linux-kernel - Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY

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Message-ID: <CAAhV-H5n-6AjPuMj6sH0T2uSy97LMy3qkimUT13S2Fi-p-6Nug@mail.gmail.com>
Date: Wed, 3 Jul 2024 12:30:06 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Xi Ruoyao <xry111@...111.site>, Mateusz Guzik <mjguzik@...il.com>, 
	Christian Brauner <brauner@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, loongarch@...ts.linux.dev
Subject: Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)

On Wed, Jul 3, 2024 at 1:07 AM Arnd Bergmann <arnd@...db.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@...db.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