How to know the system state if the system is going for halt or poweroff or reboot in FreeBSD

[Sibananda Sahu]

Thanks Lowell Gilbert and John Baldwin for your help.
I have registered an event handler and my job is done easily.

Thanks for your time.

 - Sibananda Sahu


-----Original Message-----
From: Lowell Gilbert [mailto:freebsd-questions-local at be-well.ilk.org]
Sent: Tuesday, April 07, 2015 3:04 AM
To: Sibananda Sahu
Cc: freebsd-questions at freebsd.org
Subject: Re: How to know the system state if the system is going for halt
or poweroff or reboot in FreeBSD

Sibananda Sahu <sibananda.sahu at avagotech.com> writes:

> Hi Lowell Gilbert,
>
> As you said:
> "That's not really a requirement. It's a method you plan to use to
> meet your requirement, but we can only guess at what useful
> functionality you are making these changes to achieve."
>
> Yes that's true.
>
> I am working on mrsas(4) driver on FreeBSD.
> My requirement is to power off the drives (to save power consumption)
> attached to LSI controller if the system is shutting down.
> If the system is rebooting then we need not do anything with the drives'
> power supply.
>
> So to make the above things possible the mrsas(4) driver needs to know
> if the system is really shutting down or it is rebooting.

Okay, that sounds reasonable. I don't know that particular hardware, but I
can find a few things in general.

You are powering down the drives as a way of putting them in a safe state
before control disappears. If the device were capable of shutting itself
down independently of the host computer (and had the power supply to do so
reliably), I assume you would be doing that instead of worrying about the
order in which host components shut down.

If the driver already loads an ACPI table, you may want to go through ACPI
to trigger your power down command. [I don't have any experience writing
code for ACPI either, so I may well be wrong on that point.] Aside from
that, you can register a kernel event handler. I am not sure which event
you would want to hook, but shutdown_final and shutdown_post_sync would be
good candidates.

Sibananda Sahu <sibananda.sahu at avagotech.com> had previously asked:
>> -          Sys_reboot() will call kern_reboot() which in turn end up
calling
>> EVENTHANDLER_INVOKE(shutdown_final, howto);
>>
>> -          Based on the howto variable passed to the kern_reboot()
call,
>> corresponding event handlers will be invoked.

You probably understand this already, but in case you don't:
shutdown_final is an event for which your driver can register.

Good luck.