Re: [PATCH v5 02/22] liveupdate: luo_core: integrate with KHO

[Pasha Tatashin <pasha.tatashin@soleen.com>]

Hi Mike,

Thank you for review, my comments below:

> > This is why this call is placed first in reboot(), before any
> > irreversible reboot notifiers or shutdown callbacks are performed. If
> > an allocation problem occurs in KHO, the error is simply reported back
> > to userspace, and the live update update is safely aborted.
>
> This is fine. But what I don't like is that we can't use kho without
> liveupdate. We are making debugfs optional, we have a way to call

Yes you can: you can disable liveupdate (i.e. not supply liveupdate=1
via kernel parameter) and use KHO the old way: drive it from the
userspace. However, if liveupdate is enabled, liveupdate becomes the
driver of KHO as unfortunately KHO has these weird states at the
moment.

> kho_finalize() on the reboot path and it does not seem an issue to do it
> even without liveupdate. But then we force kho_finalize() into
> liveupdate_reboot() allowing weird configurations where kho is there but
> it's unusable.

What do you mean KHO is there but unusable, we should not have such a state...

> What I'd like to see is that we can finalize KHO on kexec reboot path even
> when liveupdate is not compiled and until then the patch that makes KHO
> debugfs optional should not go further IMO.
>
> Another thing I didn't check in this series yet is how finalization driven
> from debugfs interacts with liveupdate internal handling?

I think what we can do is the following:
- Remove "Kconfig: make debugfs optional" from this series, and
instead make that change as part of stateless KHO work.
- This will ensure that when liveupdate=0 always KHO finalize is fully
support the old way.
- When liveupdate=1 always disable KHO debugfs "finalize" API, and
allow liveupdate to drive it automatically. It would add another
liveupdate_enable() check to KHO, and is going to be removed as part
of stateless KHO work.

Pasha