On Thu, May 18, 2023 at 10:20 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > That's just completely weird. We can see what Linus thinks but I think > that's a somewhat outlandish proposal that I wouldn't support. I have no idea of the background here. But fd 0 is in absolutely no way special. Anything that thinks that a zero fd is invalid or in any way different from (say) fd 5 is completely and utterly buggy by definition. Now, fd 0 can obviously be invalid in the sense that it may not be open, exactly the same way fd 100 may not be open. So in *that* sense we can have an invalid fd 0, and system calls might return EBADF for trying to access it if somebody has closed it. If bpf thinks that 0 is not a file descriptor, then bpf is simply wrong. No ifs, buts or maybes about it. It's like saying "1 is not a number". It's nonsensical garbage. But maybe I misunderstand the issue. Linus