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Old 04-26-2013, 03:35 PM   #1
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Registered: Apr 2013
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How to create a simple sysfs class attribute in Linux kernel v3.2

I'm learning how to use sysfs in my Linux modules, but I'm having the hardest time finding current documentation on these topics. The Linux Device Drivers 3rd Edition book I've been using seems to be rather dated in this area unfortunately (e.g. the class_device appears to be completely gone in current Linux versions).

I'm simply trying to get an attribute to appear, under the respective sysfs class for my module, that will allow me to read the value of a module variable from kernel space.

In my code, I have a class created that allows udev to create a device node at /dev/foo for my module:
dev_t foo_dev;
alloc_chrdev_region(&foo_dev, 0, 1, "bar");

struct class *bar = class_create(THIS_MODULE, "bar");

device_create(bar, NULL, foo_dev, NULL, "foo");

struct cdev foo_dev_file;
cdev_init(&foo_dev_file, &fops); /* fops defined earlier */
cdev_add(&foo_dev_file, foo_dev, 1);
When I insert the module I get a sysfs class directory created and populated with some default attributes at /sys/class/bar/foo/. How can I create attributes that show up under this new directory?

I have the concepts down pretty well I believe -- create attribute structure, define sysfs_ops functions, etc -- my problem is that I don't know which particular kernel structure to use (class_attribute?), nor how to make these attributes appear under the right sysfs directory.

Would anyone point me to a tutorial or article detailing the process for current Linux kernels?

Last edited by vilhelmgray; 04-29-2013 at 08:01 AM.
Old 04-29-2013, 08:00 AM   #2
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Registered: Apr 2013
Posts: 4

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I figured out that I can use the class_create_file function after the class_create call to make a class attribute appear under my class directory.

class_create_file(bar, my_foobar_attr);
Assuming my_foobar_attr is a pointer to a defined class_attribute structure, that line will make the class attribute appear under /sys/class/bar/.

Use the device_create_file function to add attribute files under the foo device directory.

Last edited by vilhelmgray; 04-29-2013 at 01:40 PM.


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