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Date: Wed, 12 Feb 2014 13:13:14 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Fabian Frederick <fabf@skynet.be>
Cc: linux-kernel@vger.kernel.org, rdunlap <rdunlap@infradead.org>
Subject: Re: [RFC 2/2] Arch: Kconfig: Disable obsolete syscalls
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On Wed, 12 Feb 2014 21:04:40 +0800 Fabian Frederick <fabf@skynet.be> wrote:

> fs: sysfs syscall: Disable if DISABLE_OBSOLETE_SYSCALLS
> 
> sysfs syscall is obsolete (cf man sysfs).
> 
> Don't define fs_index, fs_name, fs_maxindex functions when
> DISABLE_OBSOLETE_SYSCALLS is defined.
> In that case, SYSCALL_DEFINE3(sysfs...) returns automatically -EINVAL.
> 

Are there any other syscalls which will fall under
CONFIG_DISABLE_OBSOLETE_SYSCALLS?

There are plenty of other syscalls which can be disabled via Kconfig. 
As far as I recall, they each use their own CONFIG_foo.

So I'm thinking it would be better to add a CONFIG_SYS_SYSFS or
whatever which enables this syscall only.  It defaults to y.

> --- a/fs/filesystems.c
> +++ b/fs/filesystems.c
> @@ -121,6 +121,7 @@ int unregister_filesystem(struct file_system_type * fs)
>  
>  EXPORT_SYMBOL(unregister_filesystem);
>  
> +#ifndef CONFIG_DISABLE_OBSOLETE_SYSCALLS
>  static int fs_index(const char __user * __name)
>  {
>  	struct file_system_type * tmp;
> @@ -199,6 +200,12 @@ SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
>  	}
>  	return retval;
>  }
> +#else
> +SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
> +{
> +	return -EINVAL;
> +}
> +#endif /*CONFIG_DISABLE_OBSOLETE_SYSCALLS*/

And this should be done in kernel/sys_ni.c along with all the others.