linux-kernel - Re: [RFC 0/5] livepatch: new API to track system state changes

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Date:   Fri, 21 Jun 2019 09:19:32 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/5] livepatch: new API to track system state changes

On Tue, Jun 11, 2019 at 03:56:22PM +0200, Petr Mladek wrote:
> Hi,
> 
> this is another piece in the puzzle that helps to maintain more
> livepatches.
> 
> Especially pre/post (un)patch callbacks might change a system state.
> Any newly installed livepatch has to somehow deal with system state
> modifications done be already installed livepatches.
> 
> This patchset provides, hopefully, a simple and generic API that
> helps to keep and pass information between the livepatches.
> It is also usable to prevent loading incompatible livepatches.
>

Thanks for posting, Petr and aplogies for not getting to this RFC
earlier.  I think this strikes a reasonable balance between the (too) 
"simplified" versioning scheme that I posted a few weeks back, and what
I was afraid might have been too complicated callback-state-version
concept.

This RFC reads fairly straightforward and especially easy to review
given the included documentation and self-tests.  I'll add a few
comments per patch, but again, I like how this came out.

> There was also a related idea to add a sticky flag. It should be
> easy to add it later. It would perfectly fit into the new struct
> klp_state.

I think so, too.  It would indicate that the patch is introducing a
state which cannot be safely unloaded.  But we can talk about that at a
later time if/when we want to add that wrinkle to klp_state.

-- Joe