systemd-mount: allow to specify an arbitrary string for arg_mount_what when vfs is used

Fixes #6591.

src/basic/mount-util.c

@@ -552,6 +552,32 @@ bool fstype_is_network(const char *fstype) {
         return nulstr_contains(table, fstype);
 }
 
+bool fstype_is_api_vfs(const char *fstype) {
+        static const char table[] =
+                "autofs\0"
+                "bpf\0"
+                "cgroup\0"
+                "cgroup2\0"
+                "configfs\0"
+                "cpuset\0"
+                "debugfs\0"
+                "devpts\0"
+                "devtmpfs\0"
+                "efivarfs\0"
+                "hugetlbfs\0"
+                "mqueue\0"
+                "proc\0"
+                "pstore\0"
+                "ramfs\0"
+                "securityfs\0"
+                "sysfs\0"
+                "tmpfs\0"
+                "tracefs\0"
+                ;
+
+        return nulstr_contains(table, fstype);
+}
+
 int repeat_unmount(const char *path, int flags) {
         bool done = false;
 

src/basic/mount-util.h

@@ -44,6 +44,7 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(FILE*, endmntent);
 #define _cleanup_endmntent_ _cleanup_(endmntentp)
 
 bool fstype_is_network(const char *fstype);
+bool fstype_is_api_vfs(const char *fstype);
 
 union file_handle_union {
         struct file_handle handle;