The code for implementing our sysfs file and its callbacks

Let's look at the relevant parts of the code for our simple sysfs interfacing driver and try things out, step by step:

1. Set up the device attribute structure (via the DEVICE_ATTR_RW macro; see the preceding section for more information) and create our first sysfs (pseudo) file:

// ch2/sysfs_simple_intf/sysfs_simple_intf.c

#define SYSFS_FILE1 llkdsysfs_debug_level
// [... <we show the actual read/write callback functions just a bit further down> ...]
static DEVICE_ATTR_RW(SYSFS_FILE1);

int __init sysfs_simple_intf_init(void)
{
 [...]
/* << 0. The platform device is created via the platform_device_register_simple() API; code already shown above ... >> */

 // 1. Create our first sysfile file : llkdsysfs_debug_level
 /* The device_create_file() API creates a sysfs attribute file for
  * given device (1st parameter); the second parameter is the pointer
  * to it's struct device_attribute structure dev_attr_<name...