Re: [PATCH 4/4] ACPI / PM: Expose lists of device power resources to user space

Rafael J. Wysocki
2013-01-23T00:02:56Z

On Tuesday, January 22, 2013 03:56:24 PM Greg Kroah-Hartman wrote:
> On Tue, Jan 22, 2013 at 03:28:23AM +0100, Rafael J. Wysocki wrote:
> > +static struct attribute *attrs[] = {
> > + NULL,
> > +};
>
> That's "odd"...

Well, I don't really need file attributes here (at least at the moment),
but sysfs_create_group() will complain if I just pass NULL in there.

> > +static void acpi_power_hide_list(struct acpi_device *adev,
> > + struct acpi_device_power_state *ps,
> > + const char *group_name)
> > {
> > - if (adev->power.flags.power_resources) {
> > - struct acpi_device_power_state *ps;
> > - struct acpi_power_resource_entry *entry;
> > -
> > - ps = &adev->power.states[ACPI_STATE_D0];
> > - list_for_each_entry(entry, &ps->resources, node) {
> > - struct acpi_power_resource *resource = entry->resource;
> > -
> > - if (add)
> > - acpi_power_add_dependent(resource, adev);
> > - else
> > - acpi_power_remove_dependent(resource, adev);
> > + struct attribute_group attr_group = {
> > + .name = group_name,
> > + .attrs = attrs,
> > + };
>
> This is on the stack, which seems like it would not be good...
>
> > + struct acpi_power_resource_entry *entry;
> > +
> > + list_for_each_entry_reverse(entry, &ps->resources, node) {
> > + struct acpi_device *res_dev = &entry->resource->device;
> > +
> > + sysfs_remove_link_from_group(&adev->dev.kobj, group_name,
> > + dev_name(&res_dev->dev));
> > + }
> > + sysfs_remove_group(&adev->dev.kobj, &attr_group);
>
> You aren't removing the same group that you created. Well, kind of, but
> that's strange, it really works?

Yes, it does, as far as I can say.

> > +static void acpi_power_expose_list(struct acpi_device *adev,
> > + struct acpi_device_power_state *ps,
> > + const char *group_name)
> > +{
> > + struct attribute_group attr_group = {
> > + .name = group_name,
> > + .attrs = attrs,
> > + };
>
> again a structure on the stack.
>
> Why not just create the attribute groups as static, instead of
> "pseudo-dynamically" like you are doing here?

Basically because I'm lazy. :-)

They can be static if that's better.

> I have no idea if sysfs
> can properly cope with an attribute group pointer that disappears after
> it has been registered with the sysfs core. That seems ripe for
> problems, don't you agree?

I don't think so having looked at the code, but I very well might overlook
something. I'll change that.

> Oh, and same question about racing userspace, you will have problems
> here in that the symlinks will be showing up after the device is
> created. Perhaps, to make the whole thing easier, you just change the
> acpi core code to hold off on the notification until you get all of
> these links and files set up and then tell userspace. That's probably
> an easier fix.

I suppose so.

How can I do that?

Rafael

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