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Date: Sat, 7 Oct 2023 17:09:27 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH v2] pass AT_NO_AUTOMOUNT when emulating fstatat
via statx
On Sat, Oct 07, 2023 at 09:02:18PM +0300, Alexey Izbyshev wrote:
> AT_NO_AUTOMOUNT is implied for stat/lstat/fstatat syscalls since Linux
> 3.1 [1]. However, this is not the case for statx syscall, which defaults
> to automounting, so this flag must be passed explicitly when statx is
> used to implement stat-like functions.
>
> This change affects only arches which use 32-bit seconds in struct kstat,
> as well as out-of-tree/future ports to arches which lack SYS_fstatat.
>
> [1] https://git.kernel.org/torvalds/c/b6c8069d3577481390b3f24a8434ad72a3235594
> ---
> Fixed the wrong statement about affected arches in the commit message.
Indeed, statx is always used on 32-bit archs. 32-bit archs with no
legacy 32-bit kernel timespec struct (i.e. rv32) don't have the legacy
stat syscalls either.
> ---
> src/stat/fstatat.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/src/stat/fstatat.c b/src/stat/fstatat.c
> index 04506375d897..9eed063b26bc 100644
> --- a/src/stat/fstatat.c
> +++ b/src/stat/fstatat.c
> @@ -36,6 +36,7 @@ static int fstatat_statx(int fd, const char *restrict path, struct stat *restric
> {
> struct statx stx;
>
> + flag |= AT_NO_AUTOMOUNT;
> int ret = __syscall(SYS_statx, fd, path, flag, 0x7ff, &stx);
> if (ret) return ret;
>
> --
> 2.39.2
I think this is ok. I recall noticing something about this when
initially adding it but not being sure what behavior the legacy stat
syscall would give or whether it's "right". But short of a very good
reason to differ from the kernel default (which would then require
changing other archs to match), I think we just need to make it
consistent with what happens on other archs.
Rich
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