+++ Ross Lagerwall [21/09/16 16:47 +0100]:
On 09/20/2016 03:25 PM, Josh Poimboeuf wrote:
On Tue, Sep 20, 2016 at 02:05:36PM +0100, Ross Lagerwall wrote:

The recommended way of applying multiple patches is to apply cumulative
patches on top of the existing ones [1].

If the first patch introduces some new static/global data, the second patch,
being cumulative, will define the same new static/global data. When the
second patch is loaded, it will use its own copy of the new data which may
not contain the same values as the existing data from patch 1.

Has this problem been considered at all? Are there any known solutions?

[1] https://www.redhat.com/archives/kpatch/2015-November/msg00001.html

Hi Ross,

Hm, I don't think we've ever considered this issue.  At least in my
experience, I've never needed to add a global variable which needed to
keep its value across a cumulative update.

Fair enough.

Is this more of a theoretical question, or did you encounter this issue
with a real patch?

It's more of a theoretical question. I was wondering if this would cause issues when patching a machine over a long period of time. But if you think these types of patches wouldn't be needed, then perhaps its not a problem.

Interesting question. I don't think we've ever considered this case
directly, but that's not to say it'd never come up. I would imagine
though that handling such dependencies between old and new patch
modules would quickly become cumbersome...

In this particular scenario though, I think the patch author could
probably use load hooks+kallsyms tricks to, for example, copy the old
values of the static/global variables from the old patch module and
assign to its new static/global variables. Hacky, but it'd probably

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