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

[Miklos Szeredi]

On Tue, Aug 11, 2020 at 5:20 PM Linus Torvalds
<torvalds at linux-foundation.org> wrote:
>
> [ I missed the beginning of this discussion, so maybe this was already
> suggested ]
>
> On Tue, Aug 11, 2020 at 6:54 AM Miklos Szeredi <miklos at szeredi.hu> wrote:
> >
> > >
> > > E.g.
> > >   openat(AT_FDCWD, "foo/bar//mnt/info", O_RDONLY | O_ALT);
> >
> > Proof of concept patch and test program below.
>
> I don't think this works for the reasons Al says, but a slight
> modification might.
>
> IOW, if you do something more along the lines of
>
>        fd = open(""foo/bar", O_PATH);
>        metadatafd = openat(fd, "metadataname", O_ALT);
>
> it might be workable.

That would have been my backup suggestion, in case the unified
namespace doesn't work out.

I wouldn't think the normal lookup rules really get in the way if we
explicitly enable alternative path lookup with a flag.  The rules just
need to be documented.

What's the disadvantage of doing it with a single lookup WITH an enabling flag?

It's definitely not going to break anything, so no backward
compatibility issues whatsoever.

Thanks,
Miklos