Re: [Xen-devel] [PATCH 06/14] livepatch: Add support for apply|revert action replacement hooks

["Wieczorkiewicz, Pawel" <wipawel@amazon.de>]

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On 21. Aug 2019, at 20:31, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com<mailto:konrad.wilk@oracle.com>> wrote:

On 8/21/19 4:19 AM, Pawel Wieczorkiewicz wrote:
By default, in the quiescing zone, a hotpatch payload is applied with
apply_payload() and reverted with revert_payload() functions. Both of
the functions receive the payload struct pointer as a parameter. The
functions are also a place where standard 'load' and 'unload' module
hooks are executed.
To increase hotpatching system's agility and provide more flexiable
long-term hotpatch solution, allow to overwrite the default apply
and revert action functions with hook-like supplied alternatives.
The alternative functions are optional and the default functions are
used by default.
Since the alternative functions have direct access to the hotpatch
payload structure, they can better control context of the 'load' and
'unload' hooks execution as well as exact instructions replacement
workflows. They can be also easily extended to support extra features
in the future.
To simplify the alternative function generation move code responsible
for payload and hotpatch region registration outside of the function.
That way it is guaranteed that the registration step occurs even for
newly supplied functions.

This logic looks legit, but I was wondering if you would be up for a writing a small test-case(s) livepatch that would exercise these parts just to make sure nothing in the future would screw it up?

Yes, I could do that. But, I would like to discuss (get guidelines about) the expected test coverage.
With this sort of changes, there is an unlimited set of test-cases to be created. So, I would like to focus on a few most important.
I am missing knowledge how these test cases are supposed to be used… hence the ask.

Best Regards,
Pawel Wieczorkiewicz



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