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SubjectRe: patch for sysfs in the cyclades driver
On Thu, Nov 04, 2004 at 08:58:21AM -0800, Roland Dreier wrote:
> Marcelo> The problem was class_simple only contains the "dev"
> Marcelo> attribute. You can't add other attributes to it.
> I believe, based on the comment in class_simple.c:
> Any further sysfs files that might be required can be created using this pointer.
> and the implementation in in drivers/scsi/st.c, that there's no
> problem adding attributes to a device in a simple class. You can just
> use class_set_devdata() on your class_device to set whatever context
> you need to get back to your internal structures, and then use
> class_device_create_file() to add the attributes.
> I assume this is OK (since there is already one in-kernel driver doing
> it), but Greg, can you confirm that it's definitely OK for a driver to
> use class_set_devdata() on a class_device from class_simple_device_add()?

Hi Roland,

Oh thanks, I didnt knew the existance of such possibily.

I once asked here on the list:


Hope this is not a FAQ.

I want to export some read-only attributes (statistics) from cyclades.c char
driver to userspace via sysfs.

I can't figure out the right place to do it - I could create a class under
/sys/class/cyclades for example, but that doesnt sound right since this
is not a "class" of device, but a device itself.

Hooking the statistics into /sys/class/tty/ttyC$/ sounds reasonable, but
its not possible it seems because "tty" is a class_simple class, which only implements
the "dev" attribute.

------ Greg answer was:

For a driver only attribute, you want them to show up in the place for
the driver (like under /sys/bus/pci/driver/MY_FOO_DRIVER/). To do that
use the DRIVER_ATTR() and the driver_add_file() functions. For
examples, see the other drivers that use these functions.

But I hope you are right - /sys/class/tty/tty$/
sounds the correct place for those files - I thought a "class_tty"
class was required for new attributes.

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