nvpair: Constify string functions

After addressing coverity complaints involving `nvpair_name()`, the
compiler started complaining about dropping const. This lead to a rabbit
hole where not only `nvpair_name()` needed to be constified, but also
`nvpair_value_string()`, `fnvpair_value_string()` and a few other static
functions, plus variable pointers throughout the code. The result became
a fairly big change, so it has been split out into its own patch.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes openzfs#14612

cmd/mount_zfs.c

@@ -74,7 +74,7 @@ parse_dataset(const char *target, char **dataset)
 
 	nvlist_t *cfg = NULL;
 	if (zpool_read_label(fd, &cfg, NULL) == 0) {
-		char *nm = NULL;
+		const char *nm = NULL;
 		if (!nvlist_lookup_string(cfg, ZPOOL_CONFIG_POOL_NAME, &nm))
 			strlcpy(*dataset, nm, PATH_MAX);
 		nvlist_free(cfg);

cmd/zdb/zdb.c

@@ -4215,7 +4215,7 @@ collect_nvlist_stats(nvlist_t *nvl, zdb_nvl_stats_t *stats)
 {
 	nvlist_t *list, **array;
 	nvpair_t *nvp = NULL;
-	char *name;
+	const char *name;
 	uint_t i, items;
 
 	stats->zns_list_count++;

cmd/zed/agents/fmd_api.c

@@ -359,7 +359,7 @@ static void
 zed_log_fault(nvlist_t *nvl, const char *uuid, const char *code)
 {
 	nvlist_t *rsrc;
-	char *strval;
+	const char *strval;
 	uint64_t guid;
 	uint8_t byte;
 
@@ -389,7 +389,7 @@ zed_log_fault(nvlist_t *nvl, const char *uuid, const char *code)
 static const char *
 fmd_fault_mkcode(nvlist_t *fault)
 {
-	char *class;
+	const char *class;
 	const char *code = "-";
 
 	/*
@@ -708,7 +708,7 @@ int
 fmd_nvl_class_match(fmd_hdl_t *hdl, nvlist_t *nvl, const char *pattern)
 {
 	(void) hdl;
-	char *class;
+	const char *class;
 
 	return (nvl != NULL &&
 	    nvlist_lookup_string(nvl, FM_CLASS, &class) == 0 &&

cmd/zed/agents/zfs_agents.c

@@ -64,7 +64,7 @@ typedef enum device_type {
 typedef struct guid_search {
 	uint64_t	gs_pool_guid;
 	uint64_t	gs_vdev_guid;
-	char		*gs_devid;
+	const char	*gs_devid;
 	device_type_t	gs_vdev_type;
 	uint64_t	gs_vdev_expandtime;	/* vdev expansion time */
 } guid_search_t;
@@ -77,7 +77,7 @@ static boolean_t
 zfs_agent_iter_vdev(zpool_handle_t *zhp, nvlist_t *nvl, void *arg)
 {
 	guid_search_t *gsp = arg;
-	char *path = NULL;
+	const char *path = NULL;
 	uint_t c, children;
 	nvlist_t **child;
 	uint64_t vdev_guid;
@@ -211,7 +211,7 @@ zfs_agent_post_event(const char *class, const char *subclass, nvlist_t *nvl)
 		uint64_t pool_guid = 0, vdev_guid = 0;
 		guid_search_t search = { 0 };
 		device_type_t devtype = DEVICE_TYPE_PRIMARY;
-		char *devid = NULL;
+		const char *devid = NULL;
 
 		class = "resource.fs.zfs.removed";
 		subclass = "";

cmd/zed/agents/zfs_diagnosis.c

@@ -464,7 +464,7 @@ zfs_fm_recv(fmd_hdl_t *hdl, fmd_event_t *ep, nvlist_t *nvl, const char *class)
 	nvlist_t *detector;
 	boolean_t pool_found = B_FALSE;
 	boolean_t isresource;
-	char *type;
+	const char *type;
 
