Fix unchecked return values and unused return values

Coverity complained about unchecked return values and unused values that
turned out to be unused return values.

Different approaches were used to handle the different cases of
unchecked return values:

* cmd/zdb/zdb.c: VERIFY0 was used in one place since the existing code
  had no error handling. An error message was printed in another to
  match the rest of the code.

* cmd/zed/agents/zfs_retire.c: We dismiss the return value with `(void)`
  because the value is expected to be potentially unset.

* cmd/zpool_influxdb/zpool_influxdb.c: We dismiss the return value with
  `(void)` because the values are expected to be potentially unset.

* cmd/ztest.c: VERIFY0 was used since we want failures if something goes
  wrong in ztest.

* module/zfs/dsl_dir.c: We dismiss the return value with `(void)`
  because there is no guarantee that the zap entry will always be there.
  For example, old pools imported readonly would not have it and we do
  not want to fail here because of that.

* module/zfs/zfs_fm.c: `fnvlist_add_*()` was used since the
  allocations sleep and thus can never fail.

* module/zfs/zvol.c: We dismiss the return value with `(void)` because
  we do not need it. This matches what is already done in the analogous
  `zfs_replay_write2()`.

* tests/zfs-tests/cmd/draid.c: We suppress one return value with
  `(void)` since the code handles errors already. The other return value
  is handled by switching to `fnvlist_lookup_uint8_array()`.

* tests/zfs-tests/cmd/file/file_fadvise.c: We add error handling.

* tests/zfs-tests/cmd/mmap_sync.c: We add error handling for munmap, but
  ignore failures on remove() with (void) since it is expected to be
  able to fail.

* tests/zfs-tests/cmd/mmapwrite.c: We add error handling.

As for unused return values, they were all in places where there was
error handling, so logic was added to handle the return values.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13920

cmd/zdb/zdb.c

@@ -4418,9 +4418,14 @@ dump_l2arc_log_blocks(int fd, l2arc_dev_hdr_phys_t l2dhdr,
 		default:
 			abd = abd_alloc_for_io(asize, B_TRUE);
 			abd_copy_from_buf_off(abd, &this_lb, 0, asize);
-			zio_decompress_data(L2BLK_GET_COMPRESS(
+			if (zio_decompress_data(L2BLK_GET_COMPRESS(
 			    (&lbps[0])->lbp_prop), abd, &this_lb,
-			    asize, sizeof (this_lb), NULL);
+			    asize, sizeof (this_lb), NULL) != 0) {
+				(void) printf("L2ARC block decompression "
+				    "failed\n");
+				abd_free(abd);
+				goto out;
+			}
 			abd_free(abd);
 			break;
 		}
@@ -4455,7 +4460,7 @@ dump_l2arc_log_blocks(int fd, l2arc_dev_hdr_phys_t l2dhdr,
 		lbps[0] = lbps[1];
 		lbps[1] = this_lb.lb_prev_lbp;
 	}
-
+out:
 	if (!dump_opt['q']) {
 		(void) printf("log_blk_count:\t %llu with valid cksum\n",
 		    (u_longlong_t)rebuild->dh_lb_count);
@@ -7586,7 +7591,7 @@ dump_mos_leaks(spa_t *spa)
 		} else {
 			dmu_object_info_t doi;
 			const char *name;
-			dmu_object_info(mos, object, &doi);
+			VERIFY0(dmu_object_info(mos, object, &doi));
 			if (doi.doi_type & DMU_OT_NEWTYPE) {
 				dmu_object_byteswap_t bswap =
 				    DMU_OT_BYTESWAP(doi.doi_type);
@@ -8698,6 +8703,8 @@ main(int argc, char **argv)
 			usage();
 		dump_opt['v'] = verbose;
 		error = dump_path(argv[0], argv[1], &object);
+		if (error != 0)
+			fatal("internal error: %s", strerror(error));
 	}
 
 	if (dump_opt['X'] || dump_opt['F'])

cmd/zed/agents/zfs_retire.c

@@ -326,7 +326,8 @@ zfs_retire_recv(fmd_hdl_t *hdl, fmd_event_t *ep, nvlist_t *nvl,
 
 	fmd_hdl_debug(hdl, "zfs_retire_recv: '%s'", class);
 
-	nvlist_lookup_uint64(nvl, FM_EREPORT_PAYLOAD_ZFS_VDEV_STATE, &state);
+	(void) nvlist_lookup_uint64(nvl, FM_EREPORT_PAYLOAD_ZFS_VDEV_STATE,
+	    &state);
 
