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SubjectRe: [PATCH] livepatch: add (un)patch hooks
On Thu, 13 Jul 2017, Josh Poimboeuf wrote:

> On Wed, Jul 12, 2017 at 10:10:00AM -0400, Joe Lawrence wrote:
> > When the livepatch core executes klp_(un)patch_object, call out to a
> > livepatch-module specified array of callback hooks. These hooks provide
> > a notification mechanism for livepatch modules when klp_objects are
> > (un)patching. This may be most interesting when another kernel module
> > is a klp_object target and the livepatch module needs to execute code
> > after the target is loaded, but before its module_init code is run.
>
> And it's also useful for vmlinux. Patch module load/unload is separate
> from enable/disable, so the module init/exit functions can't be used for
> patch-specific changes (e.g., global data changes).

I admit that I don't understand this, which is probably the reason for my
question. Why do we need it when we have module notifiers and module
init/exit functions in the kernel? Petr described different possible
scenarios and they can be solved either in init/exit function of a patch
module or in a module notifier which the patch module can register.

If there is a difference, it should be mentioned in the documentation and
in the changelog.

> > The patch-hook executes right before patching objects and the
> > unpatch-hook executes right after unpatching objects.
> >
> > Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
>
> Thanks for posting it. We found this to be a useful feature in the
> past, not quite as useful as shadow data, but still good to have for
> certain cases.
>
> Instead of "load hooks" I think it would be more accurate to call them
> "enable/disable hooks". (Maybe "callbacks" would be better than
> "hooks"? Not sure...)
>
> Even better, we might want to be specific: "pre enable hooks" and "post
> disable hooks". (Or "pre patch hooks" and "post unpatch hooks"?)
> Because we might eventually decide we need the corresponding "post
> enable hooks" and "pre disable hooks" as well.

And this is what I'm worried about. I think we don't want to have hooks
sprinkled here and there in the code.

Thanks,
Miroslav

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