zhack: Add repair label option

In case if all label checksums will be invalid on any vdev, the pool
will become unimportable. The zhack with newly added cli options could
be used to restore label checksums and make pool importable again.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Fedor Uporov <fuporov.vstack@gmail.com>
Closes openzfs#2510
Closes openzfs#12686

cmd/zhack/zhack.c

@@ -33,6 +33,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>
+#include <sys/stat.h>
 #include <sys/zfs_context.h>
 #include <sys/spa.h>
 #include <sys/spa_impl.h>
@@ -41,6 +42,7 @@
 #include <sys/zfs_znode.h>
 #include <sys/dsl_synctask.h>
 #include <sys/vdev.h>
+#include <sys/vdev_impl.h>
 #include <sys/fs/zfs.h>
 #include <sys/dmu_objset.h>
 #include <sys/dsl_pool.h>
@@ -76,7 +78,12 @@ usage(void)
 	    "        -d decrease instead of increase the refcount\n"
 	    "        -m add the feature to the label if increasing refcount\n"
 	    "\n"
-	    "    <feature> : should be a feature guid\n");
+	    "    <feature> : should be a feature guid\n"
+	    "\n"
+	    "    label repair <device>\n"
+	    "        repair corrupted label checksums\n"
+	    "\n"
+	    "    <device> : path to vdev\n");
 	exit(1);
 }
 
@@ -471,6 +478,166 @@ zhack_do_feature(int argc, char **argv)
 	return (0);
 }
 
+static int
+zhack_repair_label_cksum(int argc, char **argv)
+{
+	zio_checksum_info_t *ci = &zio_checksum_table[ZIO_CHECKSUM_LABEL];
+	const char *cfg_keys[] = { ZPOOL_CONFIG_VERSION,
+	    ZPOOL_CONFIG_POOL_STATE, ZPOOL_CONFIG_GUID };
+	boolean_t labels_repaired[VDEV_LABELS];
+	boolean_t repaired = B_FALSE;
+	vdev_label_t labels[VDEV_LABELS];
+	struct stat st;
+	int fd;
+
+	bzero(labels_repaired, sizeof (labels_repaired));
+	bzero(labels, sizeof (labels));
+
+	abd_init();
+
+	argc -= 1;
+	argv += 1;
+
+	if (argc < 1) {
+		(void) fprintf(stderr, "error: missing device\n");
+		usage();
+	}
+
+	if ((fd = open(argv[0], O_RDWR)) == -1)
+		fatal(NULL, FTAG, "cannot open '%s': %s", argv[0],
+		    strerror(errno));
+
+	if (stat(argv[0], &st) != 0)
+		fatal(NULL, FTAG, "cannot stat '%s': %s", argv[0],
+		    strerror(errno));
+
+	for (int l = 0; l < VDEV_LABELS; l++) {
+		uint64_t label_offset, offset;
+		zio_cksum_t expected_cksum;
+		zio_cksum_t actual_cksum;
+		zio_cksum_t verifier;
+		zio_eck_t *eck;
+		nvlist_t *cfg;
+		int byteswap;
+		uint64_t val;
+		ssize_t err;
+
+		vdev_label_t *vl = &labels[l];
+
+		label_offset = vdev_label_offset(st.st_size, l, 0);
+		err = pread64(fd, vl, sizeof (vdev_label_t), label_offset);
+		if (err == -1) {
+			(void) fprintf(stderr, "error: cannot read "
+			    "label %d: %s\n", l, strerror(errno));
+			continue;
+		} else if (err != sizeof (vdev_label_t)) {
+			(void) fprintf(stderr, "error: bad label %d read size "
+			    "\n", l);
+			continue;
+		}
+
+		err = nvlist_unpack(vl->vl_vdev_phys.vp_nvlist,
+		    VDEV_PHYS_SIZE - sizeof (zio_eck_t), &cfg, 0);
+		if (err) {
+			(void) fprintf(stderr, "error: cannot unpack nvlist "
+			    "label %d\n", l);
+			continue;
+		}
+
+		for (int i = 0; i < ARRAY_SIZE(cfg_keys); i++) {
+			err = nvlist_lookup_uint64(cfg, cfg_keys[i], &val);
+			if (err) {
+				(void) fprintf(stderr, "error: label %d: "
+				    "cannot find nvlist key %s\n",
+				    l, cfg_keys[i]);
+				continue;
+			}
+		}
+
+		void *data = (char *)vl + offsetof(vdev_label_t, vl_vdev_phys);
+		eck = (zio_eck_t *)((char *)(data) + VDEV_PHYS_SIZE) - 1;
+
+		offset = label_offset + offsetof(vdev_label_t, vl_vdev_phys);
+		ZIO_SET_CHECKSUM(&verifier, offset, 0, 0, 0);
+
+		byteswap = (eck->zec_magic == BSWAP_64(ZEC_MAGIC));
+		if (byteswap)
+			byteswap_uint64_array(&verifier, sizeof (zio_cksum_t));
+
+		expected_cksum = eck->zec_cksum;
+		eck->zec_cksum = verifier;
+
+		abd_t *abd = abd_get_from_buf(data, VDEV_PHYS_SIZE);
+		ci->ci_func[byteswap](abd, VDEV_PHYS_SIZE, NULL, &actual_cksum);
+		abd_free(abd);
+
+		if (byteswap)
+			byteswap_uint64_array(&expected_cksum,
+			    sizeof (zio_cksum_t));
+
+		if (ZIO_CHECKSUM_EQUAL(actual_cksum, expected_cksum))
+			continue;
+
+		eck->zec_cksum = actual_cksum;
+
+		err = pwrite64(fd, data, VDEV_PHYS_SIZE, offset);
+		if (err == -1) {
+			(void) fprintf(stderr, "error: cannot write "
+			    "label %d: %s\n", l, strerror(errno));
+			continue;
+		} else if (err != VDEV_PHYS_SIZE) {
+			(void) fprintf(stderr, "error: bad write size "
+			    "label %d\n", l);
+			continue;
+		}
+
+		fsync(fd);
+
+		labels_repaired[l] = B_TRUE;
+	}
+
+	close(fd);
+
+	abd_fini();
+
+	for (int l = 0; l < VDEV_LABELS; l++) {
+		(void) printf("label %d: %s\n", l,
+		    labels_repaired[l] ? "repaired" : "skipped");
+		repaired |= labels_repaired[l];
+	}
+
+	if (repaired)
+		return (0);
+
+	return (1);
+}
+
+static int
+zhack_do_label(int argc, char **argv)
+{
+	char *subcommand;
+	int err;
+
+	argc--;
+	argv++;
+	if (argc == 0) {
+		(void) fprintf(stderr,
+		    "error: no label operation specified\n");
+		usage();
+	}
+
+	subcommand = argv[0];
+	if (strcmp(subcommand, "repair") == 0) {
+		err = zhack_repair_label_cksum(argc, argv);
+	} else {
+		(void) fprintf(stderr, "error: unknown subcommand: %s\n",
+		    subcommand);
+		usage();
+	}
+
+	return (err);
+}
+
 #define	MAX_NUM_PATHS 1024
 
