QLockFile of size 0

It seems to be possible to create a lockfile of size 0 which is not deleted in the constructor:

In QLockFilePrivate::tryLock_sys() qt_safe_open can succeed and the subsequent can qt_write_loop can fail. As a result t->isLocked will stay at 'false' (that's correct), but the 'unlock' in the destructor will return early without removing the empty file.

I believe in addition to the "error = QLockFile::UnknownError; // partition full" line there should be QFile::remove(d->fileName) or similar to clean up.