Refactor zhack label repair and fix -c regression on nonzero TXG

This commit fixes a likely regression introduced by 64db435 where the
checksum repair functionality (`-c` or default behavior) will perform
checks and access data associated with the newer undetach (`-u`)
functionality, resulting in a failure when an uberblock's TXG is not 0
as required by `-u` but not `-c`

Additionally, code is refactored for better separation of tasks.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: buzzingwires <buzzingwires@outlook.com>
Closes #17732

cmd/zhack.c

@@ -714,6 +714,23 @@ zhack_repair_read_label(const int fd, vdev_label_t *vl,
 	return (0);
 }
 
+static int
+zhack_repair_get_byteswap(const zio_eck_t *vdev_eck, const int l, int *byteswap)
+{
+	if (vdev_eck->zec_magic == ZEC_MAGIC) {
+		*byteswap = B_FALSE;
+	} else if (vdev_eck->zec_magic == BSWAP_64((uint64_t)ZEC_MAGIC)) {
+		*byteswap = B_TRUE;
+	} else {
+		(void) fprintf(stderr, "error: label %d: "
+		    "Expected the nvlist checksum magic number but instead got "
+		    "0x%" PRIx64 "\n",
+		    l, vdev_eck->zec_magic);
+		return (1);
+	}
+	return (0);
+}
+
 static void
 zhack_repair_calc_cksum(const int byteswap, void *data, const uint64_t offset,
     const uint64_t abdsize, zio_eck_t *eck, zio_cksum_t *cksum)
@@ -740,33 +757,10 @@ zhack_repair_calc_cksum(const int byteswap, void *data, const uint64_t offset,
 }
 
 static int
-zhack_repair_check_label(uberblock_t *ub, const int l, const char **cfg_keys,
+zhack_repair_get_ashift(nvlist_t *cfg, const int l, uint64_t *ashift)
-    const size_t cfg_keys_len, nvlist_t *cfg, nvlist_t *vdev_tree_cfg,
-    uint64_t *ashift)
 {
 	int err;
-
+	nvlist_t *vdev_tree_cfg;
-	if (ub->ub_txg != 0) {
-		(void) fprintf(stderr,
-		    "error: label %d: UB TXG of 0 expected, but got %"
-		    PRIu64 "\n",
-		    l, ub->ub_txg);
-		(void) fprintf(stderr, "It would appear the device was not "
-		    "properly removed.\n");
-		return (1);
-	}
-
-	for (int i = 0; i < cfg_keys_len; i++) {
-		uint64_t val;
-		err = nvlist_lookup_uint64(cfg, cfg_keys[i], &val);
-		if (err) {
-			(void) fprintf(stderr,
-			    "error: label %d, %d: "
-			    "cannot find nvlist key %s\n",
-			    l, i, cfg_keys[i]);
-			return (err);
-		}
-	}
 
 	err = nvlist_lookup_nvlist(cfg,
 	    ZPOOL_CONFIG_VDEV_TREE, &vdev_tree_cfg);
@@ -790,7 +784,7 @@ zhack_repair_check_label(uberblock_t *ub, const int l, const char **cfg_keys,
 		(void) fprintf(stderr,
 		    "error: label %d: nvlist key %s is zero\n",
 		    l, ZPOOL_CONFIG_ASHIFT);
-		return (err);
+		return (1);
 	}
 
 	return (0);
@@ -805,30 +799,35 @@ zhack_repair_undetach(uberblock_t *ub, nvlist_t *cfg, const int l)
 	 */
 	if (BP_GET_LOGICAL_BIRTH(&ub->ub_rootbp) != 0) {
 		const uint64_t txg = BP_GET_LOGICAL_BIRTH(&ub->ub_rootbp);
+		int err;
+
 		ub->ub_txg = txg;
 
-		if (nvlist_remove_all(cfg, ZPOOL_CONFIG_CREATE_TXG) != 0) {
+		err = nvlist_remove_all(cfg, ZPOOL_CONFIG_CREATE_TXG);
+		if (err) {
 			(void) fprintf(stderr,
 			    "error: label %d: "
 			    "Failed to remove pool creation TXG\n",
 			    l);
-			return (1);
+			return (err);
 		}
 
