linux-kernel - Re: [PATCH v2] reboot: allow to specify reboot mode via sysfs

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Message-ID: <CAFnufp2_3Ghyhs-kEBepdsGZ6c+x66z=T7m4Uyc1Xi48TwK8jw@mail.gmail.com>
Date:   Sat, 7 Nov 2020 00:19:05 +0100
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Arnd Bergmann <arnd@...db.de>, Petr Mladek <pmladek@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Kees Cook <keescook@...omium.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>
Subject: Re: [PATCH v2] reboot: allow to specify reboot mode via sysfs

On Fri, Nov 6, 2020 at 11:33 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri,  6 Nov 2020 21:07:04 +0100 Matteo Croce <mcroce@...ux.microsoft.com> wrote:
>
> > The kernel cmdline reboot= option offers some sort of control
> > on how the reboot is issued.
> > Add handles in sysfs to allow setting these reboot options, so they
> > can be changed when the system is booted, other than at boot time.
>
> Please include a description of why you believe the kernel needs this
> feature.  Use cases, end-user benefits, etc.
>
> We've survived this long without it - what changed?

Hi Andrew,

We don't always know in advance what type of reboot to perform.

Sometimes a warm reboot is preferred to persist certain memory regions
across the reboot. Others a cold one is needed to apply a future system
update that makes a memory memory model change, like changing the base
page size or resizing a persistent memory region.

Or simply we want to enable reboot_force because we noticed that
something bad happened.

Bye,
-- 
per aspera ad upstream