Static Device_attr (val, S_irugo | S_IWUSR, Hello_val_show, Hello_val_store); The role

In Lao Luo's Android routines there are

Static Device_attr (val, S_irugo | S_IWUSR, Hello_val_show, Hello_val_store);

/* Read Device properties val*/

• Static ssize_t hello_val_show (struct device* dev, struct device_attribute* attr, char* buf) {
• struct hello_android_dev* Hdev = (struct hello_android_dev*) dev_get_drvdata (dev);
• return __hello_get_val (Hdev, buf);
• }
• /* Write device Properties val*/
• Static ssize_t Hello_val_store (struct device* dev, struct device_attribute* attr, const char* buf, si ze_t count) {
• struct hello_android_dev* Hdev = (struct hello_android_dev*) dev_get_drvdata (dev);
• return __hello_set_val (Hdev, buf, Count);
• }

In this way, you can change/display the value of the Val variable in the serial terminal

# Cat Hello
0
# echo ' 5 ' > Hello
# # echo ' 5 ' > Hello # cat Hello
5

The original is static Device_attr (val, S_irugo | S_IWUSR, Hello_val_show, Hello_val_store);

The role

Prototypes are # define DEVICE_ATTR (_name, _mode, _show, _store) \

struct Device_attribute dev_attr_# #_name = __attr (_name, _mode, _show, _store)

The function macro device_attr is encapsulated in the __attr (_name,_mode,_show,_stroe) method, _show represents the Read method, and _stroe represents the Write method.

When we echo the data into the interface, we actually complete a write operation on the upper layer, which corresponds to kernel, and calls the "store" in the driver. Similarly, "show" is called when we have a cat interface. Here, simply built the android layer to the kernel bridge, the actual implementation of the hardware operation, or in the "show" and "store" completed

Static Device_attr (val, S_irugo | S_IWUSR, Hello_val_show, Hello_val_store); The role