 int
@@ -516,6 +683,8 @@ main(int argc, char **argv)
 
 	if (strcmp(subcommand, "feature") == 0) {
 		rv = zhack_do_feature(argc, argv);
+	} else if (strcmp(subcommand, "label") == 0) {
+		return (zhack_do_label(argc, argv));
 	} else {
 		(void) fprintf(stderr, "error: unknown subcommand: %s\n",
 		    subcommand);

configure.ac

@@ -288,6 +288,7 @@ AC_CONFIG_FILES([
 	tests/zfs-tests/tests/functional/cli_root/zfs_unshare/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_upgrade/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_wait/Makefile
+	tests/zfs-tests/tests/functional/cli_root/zhack/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zpool/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zpool_add/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zpool_attach/Makefile

man/man1/zhack.1

@@ -94,6 +94,13 @@ The
 flag indicates that the
 .Ar guid
 feature is now required to read the pool MOS.
+.
+.It Xo
+.Nm zhack
+.Cm label repair
+.Ar device
+.Xc
+Repair corrupted labels by rewriting the checksum using the presumed valid contents of the label.
 .El
 .
 .Sh GLOBAL OPTIONS

tests/runfiles/common.run

@@ -317,6 +317,12 @@ tags = ['functional', 'cli_root', 'zfs_upgrade']
 tests = ['zfs_wait_deleteq']
 tags = ['functional', 'cli_root', 'zfs_wait']
 
+[tests/functional/cli_root/zhack]
+tests = ['zhack_label_checksum']
+pre =
+post =
+tags = ['functional', 'cli_root', 'zhack']
+
 [tests/functional/cli_root/zpool]
 tests = ['zpool_001_neg', 'zpool_002_pos', 'zpool_003_pos', 'zpool_colors']
 tags = ['functional', 'cli_root', 'zpool']

tests/zfs-tests/tests/functional/cli_root/Makefile.am

@@ -35,6 +35,7 @@ SUBDIRS = \
 	zfs_unshare \
 	zfs_upgrade \
 	zfs_wait \
+	zhack \
 	zpool \
 	zpool_add \
 	zpool_attach \

tests/zfs-tests/tests/functional/cli_root/zhack/Makefile.am

@@ -0,0 +1,3 @@
+pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/cli_root/zhack
+dist_pkgdata_SCRIPTS = \
+	zhack_label_checksum.ksh

tests/zfs-tests/tests/functional/cli_root/zhack/zhack_label_checksum.ksh

@@ -0,0 +1,64 @@
+#!/bin/ksh
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2021 by vStack. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/include/blkdev.shlib
+
+#
+# Description:
+# zhack label repair <vdev> will calculate and rewrite label checksum if invalid
+#
+# Strategy:
+# 1. Create pool with some number of vdevs and export it
+# 2. Corrupt all labels checksums
+# 3. Check that pool cannot be imported
+# 4. Use zhack to repair labels checksums
+# 5. Check that pool can be imported
+#
+
+log_assert "Verify zhack label repair <vdev> will repair labels checksums"
+log_onexit cleanup
+
+VIRTUAL_DISK=$TEST_BASE_DIR/disk
+
+function cleanup
+{
+	poolexists $TESTPOOL && destroy_pool $TESTPOOL
+	[[ -f $VIRTUAL_DISK ]] && log_must rm $VIRTUAL_DISK
+}
+
+log_must truncate -s $(($MINVDEVSIZE * 8)) $VIRTUAL_DISK
+
+log_must zpool create $TESTPOOL $VIRTUAL_DISK
+log_must zpool export $TESTPOOL
+
+log_mustnot zhack label repair $VIRTUAL_DISK
+
+corrupt_label_checksum 0 $VIRTUAL_DISK
+corrupt_label_checksum 1 $VIRTUAL_DISK
+corrupt_label_checksum 2 $VIRTUAL_DISK
+corrupt_label_checksum 3 $VIRTUAL_DISK
+
+log_mustnot zpool import $TESTPOOL -d $TEST_BASE_DIR
+
+log_must zhack label repair $VIRTUAL_DISK
+
+log_must zpool import $TESTPOOL -d $TEST_BASE_DIR
+
+cleanup
+
+log_pass "zhack label repair works correctly."