 	/*
 	 * We subscribe to notifications for vdev or pool removal.  In these
@@ -780,7 +780,7 @@ zfs_fm_recv(fmd_hdl_t *hdl, fmd_event_t *ep, nvlist_t *nvl, const char *class)
 	    ZFS_MAKE_EREPORT(FM_EREPORT_ZFS_IO_FAILURE)) ||
 	    fmd_nvl_class_match(hdl, nvl,
 	    ZFS_MAKE_EREPORT(FM_EREPORT_ZFS_PROBE_FAILURE))) {
-		char *failmode = NULL;
+		const char *failmode = NULL;
 		boolean_t checkremove = B_FALSE;
 		uint32_t pri = 0;
 		int32_t flags = 0;

cmd/zed/agents/zfs_mod.c

@@ -183,15 +183,15 @@ zfs_unavail_pool(zpool_handle_t *zhp, void *data)
 static void
 zfs_process_add(zpool_handle_t *zhp, nvlist_t *vdev, boolean_t labeled)
 {
-	char *path;
+	const char *path;
 	vdev_state_t newstate;
 	nvlist_t *nvroot, *newvd;
 	pendingdev_t *device;
 	uint64_t wholedisk = 0ULL;
 	uint64_t offline = 0ULL, faulted = 0ULL;
 	uint64_t guid = 0ULL;
 	uint64_t is_spare = 0;
-	char *physpath = NULL, *new_devid = NULL, *enc_sysfs_path = NULL;
+	const char *physpath = NULL, *new_devid = NULL, *enc_sysfs_path = NULL;
 	char rawpath[PATH_MAX], fullpath[PATH_MAX];
 	char devpath[PATH_MAX];
 	int ret;
@@ -549,7 +549,7 @@ static void
 zfs_iter_vdev(zpool_handle_t *zhp, nvlist_t *nvl, void *data)
 {
 	dev_data_t *dp = data;
-	char *path = NULL;
+	const char *path = NULL;
 	uint_t c, children;
 	nvlist_t **child;
 	uint64_t guid = 0;
@@ -851,7 +851,7 @@ guid_iter(uint64_t pool_guid, uint64_t vdev_guid, const char *devid,
 static int
 zfs_deliver_add(nvlist_t *nvl)
 {
-	char *devpath = NULL, *devid = NULL;
+	const char *devpath = NULL, *devid = NULL;
 	uint64_t pool_guid = 0, vdev_guid = 0;
 	boolean_t is_slice;
 
@@ -999,7 +999,8 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 	nvlist_t *tgt;
 	int error;
 
-	char *tmp_devname, devname[MAXPATHLEN] = "";
+	const char *tmp_devname;
+	char devname[MAXPATHLEN] = "";
 	uint64_t guid;
 
 	if (nvlist_lookup_uint64(udev_nvl, ZFS_EV_VDEV_GUID, &guid) == 0) {
@@ -1017,7 +1018,8 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 
 	if ((tgt = zpool_find_vdev_by_physpath(zhp, devname,
 	    &avail_spare, &l2cache, NULL)) != NULL) {
-		char *path, fullpath[MAXPATHLEN];
+		const char *path;
+		char fullpath[MAXPATHLEN];
 		uint64_t wholedisk = 0;
 
 		error = nvlist_lookup_string(tgt, ZPOOL_CONFIG_PATH, &path);
@@ -1030,10 +1032,11 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 		    &wholedisk);
 
 		if (wholedisk) {
+			char *tmp;
 			path = strrchr(path, '/');
 			if (path != NULL) {
-				path = zfs_strip_partition(path + 1);
-				if (path == NULL) {
+				tmp = zfs_strip_partition(path + 1);
+				if (tmp == NULL) {
 					zpool_close(zhp);
 					return (0);
 				}
@@ -1042,8 +1045,8 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 				return (0);
 			}
 
-			(void) strlcpy(fullpath, path, sizeof (fullpath));
-			free(path);
+			(void) strlcpy(fullpath, tmp, sizeof (fullpath));
+			free(tmp);
 
