wipefs: add --backup

[kzak@redhat.com: - don't wipe if failed to create a backup file
                  - use ts_scsi_debug_init in the regression tests]

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

misc-utils/wipefs.8

@@ -40,6 +40,10 @@ erased.
 Erase all available signatures.  The set of erased signatures can be
 restricted with the \fB\-t\fP \fIlist\fP option.
 .TP
+.BR \-b , " \-\-backup"
+Create a signature backup to the file $HOME/wipefs-<devname>-<offset>.bak.
+For more details see EXAMPLES section.
+.TP
 .BR \-f , " \-\-force"
 Force erasure, even if the filesystem is mounted.  This is required in
 order to erase the partition table on a block device.
@@ -75,6 +79,14 @@ taken.  For more details see mount(8).
 .TP
 .BR -V , " \-\-version"
 Output version information and exit.
+.SH EXAMPLES
+.TP
+.BR "wipefs --all --backup /dev/sdb"
+Erases all signatures from the device /dev/sdb and creates a signature backup
+file ~/wipefs-sdb-<offset>.bak for each signature.
+.TP
+.BR "dd if=~/wipefs-sdb-0x00000438.bak of=/dev/sdb seek=$((0x00000438)) bs=1 conv=notrunc"
+Restores ext2 signature from the backup file  ~/wipefs-sdb-0x00000438.bak.
 .SH AUTHOR
 Karel Zak <kzak@redhat.com>
 .SH ENVIRONMENT

misc-utils/wipefs.c

@@ -309,13 +309,33 @@ static void do_wipe_real(blkid_probe pr, const char *devname, struct wipe_desc *
 	putchar('\n');
 }
 
+static void do_backup(struct wipe_desc *wp, const char *base)
+{
+	char *fname = NULL;
+	int fd;
+
+	xasprintf(&fname, "%s0x%08jx.bak", base, wp->offset);
+
+	fd = open(fname, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
+	if (fd < 0)
+		goto err;
+	if (write_all(fd, wp->magic, wp->len) != 0)
+		goto err;
+	close(fd);
+	free(fname);
+	return;
+err:
+	err(EXIT_FAILURE, _("%s: failed to create a signature backup"), fname);
+}
+
 static struct wipe_desc *
-do_wipe(struct wipe_desc *wp, const char *devname, int noact, int all, int quiet, int force)
+do_wipe(struct wipe_desc *wp, const char *devname, int noact, int all, int bkp, int quiet, int force)
 {
 	int flags;
 	blkid_probe pr;
 	struct wipe_desc *w, *wp0;
 	int zap = all ? 1 : wp->zap;
+	char *fn_base = NULL;
 
 	flags = O_RDWR;
 	if (!force)
@@ -324,6 +344,13 @@ do_wipe(struct wipe_desc *wp, const char *devname, int noact, int all, int quiet
 	if (!pr)
 		return NULL;
 
+	if (zap && bkp) {
+		const char *home = getenv ("HOME");
+		if (!home)
+			errx(EXIT_FAILURE, _("failed to create a signature backup, $HOME undefined"));
+		xasprintf (&fn_base, "%s/wipefs-%s-", home, basename(devname));
+	}
+
 	wp0 = clone_offset(wp);
 
 	while (blkid_do_probe(pr) == 0) {
@@ -345,8 +372,11 @@ do_wipe(struct wipe_desc *wp, const char *devname, int noact, int all, int quiet
 		if (!wp->on_disk)
 			continue;
 
