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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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.

Thanks,
Rafael