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

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Message-ID: <fa1a8a0b01cd8c53d290cf431b9c1ffc6305ef0d.camel@xry111.site>
Date: Tue, 25 Jun 2024 21:24:32 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Mateusz Guzik <mjguzik@...il.com>, brauner@...nel.org
Cc: 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, 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.

> +		return do_statx_fd(dfd, flags, mask, buffer);
> +
>  	name = getname_flags(filename, getname_statx_lookup_flags(flags), NULL);

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University