linux-kernel - Re: [PATCH] livepatch: add sysfs interface /sys/kernel/livepatch/state

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Message-ID: <alpine.LNX.2.00.1506171512290.19134@pobox.suse.cz>
Date:	Wed, 17 Jun 2015 15:20:03 +0200 (CEST)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Li Bin <huawei.libin@...wei.com>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	xiexiuqi@...wei.com
Subject: Re: [PATCH] livepatch: add sysfs interface
 /sys/kernel/livepatch/state

On Wed, 17 Jun 2015, Li Bin wrote:

> On 2015/6/17 16:13, Miroslav Benes wrote:
> > On Wed, 17 Jun 2015, Li Bin wrote:
>
> > The list of applied patches can be obtained just by 'ls 
> > /sys/kernel/livepatch' and their state is in enabled attribute in each 
> > respective patch (no, you cannot obtain the order in the stack).
> 
> But why we cannot obtain it? I think We indeed need the stack order when we
> will disable one patch, at least, we can find out whether it is on the top of
> the stack if failed to disable one patch.

I meant with the current means. It is correct that we do not export 
information about stacking order anywhere.

What we do in kGraft is that there is something like refcount for each 
patch. When the patch is being applied the refcount of all the previous 
patches is increased. Only the patch with the refcount equal to 0 can be 
removed. This information is exported and gives one a clue about the 
order.

So if there is a need to have something like this there would certainly 
be a way (or ways to be precise) how to do it. The question is if we need 
it right now.

Regards,
Miroslav
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