file metadata via fs API (was: [GIT PULL] Filesystem Information)

[Miklos Szeredi]

On Wed, Aug 12, 2020 at 10:29 AM David Howells <dhowells at redhat.com> wrote:
>
> Miklos Szeredi <miklos at szeredi.hu> wrote:
>
> > Worried about performance?  Io-uring will allow you to do all those
> > five syscalls (or many more) with just one I/O submission.
>
> io_uring isn't going to help here.  We're talking about synchronous reads.
> AIUI, you're adding a couple more syscalls to the list and running stuff in a
> side thread to save the effort of going in and out of the kernel five times.
> But you still have to pay the set up/tear down costs on the fds and do the
> pathwalks.  io_uring doesn't magically make that cost disappear.
>
> io_uring also requires resources such as a kernel accessible ring buffer to
> make it work.
>
> You're proposing making everything else more messy just to avoid a dedicated
> syscall.  Could you please set out your reasoning for that?

a) A dedicated syscall with a complex binary API is a non-trivial
maintenance burden.

b) The awarded performance boost is not warranted for the use cases it
is designed for.

Thanks,
Miklos