-		if (nvlist_remove_all(cfg, ZPOOL_CONFIG_POOL_TXG) != 0) {
+		err = nvlist_remove_all(cfg, ZPOOL_CONFIG_POOL_TXG);
+		if (err) {
 			(void) fprintf(stderr,
 			    "error: label %d: Failed to remove pool TXG to "
 			    "be replaced.\n",
 			    l);
-			return (1);
+			return (err);
 		}
 
-		if (nvlist_add_uint64(cfg, ZPOOL_CONFIG_POOL_TXG, txg) != 0) {
+		err = nvlist_add_uint64(cfg, ZPOOL_CONFIG_POOL_TXG, txg);
+		if (err) {
 			(void) fprintf(stderr,
 			    "error: label %d: "
 			    "Failed to add pool TXG of %" PRIu64 "\n",
 			    l, txg);
-			return (1);
+			return (err);
 		}
 	}
 
@@ -922,6 +921,7 @@ zhack_repair_test_cksum(const int byteswap, void *vdev_data,
 	    BSWAP_64(ZEC_MAGIC) : ZEC_MAGIC;
 	const uint64_t actual_magic = vdev_eck->zec_magic;
 	int err = 0;
+
 	if (actual_magic != expected_magic) {
 		(void) fprintf(stderr, "error: label %d: "
 		    "Expected "
@@ -943,6 +943,36 @@ zhack_repair_test_cksum(const int byteswap, void *vdev_data,
 	return (err);
 }
 
+static int
+zhack_repair_unpack_cfg(vdev_label_t *vl, const int l, nvlist_t **cfg)
+{
+	const char *cfg_keys[] = { ZPOOL_CONFIG_VERSION,
+	    ZPOOL_CONFIG_POOL_STATE, ZPOOL_CONFIG_GUID };
+	int err;
+
+	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);
+		return (err);
+	}
+
+	for (int i = 0; i < ARRAY_SIZE(cfg_keys); i++) {
+		uint64_t val;
+		err = nvlist_lookup_uint64(*cfg, cfg_keys[i], &val);
+		if (err) {
+			(void) fprintf(stderr,
+			    "error: label %d, %d: "
+			    "cannot find nvlist key %s\n",
+			    l, i, cfg_keys[i]);
+			return (err);
+		}
+	}
+
+	return (0);
+}
+
 static void
 zhack_repair_one_label(const zhack_repair_op_t op, const int fd,
     vdev_label_t *vl, const uint64_t label_offset, const int l,
@@ -956,10 +986,7 @@ zhack_repair_one_label(const zhack_repair_op_t op, const int fd,
 	    (zio_eck_t *)((char *)(vdev_data) + VDEV_PHYS_SIZE) - 1;
 	const uint64_t vdev_phys_offset =
 	    label_offset + offsetof(vdev_label_t, vl_vdev_phys);
-	const char *cfg_keys[] = { ZPOOL_CONFIG_VERSION,
-	    ZPOOL_CONFIG_POOL_STATE, ZPOOL_CONFIG_GUID };
 	nvlist_t *cfg;
-	nvlist_t *vdev_tree_cfg = NULL;
 	uint64_t ashift;
 	int byteswap;
 
@@ -967,18 +994,9 @@ zhack_repair_one_label(const zhack_repair_op_t op, const int fd,
 	if (err)
 		return;
 
-	if (vdev_eck->zec_magic == 0) {
+	err = zhack_repair_get_byteswap(vdev_eck, l, &byteswap);
-		(void) fprintf(stderr, "error: label %d: "
+	if (err)
-		    "Expected the nvlist checksum magic number to not be zero"
-		    "\n",
-		    l);
-		(void) fprintf(stderr, "There should already be a checksum "
-		    "for the label.\n");
 		return;
-	}
-
-	byteswap =
-	    (vdev_eck->zec_magic == BSWAP_64((uint64_t)ZEC_MAGIC));
 
 	if (byteswap) {
 		byteswap_uint64_array(&vdev_eck->zec_cksum,
@@ -994,16 +1012,7 @@ zhack_repair_one_label(const zhack_repair_op_t op, const int fd,
 		return;
 	}
 
