linux-kernel - Re: [PATCH 0/2] ACPI / hotplug / driver core: Special handling for container devices

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Date:	Sun, 29 Dec 2013 15:20:47 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	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>
Subject: Re: [PATCH 0/2] ACPI / hotplug / driver core: Special handling for container devices

On Saturday, December 28, 2013 07:59:09 PM Greg Kroah-Hartman wrote:
> On Fri, Dec 27, 2013 at 11:21:59PM +0100, Rafael J. Wysocki wrote:
> > Hi Greg,
> > 
> > The following series of 2 patches (patch [2/2] in particular) make changes
> > needed to handle hot-removal of system container devices (represented by
> > ACPI container and module device objects) on Fujitsu systems.  Those devices
> > represent things like CPU packages, so we need to be able to take care of them
> > cleanly for things like in-the-field CPU socked replacement to work.
> > 
> > The problem being addressed here is that on the systems in question the removal
> > of container devices has to be carried out with the help of user space that
> > needs to be notified of the container removal before the kernel attempts to
> > offline any devices below the container (e.g. in the package represented by the
> > container device object in the ACPI tables).  However, our current code works
> > the other way around and the entire thing is messed up.
> > 
> > This patchset adds the bare bones of what's needed to address that issue and it
> > should be possible to build on top of the code added by it in the future if
> > need be.
> > 
> > Patch [1/2] introduces a new demand_offline flag for struct acpi_hotplug_profile
> > that makes acpi_scan_hot_remove() check the offline status of the device object's
> > companion physical devices to start with and return -EBUSY if at least one of them
> > is not offline.
> > 
> > Patch [2/2] uses that flag to implement the container handling.  The details are
> > in the changelog, but that's how it works.
> > 
> > During the initial namespace scan the container ACPI scan handler creates
> > "physical" system container device under /sys/devices/system/container/ for
> > each ACPI container object whose status is "present" at that time (the sysfs
> > name of that device is the same as the sysfs name of the corresponding
> > container object and they are linked to each other via the firmware_node and
> > physical_node symbolic links, respectively).  Those system container devices
> > are initially online.
> > 
> > The container ACPI scan handler has the demand_offline flag set in its hotplug
> > profile, so when a container eject event happens, acpi_scan_hot_remove() will
> > notice that the flag is set in the device object's scan handler and will
> > check the online status of its "physical" companion device, which is online
> > (that is the system container device the above paragraph is about).  That will
> > cause KOBJ_CHANGE to be emitted for the system container device and -EBUSY to
> > be returned by acpi_scan_hot_remove().  User space is expected to respond to
> > that KOBJ_CHANGE by doing what's necessary to remove the container.
> > 
> > To that end, it needs to offline the system container device through its online
> > sysfs attribute (which is present, because the bus type for containers provides
> > the online and offline callbacks).  However, the offline for system container
> > devices will only succeed if the physical devices right below the container
> > (e.g. in the package represented by it) are all offline, so user space will
> > have to offline those devices before attempting to offline the system container
> > device itself.  When finished, user space can trigger the container removal
> > with the help of the eject sysfs attribute of the ACPI container object pointed
> > to by the system container device's firmware_node link (this time the check in
> > acpi_scan_hot_remove() will succeed, because the system container device in
> > question is now offline).
> > 
> > Please let me know if you have any objections.  If not, I'd like to queue up
> > these patches for 3.14.
> 
> No objection from me, I've acked the second patch, feel free to take
> both of them in your tree.

I will, thanks a lot!

Rafael

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