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> > > > ... > > > > close(pidfd); > > > > Or the equivalent call opening /proc/self. It is more convenient to use a > > sentinel value to indicate to an interface that accepts a pidfd that we > > simply wish to refer to the current process thread. > > > > The above code sequence doesn't seem at all onerous. I'm not > understanding why it's worth altering the kernel to permit this little > shortcut? In practice it adds quite a bit of overhead for something that whatever mechanism is using the pidfd can avoid. It was specifically intended for a real case of utilising process_madvise(), using the newly extended ability to batch _any_ madvise() operations for the current process, like: if (process_madvise(PIDFD_SELF, iovec, 10, MADV_GUARD_INSTALL, 0)) { ... error handling ... } vs. pid_t pid = getpid(); int pidfd = pidfd_open(pid, PIDFD_THREAD); if (pidfd < 0) { ... error handling ... } if (process_madvise(PIDFD_SELF, iovec, 10, MADV_GUARD_INSTALL, 0)) { ... cleanup pidfd ... ... error handling ... } ... ... cleanup pidfd ... So in practice, it's actually a lot more ceremony and noise. Suren has been working with this code in practice and found this to be useful. The suggestion to embed it as PIDFD_SELF rather than to pass it as a process_madvise() flag was made on the original series where I extended its functionality. So in practice I think it's onerous enough to justify this, plus it allows for a more fluent use of pidfd's in other cases where one is referring to the same process/thread, to the extent that I've seen people commenting on supporting it while sending series relating to pidfd. Also Christian and others appear to support this idea.