Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)

[Huacai Chen <chenhuacai@kernel.org>]

On Wed, Jul 3, 2024 at 1:07 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Tue, Jul 2, 2024, at 17:36, Huacai Chen wrote:
> > On Mon, Jul 1, 2024 at 7:59 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >> On Sun, Jun 30, 2024, at 04:39, Xi Ruoyao wrote:
> >> > On Sun, 2024-06-30 at 09:40 +0800, Huacai Chen wrote:
> >> >> >
> >> >> > Yes, both Linus and Christian hates introducing a new AT_ flag for
> >> >> > this.
> >> >> >
> >> >> > This patch just makes statx(fd, NULL, AT_EMPTY_PATH, ...) behave
> >> >> > like
> >> >> > statx(fd, "", AT_EMPTY_PATH, ...) instead.  NULL avoids the
> >> >> > performance
> >> >> > issue and it's also audit-able by seccomp BPF.
> >> >> To be honest, I still want to restore __ARCH_WANT_NEW_STAT. Because
> >> >> even if statx() becomes audit-able, it is still blacklisted now.
> >> >
> >> > Then patch the sandbox to allow it.
> >> >
> >> > The sandbox **must** be patched anyway or it'll be broken on all 32-bit
> >> > systems after 2037.  [Unless they'll unsupport all 32-bit systems before
> >> > 2037.]
> >>
> >> More importantly, the sandbox won't be able to support any 32-bit
> >> targets that support running after 2037, regardless of how long
> >> the sandbox supports them: if you turn off COMPAT_32BIT_TIME today
> >> in order to be sure those don't get called by accident, the
> >> fallback is immediately broken.
> > Would you mind if I restore newstat for LoongArch64 even if this patch exist?
>
> I still prefer not add newstat back: it's easier to
> get applications to correctly implement the statx() code
> path if there are more architectures that only have that.
Yes, we need statx-only architecures to improve statx(), and so this
patch got upstream. But I'm considering bidirectional compatibility,
which means the kernel should work with future patched and existing
un-patched sandboxes. So I think now is the correct time to add
newstat back for LoongArch --- statx() has been improved, and existing
applications want to work on LoongArch.

Huacai

>
>        Arnd