Subject: [QUESTION/sysfs] strange refcounting
From: "Artem B. Bityutskiy" <dedekind@infradead.org>
Reply-To: dedekind@infradead.org
To: linux-kernel@vger.kernel.org
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Organization: MTD
Date: Sat, 04 Feb 2006 11:13:41 +0300
Message-Id: <1139040821.13125.4.camel@sauron.oktetlabs.ru>
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Sender: linux-kernel-owner@vger.kernel.org
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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. Bityuckiy,
St.-Petersburg, Russia.

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