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

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Date: Tue, 25 Jun 2024 15:28:20 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Xi Ruoyao <xry111@...111.site>
Cc: brauner@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	io-uring@...r.kernel.org, axboe@...nel.dk, torvalds@...ux-foundation.org, 
	loongarch@...ts.linux.dev
Subject: Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)

On Tue, Jun 25, 2024 at 3:24 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> On Tue, 2024-06-25 at 13:00 +0200, Mateusz Guzik wrote:
> > +     if (flags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename))
>
> Could it be
>
> if ((flags & AT_EMPTY_PATH) && vfs_empty_path(dfd, filename))
>
> instead?
>
> When fstatat is implemented with statx AT_NO_AUTOMOUNT is needed, or at
> least Glibc developers think it's needed:
>
> #if FSTATAT_USE_STATX
>
> static inline int
> fstatat64_time64_statx (int fd, const char *file, struct __stat64_t64 *buf,
>             int flag)
> {
>   /* 32-bit kABI with default 64-bit time_t, e.g. arc, riscv32.   Also
>      64-bit time_t support is done through statx syscall.  */
>   struct statx tmp;
>   int r = INTERNAL_SYSCALL_CALL (statx, fd, file, AT_NO_AUTOMOUNT | flag,
>                  STATX_BASIC_STATS, &tmp);
>
> so "flags == AT_EMPTY_PATH" won't be true if Glibc implements fstatat
> and fstat via statx (on LoongArch and 32-bit platforms).
>
> I was just surprised when I saw a 100%+ improve for statx("",
> AT_EMPTY_PATH) but not stat on the Loongson machine.
>

It can't be like that specifically because we still need to catch
bogus AT flags.

I'm going to poke a little bit and send a v2, thanks.

-- 
Mateusz Guzik <mjguzik gmail.com>