[RFC PATCH 2.6.12-rc3] dynamic driver sysfs callbacks and RFC on bmcsensor rewrite

Dmitry Torokhov dmitry.torokhov at gmail.com
Thu Apr 28 16:31:06 CEST 2005

Hi Yani,

On 4/28/05, Yani Ioannou <yani.ioannou at gmail.com> wrote:
> On 4/26/05, Dmitry Torokhov <dtor_core at ameritech.net> wrote:
> > If void is added directly to the attribute structure that means that same
> > attribute can not be shared between several instances of the same device
> > -> unexpected. So far all attributes could be statically created.
> Dmitry: would you mind explaining this a bit more? Also is there
> anywhere else you would suggest adding the callback specific void *
> to? Perhaps creating some new structure(s) to track driver specific
> data for each device?

Mosy of the code does something like that:

static DEVICE_ATTR(blah, 0644, blah_show, blah_store);
and then
         sysfs_create_file(mydev, &blah_device_attr);
or qute often install it as a default driver/bus/device attribute.

In this case one structure is shared between several instances of
driver model objects. With your changes people have to be aware that
they have to allocate attributes dynamically and that they can't use
bus/driver default attribute mechanism nor attribute_groups.

Actually I have toyed with attribute_array and attribute_array_group
for some time. Greg did not like it mostly because there were no
possible users. But it looks like bmcsensort and infiniband could use
attribute arrays, so maybe he'll change his mind. With my patches you
can make initial structure static, all synamic allocations go behind
the scene.



One can use them like this (i8k laptop has 2 fans, this is a legacy SMM driver):

static ssize_t i8k_sysfs_fan_speed_show(struct kobject *kobj, unsigned
int idx, char *buf)
	int speed = i8k_get_fan_speed(idx);
	return speed < 0 ? -EIO : sprintf(buf, "%d\n", speed);

static struct enumerated_attr i8k_fan_attrs[] = {
	__ATTR(state, 0644, i8k_sysfs_fan_show, i8k_sysfs_fan_set),
	__ATTR(speed, 0444, i8k_sysfs_fan_speed_show, NULL),

static struct attribute_group_array i8k_fan_attr_array = {
	.name = "fan",
	.attrs = i8k_fan_attrs,
err = sysfs_create_group_array(&i8k_device->dev.kobj, &i8k_fan_attr_array, num);


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