linux-kernel - Re: [PATCH 7/10] ACPI / hotplug: Move container-specific code out of the core

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Date:	Fri, 13 Dec 2013 05:56:47 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	"Moore, Robert" <robert.moore@...el.com>,
	Toshi Kani <toshi.kani@...com>,
	Yinghai Lu <yinghai@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Aaron Lu <aaron.lu@...el.com>, Lv Zheng <lv.zheng@...el.com>
Subject: Re: [PATCH 7/10] ACPI / hotplug: Move container-specific code out of the core

On Friday, December 13, 2013 11:56:32 AM Yasuaki Ishimatsu wrote:
> Hi Rafael,

Hi,

> Please share your more detailed idea. I started to implement the following
> idea. But the idea has one problem.
> 
> >>> The eject work flow can be:
> >>>     (1) an eject event occurs,
> >>>     (2) the container "physical" device fails offline in acpi_scan_hot_remove()
> >>>         emmitting, say, KOBJ_CHANGE for the "physical" device,
> >>>     (3) user space notices the KOBJ_CHANGE and does the cleanup as needed,
> >>>     (4) user space changes the "physical" container device flag controlling
> >>>         offline to 0,
> >>>     (5) user space uses the sysfs "eject" attribute of the ACPI container object
> >>>         to finally eject the container,
> >>>     (6) the offline in acpi_scan_hot_remove() is now successful, because the
> >>>         flag controlling it has been set to 0 in step (4),
> >>>     (7) the "physical" container device goes away before executing _EJ0,
> >>>     (8) the container is ejected.
> 
> I want to emit KOBJ_CHANGE before offlining devices on container device at (2).
> But acpi_scan_hot_remove() offlines devices on container device at first.
> So when offline container device, devices on container has been offlined.
> 
> Thus the idea cannot fulfill my necessary feature.

Well, in that case we need to treat containers in a special way at the ACPI
level.  Which is a bit unfortunate so to speak.

To that end I'd try to add a new flag to struct acpi_hotplug_profile, say
.verify_offline, such that if set, it would cause acpi_scan_hot_remove() to
check if all of the "physical" companions of the top-level device are offline
to start with, and if not, it would just emit KOBJ_CHANGE for the companions
that are not offline and bail out.

So the above algorithm would become:

(1) an eject event occurs,
(2) acpi_scan_hot_remove() checks the verify_offline flag in the target device's
    scan_handler structure,
(3) if set (it would always be set for containers), acpi_scan_hot_remove()
    checks the status of the target device's "physical" companions; if at least
    one of them is offline, KOBJ_CHANGE is emitted for that "physical" device,
    and acpi_scan_hot_remove() returns, [I guess we can just emit KOBJ_CHANGE
    for the first companion that is not offline at this point.]
(4) user space notices the KOBJ_CHANGE and does the cleanup as needed; in the
    process it carries out the offline operation for the container's "physical"
    companion (there's only one such companion for each container), [That
    operation for the container itself is trivial, but to succeed it requires
    all devices below the container to be taken offline in advance.]
(5) user space uses the sysfs "eject" attribute of the ACPI container object
    to finally eject the container,
(6) acpi_scan_hot_remove() is now successful, because the container's "physical"
    companion is now offline,
(7) the "physical" container device goes away before executing _EJ0,
(8) the container is ejected.

I think that should work for you.

Thanks,
Rafael

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