 	/*
 	 * If this is a resource notifying us of device removal then simply

cmd/zpool_influxdb/zpool_influxdb.c

@@ -265,7 +265,7 @@ get_vdev_name(nvlist_t *nvroot, const char *parent_name)
 	uint64_t vdev_id = 0;
 
 	char *vdev_type = (char *)"unknown";
-	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
+	(void) nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
 
 	if (nvlist_lookup_uint64(
 	    nvroot, ZPOOL_CONFIG_ID, &vdev_id) != 0)
@@ -302,9 +302,9 @@ get_vdev_desc(nvlist_t *nvroot, const char *parent_name)
 	char *vdev_type = (char *)"unknown";
 	uint64_t vdev_id = UINT64_MAX;
 	char *vdev_path = NULL;
-	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
-	nvlist_lookup_uint64(nvroot, ZPOOL_CONFIG_ID, &vdev_id);
-	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_PATH, &vdev_path);
+	(void) nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
+	(void) nvlist_lookup_uint64(nvroot, ZPOOL_CONFIG_ID, &vdev_id);
+	(void) nvlist_lookup_string(nvroot, ZPOOL_CONFIG_PATH, &vdev_path);
 
 	if (parent_name == NULL) {
 		s = escape_string(vdev_type);

cmd/ztest.c

@@ -2214,7 +2214,7 @@ ztest_replay_write(void *arg1, void *arg2, boolean_t byteswap)
 		dmu_write(os, lr->lr_foid, offset, length, data, tx);
 	} else {
 		memcpy(abuf->b_data, data, length);
-		dmu_assign_arcbuf_by_dbuf(db, offset, abuf, tx);
+		VERIFY0(dmu_assign_arcbuf_by_dbuf(db, offset, abuf, tx));
 	}
 
 	(void) ztest_log_write(zd, tx, lr);

lib/libzfsbootenv/lzbe_device.c

@@ -74,6 +74,7 @@ lzbe_set_boot_device(const char *pool, lzbe_flags_t flag, const char *device)
 	/* version is mandatory */
 	fnvlist_add_uint64(nv, BOOTENV_VERSION, VB_NVLIST);
 
+	rv = 0;
 	/*
 	 * If device name is empty, remove boot device configuration.
 	 */
@@ -95,7 +96,7 @@ lzbe_set_boot_device(const char *pool, lzbe_flags_t flag, const char *device)
 				rv = ENOMEM;
 		}
 	}
-
+	if (rv == 0)
 		rv = zpool_set_bootenv(zphdl, nv);
 	if (rv != 0)
 		fprintf(stderr, "%s\n", libzfs_error_description(hdl));

module/zfs/dmu_recv.c

@@ -1874,6 +1874,8 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 	if (err == 0) {
 		err = receive_handle_existing_object(rwa, drro, &doi, data,
 		    &object_to_hold, &new_blksz);
+		if (err != 0)
+			return (err);
 	} else if (err == EEXIST) {
 		/*
 		 * The object requested is currently an interior slot of a

module/zfs/dsl_dataset.c

@@ -640,6 +640,8 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, const void *tag,
 				    dsl_dataset_phys(ds)->ds_prev_snap_obj,
 				    ds, &ds->ds_prev);
 			}
+			if (err != 0)
+				goto after_dsl_bookmark_fini;
 			err = dsl_bookmark_init_ds(ds);
 		} else {
 			if (zfs_flags & ZFS_DEBUG_SNAPNAMES)
@@ -688,11 +690,11 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, const void *tag,
 			winner = dmu_buf_set_user_ie(dbuf, &ds->ds_dbu);
 
 		if (err != 0 || winner != NULL) {
-			bplist_destroy(&ds->ds_pending_deadlist);
 			dsl_deadlist_close(&ds->ds_deadlist);
 			if (dsl_deadlist_is_open(&ds->ds_remap_deadlist))
 				dsl_deadlist_close(&ds->ds_remap_deadlist);
 			dsl_bookmark_fini_ds(ds);
+after_dsl_bookmark_fini:
 			if (ds->ds_prev)
 				dsl_dataset_rele(ds->ds_prev, ds);
 			dsl_dir_rele(ds->ds_dir, ds);
@@ -703,6 +705,7 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, const void *tag,
 
 			list_destroy(&ds->ds_prop_cbs);
 			list_destroy(&ds->ds_sendstreams);
+			bplist_destroy(&ds->ds_pending_deadlist);
 			mutex_destroy(&ds->ds_lock);
 			mutex_destroy(&ds->ds_opening_lock);
 			mutex_destroy(&ds->ds_sendstream_lock);

module/zfs/dsl_dir.c

@@ -270,7 +270,7 @@ dsl_dir_hold_obj(dsl_pool_t *dp, uint64_t ddobj,
 
 		if (dsl_dir_is_zapified(dd)) {
 			inode_timespec_t t = {0};
-			zap_lookup(dp->dp_meta_objset, ddobj,
+			(void) zap_lookup(dp->dp_meta_objset, ddobj,
 			    DD_FIELD_SNAPSHOTS_CHANGED,
 			    sizeof (uint64_t),
 			    sizeof (inode_timespec_t) / sizeof (uint64_t),

module/zfs/zfs_fm.c

@@ -1389,17 +1389,17 @@ zfs_post_state_change(spa_t *spa, vdev_t *vd, uint64_t laststate)
 	aux = fm_nvlist_create(NULL);
 	if (vd && aux) {
 		if (vd->vdev_physpath) {
-			(void) nvlist_add_string(aux,
+			fnvlist_add_string(aux,
 			    FM_EREPORT_PAYLOAD_ZFS_VDEV_PHYSPATH,
 			    vd->vdev_physpath);
 		}
 		if (vd->vdev_enc_sysfs_path) {
-			(void) nvlist_add_string(aux,
+			fnvlist_add_string(aux,
 			    FM_EREPORT_PAYLOAD_ZFS_VDEV_ENC_SYSFS_PATH,
 			    vd->vdev_enc_sysfs_path);
 		}
 
