +1159,7 @@ static const struct command commands[] = {
 	{"update-fit", "H:r:n:x:vh?", cbfs_update_fit, true, true},
 	{"write", "r:f:i:Fudvh?", cbfs_write, true, true},
 	{"expand", "r:h?", cbfs_expand, true, true},
+	{"truncate", "r:h?", cbfs_truncate, true, true},
 };
 
 static struct option long_options[] = {
@@ -1291,6 +1309,8 @@ static void usage(char *name)
 			"Write file into same-size [or larger] raw region\n"
 	     " read [-r fmap-region] -f file                               "
 			"Extract raw region contents into binary file\n"
+	     " truncate [-r fmap-region]                                   "
+			"Truncate CBFS and print new size on stdout\n"
 	     " expand [-r fmap-region]                                     "
 			"Expand CBFS to span entire region\n"
 	     " update-fit [-r image,regions] -n MICROCODE_BLOB_NAME \\\n"