Re: [PATCH v5 2/3] fs: openat2: Extend open_how to allow userspace-selected fds

[Miklos Szeredi]

On Wed, Apr 22, 2020 at 8:06 AM Michael Kerrisk (man-pages)
<mtk.manpages@xxxxxxxxx> wrote:
>
> [CC += linux-api]
>
> On Wed, 22 Apr 2020 at 07:20, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote:
> >
> > Inspired by the X protocol's handling of XIDs, allow userspace to select
> > the file descriptor opened by openat2, so that it can use the resulting
> > file descriptor in subsequent system calls without waiting for the
> > response to openat2.
> >
> > In io_uring, this allows sequences like openat2/read/close without
> > waiting for the openat2 to complete. Multiple such sequences can
> > overlap, as long as each uses a distinct file descriptor.

If this is primarily an io_uring feature, then why burden the normal
openat2 API with this?

Add this flag to the io_uring API, by all means.

This would also allow Implementing a private fd table for io_uring.
I.e. add a flag interpreted by file ops (IORING_PRIVATE_FD), including
openat2 and freely use the private fd space without having to worry
about interactions with other parts of the system.

Thanks,
Miklos