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

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Message-ID: <20170711082532.GA6927@dhcp22.suse.cz>
Date:   Tue, 11 Jul 2017 10:25:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     joeyli <jlee@...e.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: A udev rule to serve the change event of ACPI container?

On Mon 26-06-17 10:59:07, Michal Hocko wrote:
> On Mon 26-06-17 14:26:57, Joey Lee wrote:
> > Hi all,
> > 
> > If ACPI received ejection request for a ACPI container, kernel
> > emits KOBJ_CHANGE uevent when it found online children devices
> > below the acpi container.
> > 
> > Base on the description of caa73ea15 kernel patch, user space
> > is expected to offline all devices below the container and the
> > container itself. Then, user space can finalize the removal of
> > the container with the help of its ACPI device object's eject
> > attribute in sysfs.
> > 
> > That means that kernel relies on users space to peform the offline
> > and ejection jobs to acpi container and children devices. The
> > discussion is here:
> > 	https://lkml.org/lkml/2013/11/28/520
> > 
> > The mail loop didn't explain why the userspace is responsible for
> > the whole container offlining. Is it possible to do that transparently
> > from the kernel? What's the difference between offlining memory and
> > processors which happends without any cleanup and container which
> > does essentially the same except it happens at once? 
> >  
> >  - After a couple of years, can we let the container hot-remove
> >    process transparently?
> >  - Except udev rule, does there have any other mechanism to trigger
> >    auto offline/ejection?
> 
> I would be also interested whether the kernel can simply send an udev event
> to all devices in the container.

Any opinion on this?
-- 
Michal Hocko
SUSE Labs