[RFC PATCH 2.6.12-rc2-mm2 0/2] i2c: new sysfs class "hwmon"

Greg KH greg at kroah.com
Tue Apr 12 23:55:55 CEST 2005

On Mon, Apr 11, 2005 at 12:44:27AM -0400, Mark M. Hoffman wrote:
> Hi Khali, Greg, et. al:
> After a brief chat w/ Khali last week (and some reading LDDv3) I did these
> patches.  The result for me looks like this:
> /sys/class/hwmon/1-0290/device/ -> /sys/devices/platform/i2c-1/1-0290
> Notes/Questions:

First a question from me, why?  What are you trying to do here?  Who
will be using the hwmon class?  And what for?  Will all "sensor-like"
sysfs files move to this new class, or is it just to enable userspace to
be able to find the hwmon devices easier?

> 1. I don't like "1-0290" for a class ID, but it was the easiest thing to
> use at the time.  A better name might be w83627thf-0.

As long as it's unique, that's the only requirement.

> 2. The kernel complains if I don't provide a class::release function, but
> I can't really see a need for it in this case.  If I hold a file open through
> the /sys/class/hwmon/X/device/Y link and then try to rmmod the driver, the 
> rmmod will sleep until I close the file just as I expect.  Any hints here
> Greg?

Ick, yes, you _must_ have a release function.  _Please_ listen to the
kernel, it isn't saying those things for no reason...  If you add a file
to the class device, and do not have a release function, then you can
have a memory leak.  The way that you use the class device owned by a
different device is not safe, nor a good idea.  I recommend using the
"class_device_create()" function that has been added to the -mm tree (or
the class_simple stuff that's in mainline, if you want an idea of what
it is.  Hm, no that will not quite work, that's why I wrote the
class_device_create() call...use that.)

> 3. I added the struct class_device to struct i2c_client.  This makes it
> slightly easier to modify the sensors drivers... but not all i2c_clients
> will need it (bloat).  It could be added to each struct <driver>_data
> (e.g. w83627hf_data) instead.

Use a pointer instead, and the class_device_create function.


greg k-h

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