-	err = nvlist_unpack(vl->vl_vdev_phys.vp_nvlist,
+	err = zhack_repair_unpack_cfg(vl, l, &cfg);
-	    VDEV_PHYS_SIZE - sizeof (zio_eck_t), &cfg, 0);
-	if (err) {
-		(void) fprintf(stderr,
-		    "error: cannot unpack nvlist label %d\n", l);
-		return;
-	}
-
-	err = zhack_repair_check_label(ub,
-	    l, cfg_keys, ARRAY_SIZE(cfg_keys), cfg, vdev_tree_cfg, &ashift);
 	if (err)
 		return;
 
@@ -1011,6 +1020,19 @@ zhack_repair_one_label(const zhack_repair_op_t op, const int fd,
 		char *buf;
 		size_t buflen;
 
+		if (ub->ub_txg != 0) {
+			(void) fprintf(stderr,
+			    "error: label %d: UB TXG of 0 expected, but got %"
+			    PRIu64 "\n", l, ub->ub_txg);
+			(void) fprintf(stderr, "It would appear the device was "
+			    "not properly detached.\n");
+			return;
+		}
+
+		err = zhack_repair_get_ashift(cfg, l, &ashift);
+		if (err)
+			return;
+
 		err = zhack_repair_undetach(ub, cfg, l);
 		if (err)
 			return;

tests/zfs-tests/tests/functional/cli_root/zhack/library.kshlib

@@ -33,13 +33,16 @@
 # Test one:
 #
 # 1. Create pool on a loopback device with some test data
-# 2. Export the pool.
+# 2. Checksum repair should work with a valid TXG. Repeatedly write and
-# 3. Corrupt all label checksums in the pool
+#    sync the pool so there are enough transactions for every uberblock
-# 4. Check that pool cannot be imported
+#    to have a TXG
-# 5. Verify that it cannot be imported after using zhack label repair -u
+# 3. Export the pool.
+# 4. Corrupt all label checksums in the pool
+# 5. Check that pool cannot be imported
+# 6. Verify that it cannot be imported after using zhack label repair -u
 #    to ensure that the -u option will quit on corrupted checksums.
-# 6. Use zhack label repair -c on device
+# 7. Use zhack label repair -c on device
-# 7. Check that pool can be imported and that data is intact
+# 8. Check that pool can be imported and that data is intact
 #
 # Test two:
 #
@@ -170,6 +173,17 @@ function setup_dataset
 	check_dataset true
 }
 
+function force_transactions
+{
+	L_TIMES="$1"
+	for ((i=0; i < L_TIMES; i++))
+	do
+		touch "$TESTDIR"/"test" || return $?
+		zpool sync -f "$TESTPOOL" || return $?
+	done
+	return 0
+}
+
 function get_practical_size
 {
 	L_SIZE="$1"
@@ -257,6 +271,9 @@ function run_test_one
 
 	setup_dataset
 
+	# Force 256 extra transactions to ensure all uberblocks are assigned a TXG
+	log_must force_transactions 256
+
 	log_must zpool export "$TESTPOOL"
 
 	corrupt_labels "$L_SIZE" "$VIRTUAL_DISK"

tests/zfs-tests/tests/functional/cli_root/zhack/zhack_label_repair_001.ksh

@@ -18,13 +18,16 @@
 # Strategy:
 #
 # 1. Create pool on a loopback device with some test data
-# 2. Export the pool.
+# 2. Checksum repair should work with a valid TXG. Repeatedly write and
-# 3. Corrupt all label checksums in the pool
+#    sync the pool so there are enough transactions for every uberblock
-# 4. Check that pool cannot be imported
+#    to have a TXG
-# 5. Verify that it cannot be imported after using zhack label repair -u
+# 3. Export the pool.
+# 4. Corrupt all label checksums in the pool
+# 5. Check that pool cannot be imported
+# 6. Verify that it cannot be imported after using zhack label repair -u
 #    to ensure that the -u option will quit on corrupted checksums.
-# 6. Use zhack label repair -c on device
+# 7. Use zhack label repair -c on device
-# 7. Check that pool can be imported and that data is intact
+# 8. Check that pool can be imported and that data is intact
 
 . "$STF_SUITE"/tests/functional/cli_root/zhack/library.kshlib