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SubjectRe: [PATCH v0 2/3] livepatch: update documentation/samples for callbacks
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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

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".

In my mind, atomic replace is the mechanism that forces patching to be
cumulative. Perhaps this is too strict? Are there other use-cases for
atomic-replace?

>> Example Use-cases
>> =================
>>
>> [ ... snip ... ]
>>
>> +Test 11
>> +-------
>> +
>> +A similar test as the previous one, except this time load the second
>> +callback demo module as a cumulative (ie, replacement) patch. The
>> +livepatching core will only execute klp_object callbacks for the latest
>> +cumulative patch on the patch stack.
>> +
>> +- load livepatch
>> +- load second livepatch (atomic replace)
>> +- disable livepatch
>
> Not needed.

Good catch.

-- Joe

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