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

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Message-ID: <20170626085907.GE11534@dhcp22.suse.cz>
Date:   Mon, 26 Jun 2017 10:59:07 +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 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.
-- 
Michal Hocko
SUSE Labs