linux-kernel - Re: [PATCH] fcntl.h: define AT

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Date:	Mon, 19 Apr 2010 14:47:29 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	maximilian attems <max@...o.at>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Ulrich Drepper <drepper@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [PATCH] fcntl.h: define AT_EACCESS

On Fri, 16 Apr 2010 05:08:00 +0200
maximilian attems <max@...o.at> wrote:

> noticed on a klibc build of dash that someone had left out that def:
> usr/dash/bltin/test.c:490: error: ___AT_EACCESS___ undeclared (first use in thiction)
> 
> Cc: stable@...nel.org
> Cc: Ulrich Drepper <drepper@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Signed-off-by: maximilian attems <max@...o.at>
> ---
>  include/linux/fcntl.h |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
> index 8603740..8bb001d 100644
> --- a/include/linux/fcntl.h
> +++ b/include/linux/fcntl.h
> @@ -39,6 +39,8 @@
>  #define AT_REMOVEDIR		0x200   /* Remove directory instead of
>                                             unlinking file.  */
>  #define AT_SYMLINK_FOLLOW	0x400   /* Follow symbolic links.  */
> +#define AT_EACCESS		0x200	/* Test access permitted for
> +					   effective IDs, not real IDs.  */
>  

I'm all confused.

The affects sys_faccesat(), yes?  But sys_faccesat() never gets passed
a `flags' argument so how does the behaviour which the FACCESSAT(2)
manpage describes get implemented?

This patch doesn't actually change kernel behaviour, so how can setting
AT_EACCESS change any syscall's actions?

It's a bit of a worry that the proposed value for AT_EACCESS duplicates
AT_REMOVEDIR.  I guess that, despite apeparances, they're different
namespaces.  Any thoughts on the implications of this?

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