Re: [PATCH v2 3/4] livepatch/shadow: Introduce klp_shadow_type structure

Petr Mladek
2022-10-31T16:02:53Z

On Wed 2022-10-26 16:41:21, Marcos Paulo de Souza wrote:
> The shadow variable type will be used in klp_shadow_alloc/get/free
> functions instead of id/ctor/dtor parameters. As a result, all callers
> use the same callbacks consistently[*][**].
>
> The structure will be used in the next patch that will manage the
> lifetime of shadow variables and execute garbage collection automatically.
>
> [*] From the user POV, it might have been easier to pass $id instead
> of pointer to struct klp_shadow_type.
>
> It would require registering the klp_shadow_type so that
> the klp_shadow API could find ctor/dtor for the given id.
> It actually will be needed for the garbage collection anyway
> because it will define the lifetime of the variables.
>
> The bigger problem is that the same klp_shadow_type might be
> used by more livepatch modules. Each livepatch module need
> to duplicate the definition of klp_shadow_type and ctor/dtor
> callbacks. The klp_shadow API would need to choose one registered
> copy.
>
> The definitions should be compatible and they should stay as long
> as the type is registered. But it still feels more safe when
> klp_shadow API callers use struct klp_shadow_type and ctor/dtor
> callbacks defined in the same livepatch module.
>
> This problem is gone when each livepatch explicitly uses its
> own struct klp_shadow_type pointing to its own callbacks.

This paragraph seems redundant. It more or less repeats what
is said in the previous one.

> [**] test_klp_shadow_vars.c uses a custom @dtor to show that it was called.
> The message must be disabled when called via klp_shadow_free_all()
> because the ordering of freed variables is not well defined there.
> It has to be done using another hack after switching to
> klp_shadow_types.
>
> Co-developed-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>

I am never sure how the co-authoring should be done ;-) But I believe
that the author should always be the first one. And the other author
should be listed either by Co-developer-by: or by Signed-off-by: but
not by both tags. So, it should be:

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Co-developed-by: Petr Mladek <pmladek@suse.com>

With the removed paragraph and updated tags:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

PS: No need to resend the patch. I could do the two changes
when pushing it.