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

[Rafael J. Wysocki]

On Monday, December 23, 2013 02:58:38 PM Rafael J. Wysocki wrote:
> On Saturday, December 14, 2013 06:07:06 AM Rafael J. Wysocki wrote:
> > On Friday, December 13, 2013 02:17:32 PM Yasuaki Ishimatsu wrote:
> > > (2013/12/13 13:56), Rafael J. Wysocki wrote:
> > > > 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.
> > > 
> > > This idea seems to same as your previous work.
> > > http://lkml.org/lkml/2013/2/23/97
> > 
> > No, it is not.  That one didn't involve physical device representations.
> > 
> > > How about add autoremove flag into acpi_hotplug_profile and check it as follow:
> > 
> > This is very similar to "enable" except that it generates the uevent and
> > "enable" doesn't.  You might as well modify "enable" to trigger a uevent if
> > eject is not enabled (note that with the latest patches in linux-next "enable"
> > only applies to eject).
> > 
> > That said I don't think we should generate any uevents for struct acpi_device
> > objects, because they are not devices.
> > 
> > > ---
> > >   drivers/acpi/scan.c | 5 +++++
> > >   1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > > index 5383c81..c43d110 100644
> > > --- a/drivers/acpi/scan.c
> > > +++ b/drivers/acpi/scan.c
> > > @@ -409,6 +409,11 @@ static void acpi_hotplug_notify_cb(acpi_handle handle, u32 type, void *data)
> > >   			ost_code = ACPI_OST_SC_EJECT_NOT_SUPPORTED;
> > >   			goto err_out;
> > >   		}
> > > +		if (!handler->hotplug.autoremove) {
> > > +			kobject_uevent(&device->dev.kobj, KOBJ_CHANGE);
> > > +			ost_code = ACPI_OST_SC_EJECT_NON_SPECIFIC_FAILURE;
> > > +			goto err_out;
> > > +		}
> > >   		acpi_evaluate_hotplug_ost(handle, ACPI_NOTIFY_EJECT_REQUEST,
> > >   					  ACPI_OST_SC_EJECT_IN_PROGRESS, NULL);
> > >   		break;
> > > 
> > > Adding the check into "acpi_hotplug_notify_cb()", user need not change the
> > > flag for removing container device by "sysfs eject".
> > 
> > Which is utterly confusing.  There is no reason whatsoever why the sysfs eject
> > attribute should work differently from the event-triggered eject.  Quite the
> > opposite is the case: it should work in the same way in my opinion so that it
> > is possible to test the eject code path using that attribute.
> > 
> > I'm traveling now, but when I get back home (next week), I'll try to implement
> > the thing I was talking about above.
> 
> It took some more time than I had expected, but I finally was able to get to that.
> 
> The following two patches implement the idea.  This is the minimum (in my opinion)
> implementation and it may be extended in some ways.
> 
> 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 is supposed to work.
> 
> During the initial namespace scan the container ACPI scan handler should create
> "physical" system container device under /sys/devices/system/container/ for
> each ACPI container object (the sysfs name of that device should be the same as
> the sysfs name of the corresponding container object and they should be linked
> to each other via the firmware_node and physical_node symbolic links, respectively).
> Those system container devices are initially online.
> 
> When a container eject event happens, acpi_scan_hot_remove() will notice that
> hotplug.demand_offline 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().
> 
> Now, user space needs to offline the system container device through its online
> sysfs attribute (that should be 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 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).
> 
> The way it is implemented is a bit hackish (the driver_data pointer is slightly
> abused), but that's a special case and I wanted to avoid adding new fields to
> struct device just for handling it.
> 
> The patches haven't been tested yet.  I'm going to do that later today, but
> first I need to take care of some other things, so that has to wait.

The series of the two patches:

[1/2] ACPI / hotplug: Add demand_offline hotplug profile flag
	https://patchwork.kernel.org/patch/3396711/

[2/2] ACPI / hotplug / driver core: Handle containers in a special way
	https://patchwork.kernel.org/patch/3399081/

has been tested now and seems to work as expected, at least for a container
that has no children (that's one I could simulate easily in a meaningful way).

For this reason, if there are no objections, I'll resend them as an official
submission during the next couple of days.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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