linux-kernel - Re: [PATCH] sysctl: Deprecate sys_sysctl in a user space visible fashion.

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Date:	Sun, 02 Sep 2007 09:54:36 +0100
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rob Landley <rob@...dley.net>
CC:	Andi Kleen <andi@...stfloor.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysctl: Deprecate sys_sysctl in a user space visible
 fashion.

Rob Landley wrote:
> On Saturday 01 September 2007 5:16:03 pm Andi Kleen wrote:
>> Rob Landley <rob@...dley.net> writes:
>>> A lot of embedded people like to configure /proc out of the kernel for
>>> space reasons.  This would make that noticeably more painful.
>> I had a patch for a sysctl_name(2) for this a long time ago.
>> If it was a serious issue that could be reintroduced.
>>
>> BTW sysctl(2) only needs to be quiet for a single sysctl used
>> by glibc.
>>
>> -Andi
> 
> Yeah, I found it:
> http://lkml.org/lkml/2003/7/10/345
> 
> I think that if /proc/sys could be broken out as a separate filesystem, and it 
> was small and simple, the embedded people would probably be happy.  Is your 
> patch significantly smaller than such a filesystem would be?  (Keeping in 
> mind that the smallest thing you can do is run from initramfs, and I think 
> that's pulling in libfs already...)
> 

IMO, the big problem with /proc/sys (and, for that matter, /sys) is 
mainly that they have to live in the process namespace, which is highly 
awkward when one uses chroot().

One way to solve *that* might be a system call to get a file descriptor 
to the root of sysfs or procsysfs which can be used with openat().  That 
has its own perils, of course...

	-hpa
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