lock-util: Add LOCK_NONE

src/basic/fs-util.c

@@ -1177,7 +1177,7 @@ int xopenat_lock(
 
         /* POSIX/UNPOSIX locks don't work on directories (errno is set to -EBADF so let's return early with
          * the same error here). */
-        if (FLAGS_SET(open_flags, O_DIRECTORY) && locktype != LOCK_BSD)
+        if (FLAGS_SET(open_flags, O_DIRECTORY) && !IN_SET(locktype, LOCK_BSD, LOCK_NONE))
                 return -EBADF;
 
         for (;;) {

src/basic/lock-util.c

@@ -174,6 +174,8 @@ int lock_generic(int fd, LockType type, int operation) {
         assert(fd >= 0);
 
         switch (type) {
+        case LOCK_NONE:
+                return 0;
         case LOCK_BSD:
                 return RET_NERRNO(flock(fd, operation));
         case LOCK_POSIX:

src/basic/lock-util.h

@@ -34,6 +34,7 @@ void unposix_unlockpp(int **fd);
         _cleanup_(unposix_unlockpp) _unused_ int *CONCATENATE(_cleanup_unposix_unlock_, UNIQ) = &(fd)
 
 typedef enum LockType {
+        LOCK_NONE, /* Don't lock the file descriptor. Useful if you need to conditionally lock a file. */
         LOCK_BSD,
         LOCK_POSIX,
         LOCK_UNPOSIX,