How to correctly setup a sysfs class

How to correctly setup a sysfs class

[Kylene Hall]

Hello-

I am trying to create a class in the sysfs filesystem for the tpm device
driver to use. It was brought to my attention that my first attempts
were missing a release function and thus causing ugly messages in
/var/log/messages.  The problem I have is I do not know what I need to
put in the release function.  The class_simple was recommended to me put
I don't think it meets my needs.

What I'd like to do is that when an application is built on top of this
driver and needs to know where to find the sysfs files for the device,
it doesn't have to look on all the different buses in /sys.  Today TPMs 
are pci devices but in the future they could be usb devices as well.  By
createing the tpm class and adding each device to the class the device
link that is created can be followed to find the necessary files.  When
using class_simple it seems the only file that can be created in the
class is dev which contains the major and minor number.  There is no
link to the actual device created and since you don't have access to the
actual struct class you can't create the link either.  Please direct me
if there is another way to do this.

Thanks,
Kylie Hall



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Re: How to correctly setup a sysfs class

[Greg KH]

On Tue, Feb 08, 2005 at 03:05:59PM -0600, Kylene Hall wrote:
> Hello-
> 
> I am trying to create a class in the sysfs filesystem for the tpm device
> driver to use. It was brought to my attention that my first attempts
> were missing a release function and thus causing ugly messages in
> /var/log/messages.  The problem I have is I do not know what I need to
> put in the release function.  The class_simple was recommended to me put
> I don't think it meets my needs.

I think linux-kernel is the best place for this...  But anyway...

> What I'd like to do is that when an application is built on top of this
> driver and needs to know where to find the sysfs files for the device,
> it doesn't have to look on all the different buses in /sys.

But you are using the misc device interface, right?  Why not just use
that class interface?  You have a pointer to the class_device offered to
you in the misc structure that is for you to put sysfs files into the
tree.  Just make sure to clean them up when you are done.

> Today TPMs are pci devices but in the future they could be usb devices
> as well.

Ok, you could hang your files off of the struct device if you want too.
All depends on what you feel comfortable with.

> By createing the tpm class and adding each device to the class the
> device link that is created can be followed to find the necessary
> files.  When using class_simple it seems the only file that can be
> created in the class is dev which contains the major and minor number.

No, you have a pointer to the class device that you can then pass to the
"create a class device file" function, right?  That's why you are passed
back a pointer.

> There is no link to the actual device created and since you don't have
> access to the actual struct class you can't create the link either.
> Please direct me if there is another way to do this.

See above.

thanks,

greg k-h


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