Okay, this was a long time pending task. I wanted to learn how to make the sysfs entry. I was always deferring this task as it was a bit boring. The alternative I had was of using procfs. Finally from a nice article and some r&d in kernel code lead me to write this sample code.
Source Link : http://people.ee.ethz.ch/~arkeller/linux/kernel_user_space_howto.html#ss2.3
The code provided in the link doesn’t work for kernel version 2.6.38.2. I have modified it a bit to make it work with latest kernel, but it makes the top level entry under /sys – but it’s okay for learning purpose.
Here is the code,
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
struct my_attr {
struct attribute attr;
int value;
};
static struct my_attr my_first = {
.attr.name="first",
.attr.mode = 0644,
.value = 1,
};
static struct my_attr my_second = {
.attr.name="second",
.attr.mode = 0644,
.value = 2,
};
static struct attribute * myattr[] = {
&my_first.attr,
&my_second.attr,
NULL
};
static ssize_t default_show(struct kobject *kobj, struct attribute *attr,
char *buf)
{
struct my_attr *a = container_of(attr, struct my_attr, attr);
return scnprintf(buf, PAGE_SIZE, "%d\n", a->value);
}
static ssize_t default_store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t len)
{
struct my_attr *a = container_of(attr, struct my_attr, attr);
sscanf(buf, "%d", &a->value);
return sizeof(int);
}
static struct sysfs_ops myops = {
.show = default_show,
.store = default_store,
};
static struct kobj_type mytype = {
.sysfs_ops = &myops,
.default_attrs = myattr,
};
struct kobject *mykobj;
static int __init sysfsexample_module_init(void)
{
int err = -1;
mykobj = kzalloc(sizeof(*mykobj), GFP_KERNEL);
if (mykobj) {
kobject_init(mykobj, &mytype);
if (kobject_add(mykobj, NULL, "%s", "sysfs_sample")) {
err = -1;
printk("Sysfs creation failed\n");
kobject_put(mykobj);
mykobj = NULL;
}
err = 0;
}
return err;
}
static void __exit sysfsexample_module_exit(void)
{
if (mykobj) {
kobject_put(mykobj);
kfree(mykobj);
}
}
module_init(sysfsexample_module_init);
module_exit(sysfsexample_module_exit);
MODULE_LICENSE("GPL");
Have fun!!
everyone is waiting …
be topa..use lj…all other are crap…
LOL. I saw your comment today!
really a awesome source code for beginners of the KOBJECT , Thanks for sharing
I was really having a hard time learning sysfs…and in the book LDD 3rd edition the code is outdated…Thanks for the modification for latest kernel and sharing