Re: fd == 0 means AT_FDCWD BPF_OBJ_GET commands

Christoph Hellwig
2023-05-17T12:05:42Z

On Wed, May 17, 2023 at 11:11:24AM +0200, Christian Brauner wrote:
> Adding fsdevel so we're aware of this quirk.
>
> So I'm not sure whether this was ever discussed on fsdevel when you took
> the decision to treat fd 0 as AT_FDCWD or in general treat fd 0 as an
> invalid value.

I've never heard of this before, and I think it is compltely
unacceptable. 0 ist just a normal FD, although one that happens to
have specific meaning in userspace as stdin.

>
> If it was discussed then great but if not then I would like to make it
> very clear that if in the future you decide to introduce custom
> semantics for vfs provided infrastructure - especially when exposed to
> userspace - that you please Cc us.

I don't think it's just the future. We really need to undo this ASAP.