linux-kernel - Re: [PATCH 01/11] SYSCTL: export root and set handling routines

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Message-ID: <m1ehv76v2v.fsf@fess.ebiederm.org>
Date:	Tue, 10 Jan 2012 14:39:36 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"Trond.Myklebust\@netapp.com" <Trond.Myklebust@...app.com>,
	"linux-nfs\@vger.kernel.org" <linux-nfs@...r.kernel.org>,
	Pavel Emelianov <xemul@...allels.com>,
	"neilb\@suse.de" <neilb@...e.de>,
	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	James Bottomley <jbottomley@...allels.com>,
	"bfields\@fieldses.org" <bfields@...ldses.org>,
	"davem\@davemloft.net" <davem@...emloft.net>,
	"devel\@openvz.org" <devel@...nvz.org>
Subject: Re: [PATCH 01/11] SYSCTL: export root and set handling routines

Stanislav Kinsbursky <skinsbursky@...allels.com> writes:

> 03.01.2012 07:49, Eric W. Biederman пишет:
>> Stanislav Kinsbursky<skinsbursky@...allels.com>  writes:
>>
>>> 19.12.2011 20:37, Eric W. Biederman пишет:
>>>> Stanislav Kinsbursky<skinsbursky@...allels.com>   writes:
>>>>
>>>> Doing that independently of the rest of the sysctls is pretty horrible
>>>> and confusing to users.   What I am planning might suit your needs and
>>>> if not we need to talk some more about how to get the vfs to do
>>>> something reasonable.
>>>>
>>>
>>> Ok, Eric. Would be glad to discuss your sysctls plans.
>>> But actually you already know my needs: I would like to make sysctls work in the
>>> way like sysfs does: i.e. content of files depends on mount maker -
>>> not viewer.
>>
>> What drives the desire to have sysctls depend on the mount maker?
>
> Because we can (will, actually) have nested fs root's for containers. IOW,
> container's root will be accessible from it's creator context. And I want to
> tune container's fs from creators context.

Tuning the child context from the parent context is an entirely
reasonable thing to do.  To affect a namespace that is not yours
the requirement is simply that we don't use current to lookup the
sysctl.  So what I am proposing should work for your case.

>> Especially what drives that desire not to have it have a /proc/<pid>/sys
>> directory that reflects the sysctls for a given process.
>>
>
> This is not so important for me, where to access sysctl's. But I'm worrying
> about backward compatibility. IOW, I'm afraid of changing path
> "/proc/sys/sunprc/*" to "/proc/<pid>/sys/sunrpc". This would break a lot of
> user-space programs.

The part that keeps it all working is by adding a symlink from /proc/sys
to /proc/self/sys.  That technique has worked well for /proc/net, and I
don't expect there will be any problems with /proc/sys either.  It is
possible but is very rare for the introduction of a symlink in a path
to cause problems.

Eric

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