On Mon, Nov 17, 2008 at 09:09, Yu Zhao [off-list ref] wrote:

On Fri, Nov 14, 2008 at 08:55:38AM +0800, Greg KH wrote:

quoted

There are also "conditional" attributes, which get only displayed if
some kind of condition is met, I think you want to use those.

The problem is the sysfs directory of the PCI device is created by the
kobject_add() in the device_add() as follows. And the static entries
bundled with the 'pci_bus_type' are created by the bus_add_device().
Between the kobject_add() and the kobject_uevent(), we don't have any
other choice to add the dynamic entries.

In device_add():

       error = kobject_add(&dev->kobj, dev->kobj.parent, "%s", dev->bus_id);
       ...
       error = bus_add_device(dev);
       ...
       kobject_uevent(&dev->kobj, KOBJ_ADD);


So looks like the only way is to make the dynamic entries bundled with
the 'pci_bus_type', which means they would become static no matter the
device supports the entries (i.e. corresponding capabilities) or not.

There is device_add_attrs() which is just called between the calls you
mention above. Like Greg said, it can add groups, and groups have an
is_visible() callback, which can be used to conditionally create
attributes out of of predefined list.

Kay