RE: [PATCH 2/3] hv_utils: Support host-initiated hibernation request

[Dexuan Cui]

> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Sent: Thursday, September 12, 2019 9:27 AM
> 
> Dexuan Cui <decui@xxxxxxxxxxxxx> writes:
> 
> > +static void perform_hibernation(struct work_struct *dummy)
> > +{
> > +	/*
> > +	 * The user is expected to create the program, which can be a simple
> > +	 * script containing two lines:
> > +	 * #!/bin/bash
> > +	 * echo disk > /sys/power/state
> 
> 'systemctl hibernate' is what people do nowadays :-)

Thanks for sharing this command! 
 
> > +	 */
> > +	static char hibernate_cmd[PATH_MAX] = "/sbin/hyperv-hibernate";
> > +
> 
> Let's not do that (I remember when we were triggering network restart
> from netvsc and it was a lot of pain).
> 
> Receiving hybernation request from the host is similar to pushing power
> button on your desktop: an ACPI event is going to be generated and your
> userspace will somehow react to it. I see two options:
> 1) We try to hook up some existing userspace (udev?)
> 2) We write a new hyperv-daemon handling the request (with a config file
> instead of hardcoding please).
> 
> Vitaly

Thanks for the suggestions! 
I prefer the udev method, e.g. something like this:

	char *uevent_env[2] = { "EVENT=hibernate", NULL };
	kobject_uevent_env(&ctx->dev->device.kobj, KOBJ_CHANGE, uevent_env);

Then the user is expected to create the below udev rule file, which is applied
upon the host-initiated hibernation request:

root@localhost:~# cat /usr/lib/udev/rules.d/40-vm-hibernation.rules
SUBSYSTEM=="vmbus", ACTION=="change", DRIVER=="hv_utils", ENV{EVENT}=="hibernate", RUN+="/usr/bin/systemctl hibernate"

The full patch is here:
https://github.com/dcui/linux/commit/0d92b53f48a8dca92bbd3493ea9c5bd098c99623

I'll post it as v2.

Thanks,
-- Dexuan