Add 'zpool import --load-meta-thresh [n]' option

When attempting to import a pool, spa_load_verify() fails if there are
any metadata errors.  This commit adds a new 'zpool import
--load-meta-thresh [n]' option, which allows you to specify how many
metadata errors to permit when importing.

Signed-off-by: Steve Mokris <smokris@softpixel.com>

cmd/zpool/zpool_main.c

@@ -2939,6 +2939,7 @@ zpool_do_checkpoint(int argc, char **argv)
 }
 
 #define	CHECKPOINT_OPT	1024
+#define	LOAD_META_THRESH_OPT	1025
 
 /*
  * zpool import [-d dir] [-D]
@@ -3024,9 +3025,11 @@ zpool_do_import(int argc, char **argv)
 	char *cachefile = NULL;
 	importargs_t idata = { 0 };
 	char *endptr;
+	int load_meta_thresh = 0;
 
 	struct option long_options[] = {
 		{"rewind-to-checkpoint", no_argument, NULL, CHECKPOINT_OPT},
+		{"load-meta-thresh", required_argument, NULL, LOAD_META_THRESH_OPT},
 		{0, 0, 0, 0}
 	};
 
@@ -3122,6 +3125,15 @@ zpool_do_import(int argc, char **argv)
 		case CHECKPOINT_OPT:
 			flags |= ZFS_IMPORT_CHECKPOINT;
 			break;
+		case LOAD_META_THRESH_OPT:
+			errno = 0;
+			load_meta_thresh = strtoull(optarg, &endptr, 0);
+			if (errno != 0 || *endptr != '\0') {
+				(void) fprintf(stderr,
+				    gettext("invalid load-meta-thresh value\n"));
+				usage(B_FALSE);
+			}
+			break;
 		case ':':
 			(void) fprintf(stderr, gettext("missing argument for "
 			    "'%c' option\n"), optopt);
@@ -3172,6 +3184,10 @@ zpool_do_import(int argc, char **argv)
 	    rewind_policy) != 0)
 		goto error;
 
+	if (load_meta_thresh)
+		if (nvlist_add_uint64(policy, ZPOOL_LOAD_META_THRESH, load_meta_thresh) != 0)
+			goto error;
+
 	/* check argument count */
 	if (do_all) {
 		if (argc != 0) {

module/zfs/spa.c

@@ -2198,6 +2198,12 @@ spa_load_verify(spa_t *spa)
 		spa_load_note(spa, "spa_load_verify found %llu metadata errors "
 		    "and %llu data errors", (u_longlong_t)sle.sle_meta_count,
 		    (u_longlong_t)sle.sle_data_count);
+
+		// If the policy allows metadata errors, ignore the error returned by traverse_pool.
+		if (error == EINVAL && policy.zlp_maxmeta > 0 && sle.sle_meta_count <= policy.zlp_maxmeta) {
+			spa_load_note(spa, "spa_load_verify continuing even though there are metadata errors");
+			error = 0;
+		}
 	}
 
 	if (spa_load_verify_dryrun ||