Handle d_type == DT_UNKNOWN correctly

As documented in the man-page, readdir() may return a directory entry with
d_type == DT_UNKNOWN. This must be handled for regular filesystems.

dirent_ensure_type() is available to set d_type if necessary. Use it in
some more places.

Without this systemd will fail to boot correctly with nfsroot and some
other filesystems.

Closes #13609

src/core/smack-setup.c

@@ -84,6 +84,7 @@ static int write_access2_rules(const char *srcdir) {
         FOREACH_DIRENT(entry, dir, return 0) {
                 _cleanup_fclose_ FILE *policy = NULL;
 
+                dirent_ensure_type(dir, entry);
                 if (!dirent_is_file(entry))
                         continue;
 
@@ -150,6 +151,7 @@ static int write_cipso2_rules(const char *srcdir) {
         FOREACH_DIRENT(entry, dir, return 0) {
                 _cleanup_fclose_ FILE *policy = NULL;
 
+                dirent_ensure_type(dir, entry);
                 if (!dirent_is_file(entry))
                         continue;
 

src/login/logind-dbus.c

@@ -1378,6 +1378,7 @@ static int flush_devices(Manager *m) {
                 struct dirent *de;
 
                 FOREACH_DIRENT_ALL(de, d, break) {
+                        dirent_ensure_type(d, de);
                         if (!dirent_is_file(de))
                                 continue;
 

src/login/logind.c

@@ -291,6 +291,7 @@ static int manager_enumerate_linger_users(Manager *m) {
         FOREACH_DIRENT(de, d, return -errno) {
                 int k;
 
+                dirent_ensure_type(d, de);
                 if (!dirent_is_file(de))
                         continue;
 

src/shared/bootspec.c

@@ -475,6 +475,7 @@ static int boot_entries_find_unified(
                 _cleanup_free_ char *j = NULL, *osrelease = NULL, *cmdline = NULL;
                 _cleanup_close_ int fd = -1;
 
+                dirent_ensure_type(d, de);
                 if (!dirent_is_file(de))
                         continue;
 

src/shared/unit-file.c

@@ -279,6 +279,7 @@ int unit_file_build_name_map(
                         if (hashmap_contains(ids, de->d_name))
                                 continue;
 
+                        dirent_ensure_type(d, de);
                         if (de->d_type == DT_LNK) {
                                 /* We don't explicitly check for alias loops here. unit_ids_map_get() which
                                  * limits the number of hops should be used to access the map. */