Creating attributes in sysfs

The sysfs allow User space kernel space simple communication  .

The code

#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>
/*
 * The module demonstrats creating 2 attributes in a subdirectory of sysfs.
 *  ls the /sys/kernel/mykobject  
 */
static int intValue = 0;
static char  TxtBuffer[50];
static ssize_t attr_show(struct kobject *kobj, struct kobj_attribute *attr,
        char *buf)
{
 if (strcmp(attr->attr.name, "TxtBuffer") == 0)
 {
  return sprintf(buf, "%s\n", TxtBuffer);
 }
 
 if (strcmp(attr->attr.name, "intValue") == 0)
 {
  return sprintf(buf, "%d\n", intValue);
 }
 
 return 0;
}
static ssize_t attr_store(struct kobject *kobj, struct kobj_attribute *attr,
         const char *buf, size_t count)
{
 
 if (strcmp(attr->attr.name, "TxtBuffer") == 0)
 {
  strcpy (TxtBuffer, buf);
  return count;
 }
 
 if (strcmp(attr->attr.name, "intValue") == 0)
 {
  int theTmpVar;
  sscanf(buf, "%du", &theTmpVar);
  intValue = theTmpVar;
  return count;
 }
 return 0;
}
static struct kobj_attribute intValue_attribute =
 __ATTR(intValue, 0666, attr_show, attr_store);
 
static struct kobj_attribute TxtBuffer_attribute =
 __ATTR(TxtBuffer, 0666, attr_show, attr_store);
 
static struct attribute *attrs[] = {
 &intValue_attribute.attr,
 &TxtBuffer_attribute.attr,
 NULL, 
};
static struct attribute_group attr_group = {
 .attrs = attrs,
  .name = NULL,   /* we want them in the same directory */
};
static struct kobject *mykobject;
static int mykobject_init(void)
{
 int retval;
 mykobject = kobject_create_and_add("mykobject", kernel_kobj);
 if (!mykobject)
  return -ENOMEM;
 
 retval = sysfs_create_group(mykobject, &attr_group);
 if (retval)
  kobject_put(mykobject);
 return retval;
}
static void mykobject_exit(void)
{
 kobject_put(mykobject);
}
module_init(mykobject_init);
module_exit(mykobject_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Zvika Peer  <zvikapeer@hotmail.com>");

After installing the module using insmod let test it. The module directory is :
ls  /sys/kernel/

Inspecting  the mykobject attributes
zvika@zvika-Linux:~/Learn/Drivers/HelloWorld$ ls  /sys/kernel/mykobject
intValue  TxtBuffer

Inserting Data into the attributes:

zvika@zvika-Linux:~/Learn/Drivers/HelloWorld$ sudo echo "Hello zvika" > /sys/kernel/mykobject/TxtBuffer
zvika@zvika-Linux:~/Learn/Drivers/HelloWorld$ sudo echo 164  > /sys/kernel/mykobject/intValue

Retrieving the data back from the attributes:

zvika@zvika-Linux:~/Learn/Drivers/HelloWorld$ sudo cat  /sys/kernel/mykobject/intValue
164
zvika@zvika-Linux:~/Learn/Drivers/HelloWorld$ sudo cat  /sys/kernel/mykobject/TxtBuffer
Hello zvika