linux-kernel - Re: [PATCH v0 2/3] livepatch: update documentation/samples for callbacks

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Date:   Wed, 28 Feb 2018 14:20:22 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Joe Lawrence <joe.lawrence@...hat.com>
cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Jason Baron <jbaron@...mai.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>
Subject: Re: [PATCH v0 2/3] livepatch: update documentation/samples for
 callbacks

On Tue, 27 Feb 2018, Joe Lawrence wrote:

> On 02/27/2018 07:36 AM, Miroslav Benes wrote:
> > On Fri, 23 Feb 2018, Joe Lawrence wrote:
> > 
> >> [ ... snip ... ]
> >>  
> >> +If a livepatch is replaced by a cumulative patch, then only the
> >> +callbacks belonging to the cumulative patch will be executed.  This
> >> +simplifies the livepatching core for it is the responsibility of the
> >> +cumulative patch to safely revert whatever needs to be reverted.  See
> >> +Documentation/livepatch/cumulative.txt for more information on such
> >> +patches.
> > 
> > s/cumulative/atomic replace/ almost everywhere?
> > 
> > 'Documentation/livepatch/cumulative.txt' should be 
> > 'Documentation/livepatch/cumulative-patches.txt' and we may rename it 
> > atomic-replace-patches.txt. I don't know. Cumulative patches forms a 
> > subset of atomic replace patches in my understanding. The feature itself 
> > is more general. Even if practically used for cumulative patches only. But 
> > it is for you and Petr to decide.
> 
> Hi Miroslav,
> 
> Thanks for reviewing!
> 
> I guess I'm a little confused about the distinction here.
> 
> I understood a "cumulative-patch" to mean that it would contain the sum
> of all changes.  So instead of this:
> 
>   patch 1 = A
> + patch 2 =     B
> + patch 3 =         C
> -----------------------
>   net     = A + B + C
> 
> We can group all of the changes together into a single cumulative-patch
> for the same net effect:
> 
>   patch 1 = A               -replaced by-
>   patch 2 = A + B             -replaced by-
>   patch 3 = A + B + C

Yes.
 
> I assumed this would also mean to include any reverted changes as well.
> So in the example above, if change C needed to be reverted, then:
> 
>   patch 4 = A + B
> 
> and that would still be considered a "cumulative-patch".

Ah, ok. This is where we differ. I didn't consider this to be a cumulative 
patch. But I understand your reasoning. 

Miroslav