linux-kernel - Re: [PATCH] vfs: Add AT_EMPTY_PATH_NOCHECK as unchecked AT_EMPTY

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Message-ID: <20240625-dinosaurier-keramik-f04310167065@brauner>
Date: Tue, 25 Jun 2024 10:05:47 +0200
From: Christian Brauner <brauner@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
Cc: Mateusz Guzik <mjguzik@...il.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Jan Kara <jack@...e.cz>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Alejandro Colomar <alx@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Huacai Chen <chenhuacai@...ngson.cn>, 
	Xuerui Wang <kernel@...0n.name>, Jiaxun Yang <jiaxun.yang@...goat.com>, 
	Icenowy Zheng <uwu@...nowy.me>, linux-fsdevel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-arch@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: Add AT_EMPTY_PATH_NOCHECK as unchecked AT_EMPTY_PATH

On Sat, Jun 22, 2024 at 03:41:19PM GMT, Linus Torvalds wrote:
> On Sat, 22 Jun 2024 at 14:25, Mateusz Guzik <mjguzik@...il.com> wrote:
> >
> > +cc Linus
> 
> Thanks.
> 
> > To sum up the problem: stat and statx met with "" + AT_EMPTY_PATH have
> > more work to do than fstat and its hypotethical statx counterpart:
> > - buf alloc/free for the path
> > - userspace access (very painful on x86_64 + SMAP)
> > - lockref acquire/release
> 
> Yes. That LOOKUP_EMPTY_NOCHECK is *not* the fix.

I have explicitly NAKed an approach like this months ago in [1]. So I'm
not sure why we're getting that patch in the first place tbh.

[1]: https://lore.kernel.org/lkml/599df4a3-47a4-49be-9c81-8e21ea1f988a@xen0n.name