 			/*
 			 * We need to reopen the pool associated with this
@@ -1148,7 +1151,8 @@ zfsdle_vdev_online(zpool_handle_t *zhp, void *data)
 static int
 zfs_deliver_dle(nvlist_t *nvl)
 {
-	char *devname, name[MAXPATHLEN];
+	const char *devname;
+	char name[MAXPATHLEN];
 	uint64_t guid;
 
 	if (nvlist_lookup_uint64(nvl, ZFS_EV_VDEV_GUID, &guid) == 0) {

cmd/zed/agents/zfs_retire.c

@@ -282,7 +282,7 @@ replace_with_spare(fmd_hdl_t *hdl, zpool_handle_t *zhp, nvlist_t *vdev)
 	 */
 	for (s = 0; s < nspares; s++) {
 		boolean_t rebuild = B_FALSE;
-		char *spare_name, *type;
+		const char *spare_name, *type;
 
 		if (nvlist_lookup_string(spares[s], ZPOOL_CONFIG_PATH,
 		    &spare_name) != 0)
@@ -377,9 +377,9 @@ zfs_retire_recv(fmd_hdl_t *hdl, fmd_event_t *ep, nvlist_t *nvl,
 	boolean_t is_repair;
 	boolean_t l2arc = B_FALSE;
 	boolean_t spare = B_FALSE;
-	char *scheme;
+	const char *scheme;
 	nvlist_t *vdev = NULL;
-	char *uuid;
+	const char *uuid;
 	int repair_done = 0;
 	boolean_t retire;
 	boolean_t is_disk;
@@ -401,7 +401,7 @@ zfs_retire_recv(fmd_hdl_t *hdl, fmd_event_t *ep, nvlist_t *nvl,
 	if (strcmp(class, "resource.fs.zfs.removed") == 0 ||
 	    (strcmp(class, "resource.fs.zfs.statechange") == 0 &&
 	    (state == VDEV_STATE_REMOVED || state == VDEV_STATE_FAULTED))) {
-		char *devtype;
+		const char *devtype;
 		char *devname;
 
 		if (nvlist_lookup_string(nvl, FM_EREPORT_PAYLOAD_ZFS_VDEV_TYPE,

cmd/zed/zed_disk_event.c

@@ -60,7 +60,7 @@ struct udev_monitor *g_mon;
 static void
 zed_udev_event(const char *class, const char *subclass, nvlist_t *nvl)
 {
-	char *strval;
+	const char *strval;
 	uint64_t numval;
 
 	zed_log_msg(LOG_INFO, "zed_disk_event:");
@@ -178,7 +178,8 @@ static void *
 zed_udev_monitor(void *arg)
 {
 	struct udev_monitor *mon = arg;
-	char *tmp, *tmp2;
+	const char *tmp;
+	char *tmp2;
 
 	zed_log_msg(LOG_INFO, "Waiting for new udev disk events...");
 
@@ -336,7 +337,7 @@ zed_udev_monitor(void *arg)
 		if (strcmp(class, EC_DEV_STATUS) == 0 &&
 		    udev_device_get_property_value(dev, "DM_UUID") &&
 		    udev_device_get_property_value(dev, "MPATH_SBIN_PATH")) {
-			tmp = (char *)udev_device_get_devnode(dev);
+			tmp = udev_device_get_devnode(dev);
 			tmp2 = zfs_get_underlying_path(tmp);
 			if (tmp && tmp2 && (strcmp(tmp, tmp2) != 0)) {
 				/*
@@ -353,8 +354,7 @@ zed_udev_monitor(void *arg)
 				class = EC_DEV_ADD;
 				subclass = ESC_DISK;
 			} else {
-				tmp = (char *)
-				    udev_device_get_property_value(dev,
+				tmp = udev_device_get_property_value(dev,
 				    "DM_NR_VALID_PATHS");
 				/* treat as a multipath remove */
 				if (tmp != NULL && strcmp(tmp, "0") == 0) {

cmd/zed/zed_event.c

@@ -612,7 +612,7 @@ _zed_event_add_string_array(uint64_t eid, zed_strings_t *zsp,
 	char buf[MAXBUF];
 	int buflen = sizeof (buf);
 	const char *name;
-	char **strp;
+	const char **strp;
 	uint_t nelem;
 	uint_t i;
 	char *p;
@@ -652,7 +652,7 @@ _zed_event_add_nvpair(uint64_t eid, zed_strings_t *zsp, nvpair_t *nvp)
 	uint16_t i16;
 	uint32_t i32;
 	uint64_t i64;
-	char *str;
+	const char *str;
 