-		if (zap)
+		if (zap) {
+			if (bkp)
+				do_backup(wp, fn_base);
 			do_wipe_real(pr, devname, wp, noact, quiet);
+		}
 	}
 
 	for (w = wp0; w != NULL; w = w->next) {
@@ -358,6 +388,7 @@ do_wipe(struct wipe_desc *wp, const char *devname, int noact, int all, int quiet
 	close(blkid_probe_get_fd(pr));
 	blkid_free_probe(pr);
 	free_wipe(wp0);
+	free(fn_base);
 
 	return wp;
 }
@@ -372,6 +403,7 @@ usage(FILE *out)
 
 	fputs(_("\nOptions:\n"), out);
 	fputs(_(" -a, --all           wipe all magic strings (BE CAREFUL!)\n"
+		" -b, --backup        create a signature backup in $HOME\n"
 		" -f, --force         force erasure\n"
 		" -h, --help          show this help text\n"
 		" -n, --no-act        do everything except the actual write() call\n"
@@ -391,11 +423,12 @@ int
 main(int argc, char **argv)
 {
 	struct wipe_desc *wp0 = NULL, *wp;
-	int c, all = 0, force = 0, has_offset = 0, noact = 0, quiet = 0;
+	int c, all = 0, bkp = 0,  force = 0, has_offset = 0, noact = 0, quiet = 0;
 	int mode = WP_MODE_PRETTY;
 
 	static const struct option longopts[] = {
 	    { "all",       0, 0, 'a' },
+	    { "backup",    0, 0, 'b' },
 	    { "force",     0, 0, 'f' },
 	    { "help",      0, 0, 'h' },
 	    { "no-act",    0, 0, 'n' },
@@ -426,6 +459,9 @@ main(int argc, char **argv)
 		case 'a':
 			all++;
 			break;
+		case 'b':
+			bkp++;
+			break;
 		case 'f':
 			force++;
 			break;
@@ -461,6 +497,9 @@ main(int argc, char **argv)
 	if (optind == argc)
 		usage(stderr);
 
+	if (bkp && !(all || has_offset))
+		warnx(_("The --backup option is meaningless in this context"));
+
 	if (!all && !has_offset) {
 		/*
 		 * Print only
@@ -477,7 +516,7 @@ main(int argc, char **argv)
 		 */
 		while (optind < argc) {
 			wp = clone_offset(wp0);
-			wp = do_wipe(wp, argv[optind++], noact, all, quiet,
+			wp = do_wipe(wp, argv[optind++], noact, all, bkp, quiet,
 				     force);
 			free_wipe(wp);
 		}

tests/commands.sh

@@ -66,3 +66,4 @@ TS_CMD_UL=${TS_CMD_UL-"$top_builddir/ul"}
 TS_CMD_UMOUNT=${TS_CMD_UMOUNT:-"$top_builddir/umount"}
 TS_CMD_UTMPDUMP=${TS_CMD_UTMPDUMP-"$top_builddir/utmpdump"}
 TS_CMD_WHEREIS=${TS_CMD_WHEREIS-"$top_builddir/whereis"}
+TS_CMD_WIPEFS=${TS_CMD_WIPEFS-"$top_builddir/wipefs"}

tests/expected/wipefs/wipefs

@@ -0,0 +1 @@
+OK

tests/ts/wipefs/wipefs

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+TS_TOPDIR="$(dirname $0)/../.."
+TS_DESC="wipefs"
+
+. $TS_TOPDIR/functions.sh
+ts_skip_nonroot
+ts_init "$*"
+
+DEVICE=$(ts_scsi_debug_init dev_size_mb=50 num_parts=2)
+
+# remove old backups
+rm -rf $HOME/wipefs-$(basename ${DEVICE})-*.bak
+
+#remove the magic byte, back it up
+$TS_CMD_WIPEFS --all --backup ${DEVICE} &>/dev/null || ts_die "wipefs failed"
+
+#there should be just one magic string/backup file in this case
+INFILE=$(ls $HOME/wipefs-$(basename ${DEVICE})-*.bak)
+OFFT=$(echo $INFILE | sed -E 's/^.*-(.*).bak$/\1/')
+dd if=$INFILE of=$DEVICE bs=1 conv=notrunc seek=$(($OFFT)) &>/dev/null
+
+#the bytes should be copied back, check if wipefs can recognize it
+$TS_CMD_WIPEFS -a ${DEVICE} > $TS_OUTDIR/out 2>/dev/null
+
+# check for output
+[ -s $TS_OUTDIR/out ] && echo "OK" &> $TS_OUTPUT || exit 1
+
+rmmod scsi_debug &>/dev/null
+ts_finalize