Add --dry-run-metadata boilerplate (no functionality)

The only interesting facets of this commit are:

- internally, we store this as bsdtar->option_dryrun == 2; the existing
  --dry-run option is stored as 1.

- we disallow the combination of --dry-run-metadata with --print-stats,
  because the --print-stats (generated from the chunk layer) would only
  report metadata and metaindex bytes (since no filesystem data will
  reach the chunk layer).

tar/bsdtar.c

@@ -463,8 +463,17 @@ main(int argc, char **argv)
 			optq_push(bsdtar, "disk-pause", bsdtar->optarg);
 			break;
 		case OPTION_DRYRUN: /* tarsnap */
+			if (bsdtar->option_dryrun != 0)
+				bsdtar_errc(bsdtar, 1, 0,
+				    "Can only specify one --dry-run* option");
 			bsdtar->option_dryrun = 1;
 			break;
+		case OPTION_DRYRUN_METADATA: /* tarsnap */
+			if (bsdtar->option_dryrun != 0)
+				bsdtar_errc(bsdtar, 1, 0,
+				    "Can only specify one --dry-run* option");
+			bsdtar->option_dryrun = 2;
+			break;
 		case OPTION_EXCLUDE: /* GNU tar */
 			optq_push(bsdtar, "exclude", bsdtar->optarg);
 			break;
@@ -988,6 +997,9 @@ main(int argc, char **argv)
 			tarsnap_opt_aggressive_networking = 0;
 		}
 	}
+	if ((bsdtar->option_dryrun == 2) && bsdtar->option_print_stats)
+		bsdtar_errc(bsdtar, 1, 0, "--dry-run-metadata is "
+		    "incompatible with --print-stats");
 
 	/*
 	 * The -f option doesn't make sense for --fsck, --fsck-prune, or
@@ -1044,8 +1056,10 @@ main(int argc, char **argv)
 		only_mode(bsdtar, "-U", "x");
 	if (bsdtar->option_warn_links)
 		only_mode(bsdtar, "--check-links", "c");
-	if (bsdtar->option_dryrun)
+	if (bsdtar->option_dryrun == 1)
 		only_mode(bsdtar, "--dry-run", "c");
+	if (bsdtar->option_dryrun == 2)
+		only_mode(bsdtar, "--dry-run-metadata", "c");
 
 	/* Check other parameters only permitted in certain modes. */
 	if (bsdtar->symlink_mode != '\0') {

tar/bsdtar.h

@@ -75,7 +75,7 @@ struct bsdtar {
 	char		  option_chroot; /* --chroot */
 	char		 *option_csv_filename; /* --csv-filename */
 	char		  option_dont_traverse_mounts; /* --one-file-system */
-	char		  option_dryrun; /* --dry-run */
+	char		  option_dryrun; /* --dry-run / --dry-run-metadata */
 	char		  option_fast_read; /* --fast-read */
 	int               option_hashes;
 	char		  option_honor_nodump; /* --nodump */
@@ -207,6 +207,7 @@ enum {
 	OPTION_DEBUG_NETWORK_STATS,
 	OPTION_DISK_PAUSE,
 	OPTION_DRYRUN,
+	OPTION_DRYRUN_METADATA,
 	OPTION_DUMP_CONFIG,
 	OPTION_EXCLUDE,
 	OPTION_FORCE_RESOURCES,

tar/cmdline.c

@@ -85,6 +85,7 @@ static struct option {
 	{ "directory",            1, 'C' },
 	{ "disk-pause",		  1, OPTION_DISK_PAUSE },
 	{ "dry-run",		  0, OPTION_DRYRUN },
+	{ "dry-run-metadata",	  0, OPTION_DRYRUN_METADATA },
 	{ "dump-config",	  0, OPTION_DUMP_CONFIG },
 	{ "exclude",              1, OPTION_EXCLUDE },
 	{ "exclude-from",         1, 'X' },