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

[Miklos Szeredi]

On Wed, Aug 12, 2020 at 2:05 AM David Howells <dhowells at redhat.com> wrote:

> >   {
> >      int fd, attrfd;
> >
> >      fd = open(path, O_PATH);
> >      attrfd = openat(fd, name, O_ALT);
> >      close(fd);
> >      read(attrfd, value, size);
> >      close(attrfd);
> >   }
>
> Please don't go down this path.  You're proposing five syscalls - including
> creating two file descriptors - to do what fsinfo() does in one.

So what?  People argued against readfile() for exactly the opposite of
reasons, even though that's a lot less specialized than fsinfo().

Worried about performance?  Io-uring will allow you to do all those
five syscalls (or many more) with just one I/O submission.

Thanks,
Miklos