Re: [Update 4][PATCH 2/7] ACPI / scan: Introduce common code for ACPI-based device hotplug

[Rafael J. Wysocki]

On Monday, February 25, 2013 11:07:52 AM Toshi Kani wrote:
> On Sat, 2013-02-23 at 22:38 +0000, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > 
> > Multiple drivers handling hotplug-capable ACPI device nodes install
> > notify handlers covering the same types of events in a very similar
> > way.  Moreover, those handlers are installed in separate namespace
> > walks, although that really should be done during namespace scans
> > carried out by acpi_bus_scan().  This leads to substantial code
> > duplication, unnecessary overhead and behavior that is hard to
> > follow.
> > 
> > For this reason, introduce common code in drivers/acpi/scan.c for
> > handling hotplug-related notification and carrying out device
> > insertion and eject operations in a generic fashion, such that it
> > may be used by all of the relevant drivers in the future.  To cover
> > the existing differences between those drivers introduce struct
> > acpi_hotplug_profile for representing collections of hotplug
> > settings associated with different ACPI scan handlers that can be
> > used by the drivers to make the common code reflect their current
> > behavior.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> > 
> > This update causes acpi_bus_device_eject() to only emit KOBJ_OFFLINE uevent if
> > autoexec is unset for the given scan handler.
> > 
> > This will require the doc in patch [5/7] to be updated which I'm going to do if
> > everyone is OK with the $subject patch.
> > 
> > Thanks,
> > Rafael
>  :
> > +
> > +static void acpi_scan_bus_device_check(acpi_handle handle, u32 ost_source)
> > +{
> > +	struct acpi_device *device = NULL;
> > +	u32 ost_code = ACPI_OST_SC_NON_SPECIFIC_FAILURE;
> > +	int error;
> > +
> > +	mutex_lock(&acpi_scan_lock);
> > +
> > +	acpi_bus_get_device(handle, &device);
> > +	if (device) {
> > +		dev_warn(&device->dev, "Attempt to re-insert\n");
> > +		goto out;
> > +	}
> > +	acpi_evaluate_hotplug_ost(handle, ost_source,
> > +				  ACPI_OST_SC_INSERT_IN_PROGRESS, NULL);
> > +	error = acpi_bus_scan(handle);
> > +	if (error) {
> > +		acpi_handle_warn(handle, "Namespace scan failure\n");
> > +		goto out;
> > +	}
> > +	error = acpi_bus_get_device(handle, &device);
> > +	if (error) {
> > +		acpi_handle_warn(handle, "Missing device node object\n");
> > +		goto out;
> > +	}
> > +	ost_code = ACPI_OST_SC_SUCCESS;
> > +	if (device->handler && device->handler->hotplug.uevents)
> > +		kobject_uevent(&device->dev.kobj, KOBJ_ONLINE);
> 
> I confirmed that the uevent crash issue was solved.  Thinking further, I
> wonder if we need to emit KOBJ_ONLINE here.  This behavior is asymmetric
> since we do not emit KOBJ_OFFLINE when autoeject is set.

Well, I put that in there only to be able to make the container driver behave
in a backwards compatible way (which is to emit KOBJ_ONLINE at this point).

If the container driver doesn't need to emit KOBJ_ONLINE at all, I agree with
your suggestion.

> The definition of ONLINE/OFFLINE event to an ACPI device object seems also
> bogus since there is no online/offline operation to the ACPI device object
> itself.
> Online/offline operation is only possible to actual device, such as
> system/cpu/cpu% and system/memory/memory%.

That's correct, but I don't know what the user space expectations are
currently.

> So, I'd suggest the following changes.
>  - Remove the "uevents" attribute.  KOBJ_ONLINE/OFFLINE are not used for
> ACPI device objects.
>  - Make the !autoeject case as an exception for now, and emit
> KOBJ_OFFLINE as a way to request off-lining to user.  This uevent is
> tied with the !autoeject case.  We can then revisit if this use-case
> needs to be supported going forward.  If so, we may want to consider a
> different event type.

Well, what about avoiding to expose uevents and autoeject for now and
exposing enabled only?  Drivers would still be able to set the other flags on
init on init to enforce the backwards-compatible behavior.

I agree that it would be sufficient to use one additional flag then, to start
with, but its meaning would be something like "keep backwards compatibility
with the old container driver", so perhaps "autoeject" is not a good name.

What about "user_eject" (that won't be exposed to user space) instead?  Where,
if set, it would meand "do not autoeject and emit KOBJ_OFFLINE/ONLINE uevents
like the old container driver did"?

Rafael


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