libzfs: pool: zpool_vdev_name: use libzfs_envvar_is_set

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#13413

lib/libzfs/libzfs_pool.c

@@ -4122,10 +4122,10 @@ char *
 zpool_vdev_name(libzfs_handle_t *hdl, zpool_handle_t *zhp, nvlist_t *nv,
     int name_flags)
 {
-	char *path, *type, *env;
+	char *path, *type;
 	uint64_t value;
 	char buf[PATH_BUF_LEN];
-	char tmpbuf[PATH_BUF_LEN];
+	char tmpbuf[PATH_BUF_LEN * 2];
 
 	/*
 	 * vdev_name will be "root"/"root-0" for the root vdev, but it is the
@@ -4135,19 +4135,11 @@ zpool_vdev_name(libzfs_handle_t *hdl, zpool_handle_t *zhp, nvlist_t *nv,
 	if (zhp != NULL && strcmp(type, "root") == 0)
 		return (zfs_strdup(hdl, zpool_get_name(zhp)));
 
-	env = getenv("ZPOOL_VDEV_NAME_PATH");
-	if (env && (strtoul(env, NULL, 0) > 0 ||
-	    !strncasecmp(env, "YES", 3) || !strncasecmp(env, "ON", 2)))
+	if (libzfs_envvar_is_set("ZPOOL_VDEV_NAME_PATH"))
 		name_flags |= VDEV_NAME_PATH;
-
-	env = getenv("ZPOOL_VDEV_NAME_GUID");
-	if (env && (strtoul(env, NULL, 0) > 0 ||
-	    !strncasecmp(env, "YES", 3) || !strncasecmp(env, "ON", 2)))
+	if (libzfs_envvar_is_set("ZPOOL_VDEV_NAME_GUID"))
 		name_flags |= VDEV_NAME_GUID;
-
-	env = getenv("ZPOOL_VDEV_NAME_FOLLOW_LINKS");
-	if (env && (strtoul(env, NULL, 0) > 0 ||
-	    !strncasecmp(env, "YES", 3) || !strncasecmp(env, "ON", 2)))
+	if (libzfs_envvar_is_set("ZPOOL_VDEV_NAME_FOLLOW_LINKS"))
 		name_flags |= VDEV_NAME_FOLLOW_LINKS;
 
 	if (nvlist_lookup_uint64(nv, ZPOOL_CONFIG_NOT_PRESENT, &value) == 0 ||