Re: [PATCH v4] reboot: allow to specify reboot mode via sysfs

[Matteo Croce]

On Mon, Feb 22, 2021 at 11:03 AM Pavel Machek <pavel@xxxxxx> wrote:
>
> On Tue 2020-11-10 21:27:46, Matteo Croce wrote:
> > From: Matteo Croce <mcroce@xxxxxxxxxxxxx>
> >
> > 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.
>
> We already have a reboot syscall, do we need sysfs interface, too?
>
>
> > +What:                /sys/kernel/reboot/mode
> > +Date:                November 2020
> > +KernelVersion:       5.11
> > +Contact:     Matteo Croce <mcroce@xxxxxxxxxxxxx>
> > +Description: Reboot mode. Valid values are: cold warm hard soft gpio
>
>
> > +What:                /sys/kernel/reboot/type
> > +Date:                November 2020
> > +KernelVersion:       5.11
> > +Contact:     Matteo Croce <mcroce@xxxxxxxxxxxxx>
> > +Description: Reboot type. Valid values are: bios acpi kbd triple efi pci
>
> what is difference between mode and type? What is difference between
> cold and hard for example? WTF is gpio?
>
> > +What:                /sys/kernel/reboot/cpu
> > +Date:                November 2020
> > +KernelVersion:       5.11
> > +Contact:     Matteo Croce <mcroce@xxxxxxxxxxxxx>
> > +Description: CPU number to use to reboot.
>
> Why should user care about this?
>

Mode is the reboot mode (soft, warm, cold, gpio), and type is an x86
specific type, (bios, acpi, uefi, etc.).
I never used GPIO reboot but it's used by some ARM devices.

I didn't invent anything from scratch, I just transposed the settings
available from the kernel command line (see
Documentation/admin-guide/kernel-parameters.txt) to sysfs.
Everithing was already tunable before, like the CPU used during reboot.

-- 
per aspera ad upstream