* [QUESTION/sysfs] strange refcounting
@ 2006-02-03 14:16 Artem B. Bityutskiy
2006-02-03 17:08 ` Greg KH
0 siblings, 1 reply; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-03 14:16 UTC (permalink / raw)
To: linux-kernel; +Cc: greg
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
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [QUESTION/sysfs] strange refcounting
2006-02-03 14:16 [QUESTION/sysfs] strange refcounting Artem B. Bityutskiy
@ 2006-02-03 17:08 ` Greg KH
0 siblings, 0 replies; 7+ messages in thread
From: Greg KH @ 2006-02-03 17:08 UTC (permalink / raw)
To: Artem B. Bityutskiy; +Cc: linux-kernel
On Fri, Feb 03, 2006 at 05:16:22PM +0300, Artem B. Bityutskiy wrote:
> 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;
First off, this should not be a pointer, but rather:
struct device dev;
That properly embedds the struct device into your object.
> ... 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);
What type of bus does this device live on? You should not be calling
device_register() on your own directly. Either use a bus, and be a
device of it, or use the platform_device() interface.
> 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.
Yup.
> Then I close /sys/devices/mydev/power/state, and enjoy segfault.
What is the backtrace?
> 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.
Again, register with a bus or use the platform_device() interface, and
this should work properly.
> 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 ...
Yes, you kind of need all of that :)
Make the above changes and let us know if that helps things.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [QUESTION/sysfs] strange refcounting
2006-02-06 9:58 ` Artem B. Bityutskiy
@ 2006-02-06 17:20 ` Artem B. Bityutskiy
0 siblings, 0 replies; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-06 17:20 UTC (permalink / raw)
To: Artem B. Bityutskiy; +Cc: linux-kernel
Artem B. Bityutskiy wrote:
> In connection with this, I have a question. There is a whole bunch of
> drivers which do not directly relate to hardware devices, but which
> still want to expose their parameters via sysfs. For example, this could
> be a filesystem, LVM, a compression layer on top of a file system of a
> block device, whatever. These are "virtual" devices and they are not
> physically connected to any bus. How should they deal with sysfs?
For some reasons I missed Greg's reply to my first message and was
talking to myself. To end this thread, the answer to this question is:
"include/sysfs.h".
--
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [QUESTION/sysfs] strange refcounting
2006-02-04 13:33 ` Artem B. Bityutskiy
@ 2006-02-06 9:58 ` Artem B. Bityutskiy
2006-02-06 17:20 ` Artem B. Bityutskiy
0 siblings, 1 reply; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-06 9:58 UTC (permalink / raw)
To: linux-kernel
As &struct device structure has no @owner field, and corresponding
functions rely on the @owner field at &struct device_driver, I conclude
that I cannot use &struct device objects without bus and device driver
objects, just by design.
On the other hand, 'device_register()' accepts &struct device objects
with NULL-filled @bus and @driver fields perfectly fine, does not
complain, does not return any error, and I even see corresponding
entries at /sys/devices/. But there is a refcounting problem described
at my first mail.
This is obviously a confusing discrepancy. Sysfs has to either reject
bus-less and driver-less &struct device objects or deal with them
correctly. The latter is impossible due to lack of an @owner field in
&struct device.
In connection with this, I have a question. There is a whole bunch of
drivers which do not directly relate to hardware devices, but which
still want to expose their parameters via sysfs. For example, this could
be a filesystem, LVM, a compression layer on top of a file system of a
block device, whatever. These are "virtual" devices and they are not
physically connected to any bus. How should they deal with sysfs?
I see there is the "class" stuff in sysfs, but it seems that it is far
not as flexible as the "device, driver, and bus" stuff, because I cannot
create many nested layers within classes. I can create a class, which
goes to /sys/class/, and devices within this class, which go to
/sys/class/myclass/mydev/. But I cannot create a class, devices within
that class, and daughter devices within them, like:
/sys/class/myclass/
|-- mydev1/
| -- doughterdev1/
| -- doughterdev1/
| -- ...
|-- mydev2/
|-- mydev3/
|-- ...
Please, comment this.
Thanks.
--
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [QUESTION/sysfs] strange refcounting
2006-02-04 12:04 ` Artem B. Bityutskiy
@ 2006-02-04 13:33 ` Artem B. Bityutskiy
2006-02-06 9:58 ` Artem B. Bityutskiy
0 siblings, 1 reply; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-04 13:33 UTC (permalink / raw)
To: linux-kernel
Artem B. Bityutskiy wrote:
> I actually forgot to formulate my question: why module's refcount is not
> increased when somebody opens a sysfs file which belongs to this module?
> How to withstan to an unexpected module unload?
>
> Thanks.
I see this code drivers/base/core.c, device_add().
if (dev->driver)
dev->uevent_attr.attr.owner = dev->driver->owner;
I assume it is expected that I must have a driver structure. But I
don't. Why do I have to?
--
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [QUESTION/sysfs] strange refcounting
2006-02-04 8:13 Artem B. Bityutskiy
@ 2006-02-04 12:04 ` Artem B. Bityutskiy
2006-02-04 13:33 ` Artem B. Bityutskiy
0 siblings, 1 reply; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-04 12:04 UTC (permalink / raw)
To: linux-kernel
Artem B. Bityutskiy wrote:
> 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 actually forgot to formulate my question: why module's refcount is not
increased when somebody opens a sysfs file which belongs to this module?
How to withstan to an unexpected module unload?
Thanks.
--
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [QUESTION/sysfs] strange refcounting
@ 2006-02-04 8:13 Artem B. Bityutskiy
2006-02-04 12:04 ` Artem B. Bityutskiy
0 siblings, 1 reply; 7+ messages in thread
From: Artem B. Bityutskiy @ 2006-02-04 8:13 UTC (permalink / raw)
To: linux-kernel
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.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2006-02-06 17:20 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2006-02-03 14:16 [QUESTION/sysfs] strange refcounting Artem B. Bityutskiy
2006-02-03 17:08 ` Greg KH
2006-02-04 8:13 Artem B. Bityutskiy
2006-02-04 12:04 ` Artem B. Bityutskiy
2006-02-04 13:33 ` Artem B. Bityutskiy
2006-02-06 9:58 ` Artem B. Bityutskiy
2006-02-06 17:20 ` Artem B. Bityutskiy
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