-		(void) nvlist_add_uint64(aux,
+		fnvlist_add_uint64(aux,
 		    FM_EREPORT_PAYLOAD_ZFS_VDEV_LASTSTATE, laststate);
 	}
 
@@ -1496,12 +1496,12 @@ zfs_ereport_zvol_post(const char *subclass, const char *name,
 		return;
 
 	aux = fm_nvlist_create(NULL);
-	nvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_DEVICE_NAME, dev_name);
-	nvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_RAW_DEVICE_NAME,
+	fnvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_DEVICE_NAME, dev_name);
+	fnvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_RAW_DEVICE_NAME,
 	    raw_name);
 	r = strchr(name, '/');
 	if (r && r[1])
-		nvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_VOLUME, &r[1]);
+		fnvlist_add_string(aux, FM_EREPORT_PAYLOAD_ZFS_VOLUME, &r[1]);
 
 	zfs_post_common(spa, NULL, FM_RSRC_CLASS, subclass, aux);
 	fm_nvlist_destroy(aux, FM_NVA_FREE);

module/zfs/zvol.c

@@ -429,7 +429,7 @@ zvol_replay_truncate(void *arg1, void *arg2, boolean_t byteswap)
 	if (error != 0) {
 		dmu_tx_abort(tx);
 	} else {
-		zil_replaying(zv->zv_zilog, tx);
+		(void) zil_replaying(zv->zv_zilog, tx);
 		dmu_tx_commit(tx);
 		error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset,
 		    length);
@@ -475,7 +475,7 @@ zvol_replay_write(void *arg1, void *arg2, boolean_t byteswap)
 		dmu_tx_abort(tx);
 	} else {
 		dmu_write(os, ZVOL_OBJ, offset, length, data, tx);
-		zil_replaying(zv->zv_zilog, tx);
+		(void) zil_replaying(zv->zv_zilog, tx);
 		dmu_tx_commit(tx);
 	}
 

tests/zfs-tests/cmd/draid.c

@@ -139,7 +139,7 @@ read_map_key(const char *filename, const char *key, nvlist_t **cfg)
 	if (error != 0)
 		return (error);
 
-	nvlist_lookup_nvlist(allcfgs, key, &foundcfg);
+	(void) nvlist_lookup_nvlist(allcfgs, key, &foundcfg);
 	if (foundcfg != NULL) {
 		nvlist_dup(foundcfg, cfg, KM_SLEEP);
 		error = 0;
@@ -375,7 +375,7 @@ dump_map_nv(const char *key, nvlist_t *cfg, int verbose)
 	map.dm_checksum = fnvlist_lookup_uint64(cfg, MAP_CHECKSUM);
 	map.dm_children = fnvlist_lookup_uint64(cfg, MAP_CHILDREN);
 	map.dm_nperms = fnvlist_lookup_uint64(cfg, MAP_NPERMS);
-	nvlist_lookup_uint8_array(cfg, MAP_PERMS, &map.dm_perms, &c);
+	map.dm_perms = fnvlist_lookup_uint8_array(cfg, MAP_PERMS, &c);
 
 	dump_map(&map, key, (double)worst_ratio / 1000.0,
 	    avg_ratio / 1000.0, verbose);

tests/zfs-tests/cmd/file/file_fadvise.c

@@ -89,7 +89,11 @@ main(int argc, char *argv[])
 		return (1);
 	}
 
-	posix_fadvise(fd, 0, 0, advise);
+	if (posix_fadvise(fd, 0, 0, advise) != 0) {
+		perror("posix_fadvise");
+		close(fd);
+		return (1);
+	}
 
 	close(fd);
 

tests/zfs-tests/cmd/mmap_sync.c

@@ -32,7 +32,7 @@
 static void
 cleanup(char *file)
 {
-	remove(file);
+	(void) remove(file);
 }
 
 int
@@ -125,7 +125,8 @@ main(int argc, char *argv[])
 		elapsed += ((t2.tv_usec - t1.tv_usec) / 1000.0);
 		if (elapsed > max_msync_time_ms) {
 			fprintf(stderr, "slow msync: %f ms\n", elapsed);
-			munmap(ptr, LEN);
+			if (munmap(ptr, LEN) != 0)
+				perror("munmap");
 			cleanup(file);
 			return (1);
 		}

tests/zfs-tests/cmd/mmapwrite.c

@@ -73,7 +73,11 @@ normal_writer(void *filename)
 			err(1, "write failed!");
 			break;
 		}
-		lseek(fd, page_size, SEEK_CUR);
+		if (lseek(fd, page_size, SEEK_CUR) == -1) {
+			err(1, "lseek failed on %s: %s", file_path,
+			    strerror(errno));
+			break;
+		}
 	}
 }