linux-kernel - Re: A udev rule to serve the change event of ACPI container?

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Date:   Mon, 24 Jul 2017 17:29:21 +0800
From:   joeyli <jlee@...e.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: A udev rule to serve the change event of ACPI container?

On Mon, Jul 24, 2017 at 10:57:02AM +0200, Michal Hocko wrote:
> On Wed 19-07-17 17:09:10, Joey Lee wrote:
> > On Mon, Jul 17, 2017 at 11:05:25AM +0200, Michal Hocko wrote:
> [...]
> > > The problem I have with this expectation is that userspace will never
> > > have a good atomic view of the whole container. So it can only try to
> > 
> > I agreed!
> > 
> > Even a userspace application can handle part of offline jobs. It's
> > still possible that other kernel/userland compenents are using the
> > resource in container.
> > 
> > > eject and then hope that nobody has onlined part of the container.
> > > If you emit offline event to the userspace the cleanup can be done and
> > > after the last component goes offline then the eject can be done
> > > atomically.
> > 
> > The thing that we didn't align is how does kernel maintains the flag
> > of ejection state on container.
> 
> Why it cannot be an attribute of the container? The flag would be set
> when the eject operation is requested and cleared when either the
> operation is successful (all parts offline and eject operation acked
> by the BIOS) or it is terminated.
>

For the success case, yes, we can clear the flag when the _EJ0 of container
is success. But for the fail case, we don't know when the operation is
terminated.
 
> [...]
> > Base on the above figure, if userspace didn't do anything or it
> > just performs part of offline jobs. Then the container's [eject]
> > state will be always _SET_ there, and kernel will always check
> > the the latest child offline state when any child be offlined
> > by userspace.
> 
> What is a problem about that? The eject is simply in progress until all
> is set. Or maybe I just misunderstood.
>

I agree, but it's only for success case. For fail case, kernel can not
wait forever. Can we?
 
> > 
> > On the other hand, for retry BIOS, we will apply the same
> > _eject_ flag approach on retry BIOS. If the OS performs
> > offline/ejection jobs too long then the retry BIOS is finally
> > time out. There doesn't have way for OS to aware the timeout.
> 
> Doesn't BIOS notify the OS that the eject has timed out?
> 

No, there doesn't have interface to notify OS for BIOS time out. 

Thanks a lot!
Joey Lee