 	assert(zsp != NULL);
 	assert(nvp != NULL);
@@ -935,7 +935,7 @@ zed_event_service(struct zed_conf *zcp)
 	uint64_t eid;
 	int64_t *etime;
 	uint_t nelem;
-	char *class;
+	const char *class;
 	const char *subclass;
 	int rv;
 

cmd/zfs/zfs_iter.c

@@ -348,7 +348,7 @@ zfs_sort(const void *larg, const void *rarg, void *data)
 
 	for (psc = sc; psc != NULL; psc = psc->sc_next) {
 		char lbuf[ZFS_MAXPROPLEN], rbuf[ZFS_MAXPROPLEN];
-		char *lstr, *rstr;
+		const char *lstr, *rstr;
 		uint64_t lnum = 0, rnum = 0;
 		boolean_t lvalid, rvalid;
 		int ret = 0;

cmd/zfs/zfs_main.c

@@ -1049,7 +1049,7 @@ zfs_do_create(int argc, char **argv)
 	int ret = 1;
 	nvlist_t *props;
 	uint64_t intval;
-	char *strval;
+	const char *strval;
 
 	if (nvlist_alloc(&props, NV_UNIQUE_NAME, 0) != 0)
 		nomem();
@@ -1173,11 +1173,12 @@ zfs_do_create(int argc, char **argv)
 
 		if (volblocksize != ZVOL_DEFAULT_BLOCKSIZE &&
 		    nvlist_lookup_string(props, prop, &strval) != 0) {
-			if (asprintf(&strval, "%llu",
+			char *tmp;
+			if (asprintf(&tmp, "%llu",
 			    (u_longlong_t)volblocksize) == -1)
 				nomem();
-			nvlist_add_string(props, prop, strval);
-			free(strval);
+			nvlist_add_string(props, prop, tmp);
+			free(tmp);
 		}
 
 		/*
@@ -1252,7 +1253,7 @@ zfs_do_create(int argc, char **argv)
 		    dryrun ? "would create %s\n" : "create %s\n", argv[0]);
 		while ((nvp = nvlist_next_nvpair(props, nvp)) != NULL) {
 			uint64_t uval;
-			char *sval;
+			const char *sval;
 
 			switch (nvpair_type(nvp)) {
 			case DATA_TYPE_UINT64:
@@ -2702,8 +2703,8 @@ us_compare(const void *larg, const void *rarg, void *unused)
 	boolean_t lvb, rvb;
 
 	for (; sortcol != NULL; sortcol = sortcol->sc_next) {
-		char *lvstr = (char *)"";
-		char *rvstr = (char *)"";
+		const char *lvstr = "";
+		const char *rvstr = "";
 		uint32_t lv32 = 0;
 		uint32_t rv32 = 0;
 		uint64_t lv64 = 0;
@@ -6499,7 +6500,7 @@ print_holds(boolean_t scripted, int nwidth, int tagwidth, nvlist_t *nvl,
 	}
 
 	while ((nvp = nvlist_next_nvpair(nvl, nvp)) != NULL) {
-		char *zname = nvpair_name(nvp);
+		const char *zname = nvpair_name(nvp);
 		nvlist_t *nvl2;
 		nvpair_t *nvp2 = NULL;
 		(void) nvpair_value_nvlist(nvp, &nvl2);
@@ -8119,7 +8120,7 @@ zfs_do_channel_program(int argc, char **argv)
 		const char *msg = gettext("Channel program execution failed");
 		uint64_t instructions = 0;
 		if (outnvl != NULL && nvlist_exists(outnvl, ZCP_RET_ERROR)) {
-			char *es = NULL;
+			const char *es = NULL;
 			(void) nvlist_lookup_string(outnvl,
 			    ZCP_RET_ERROR, &es);
 			if (es == NULL)

cmd/zpool/zpool_iter.c

@@ -564,9 +564,9 @@ for_each_vdev_run_cb(void *zhp_data, nvlist_t *nv, void *cb_vcdl)
 {
 	vdev_cmd_data_list_t *vcdl = cb_vcdl;
 	vdev_cmd_data_t *data;
-	char *path = NULL;
+	const char *path = NULL;
 	char *vname = NULL;
-	char *vdev_enc_sysfs_path = NULL;
+	const char *vdev_enc_sysfs_path = NULL;
 	int i, match = 0;
 	zpool_handle_t *zhp = zhp_data;