linux-kernel - Re: [PATCH v6 02/20] liveupdate: luo

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Message-ID: <aRoi-Pb8jnjaZp0X@kernel.org>
Date: Sun, 16 Nov 2025 21:16:08 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v6 02/20] liveupdate: luo_core: integrate with KHO

On Sun, Nov 16, 2025 at 09:55:30AM -0500, Pasha Tatashin wrote:
> On Sun, Nov 16, 2025 at 7:43 AM Mike Rapoport <rppt@...nel.org> wrote:
> >
> > > +static int __init liveupdate_early_init(void)
> > > +{
> > > +     int err;
> > > +
> > > +     err = luo_early_startup();
> > > +     if (err) {
> > > +             pr_err("The incoming tree failed to initialize properly [%pe], disabling live update\n",
> > > +                    ERR_PTR(err));
> >
> > How do we report this to the userspace?
> > I think the decision what to do in this case belongs there. Even if it's
> > down to choosing between plain kexec and full reboot, it's still a policy
> > that should be implemented in userspace.
> 
> I agree that policy belongs in userspace, and that is how we designed
> it. In this specific failure case (ABI mismatch or corrupt FDT), the
> preserved state is unrecoverable by the kernel. We cannot parse the
> incoming data, so we cannot offer it to userspace.
> 
> We report this state by not registering the /dev/liveupdate device.
> When the userspace agent attempts to initialize, it receives ENOENT.
> At that point, the agent exercises its policy:
> 
> - Check dmesg for the specific error and report the failure to the
> fleet control plane.

Hmm, this is not nice. I think we still should register /dev/liveupdate and
let userspace discover this error via /dev/liveupdate ABIs.

> - Trigger a fresh (kexec or cold) reboot to reset unreclaimable resources.
> 
> Pasha
> 

-- 
Sincerely yours,
Mike.