[QUESTION/sysfs] strange refcounting

["Artem B. Bityutskiy" <dedekind@oktetlabs.ru>]

Hello folks,

I'm writing a simple device driver and want to expose some of its 
attributes to userspace via sysfs.

As usually, I have main device description structure "struct 
mydev_info". I've embedded a struct device object there. What I do is:

struct mydev_info mydev
{
	struct device *dev;
	... bla bla bla ...
} mydev;


mydev->dev=kzalloc(sizeof(struct device), GFP_KERNEL);
mydev->dev->bus_id = "mydev";
mydev->dev->release = mydev_release;
err = device_register(&mydev->dev);

Then, I see /sys/devices/mydev/ in sysfs. I open pre-defined 
/sys/devices/mydev/power/state in userspace and don't close it.

Then I run lsmod, and see zero refcount to my module. Well, I run rmmod 
mymod, module is unloaded.

Then I close /sys/devices/mydev/power/state, and enjoy segfault.

I thought sysfs subsystem have to increase module refcount when one 
opens its sysfs files. Well, there is a release function, but it is also 
unloaded with the module.

May be there is a problem because of I have mydev->dev->parent == NULL, 
mydev->dev->bus == NULL, mydev->dev->driver == NULL? But I really don't 
have any bus, any parent and I don't want to introduce struct 
device_driver ...

Kernel is 2.6.15.1.

Although this is my first meet with sysfs, this looks strange.

Thanks.

-- 
Best regards, Artem B. Bityutskiy
Oktet Labs (St. Petersburg), Software Engineer.
+78124286709 (office) +79112449030 (mobile)
E-mail: dedekind@oktetlabs.ru, web: http://www.oktetlabs.ru