[Linux]Attribute

有 DRIVER_ATTR 和 DEVICE_ATTR 兩種

Device drivers can export attributes via their sysfs directories.
Drivers can declare attributes using a DRIVER_ATTR macro that works
identically to the DEVICE_ATTR macro.

macro定義如下
#define DEVICE_ATTR(_name, _mode, _show, _store) \
struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
#define DRIVER_ATTR(_name, _mode, _show, _store) \
struct driver_attribute driver_attr_##_name = \
__ATTR(_name, _mode, _show, _store)
例如:
static DRIVER_ATTR(i2c,  S_IWUSR | S_IRUGO, show_register_value,  store_register_value);


這些mode的值，定義在kernel/include/linux/stat.h
S_IRUGO=(S_IRUSR | S_IRGRP | S_IROTH)
S_IRUSR：00400 表示user read
S_IRGRP：00040 表示group read
S_IROTH：00004 表示other read


通常會定義attribute的路徑，例如
#define BLUETOOTH_POWER_PATH "/sys/module/bluetooth_power/parameters/power"
#define SE123_POWER_PATH "/sys/class/misc/ssiscan/power_en"

然後會有個function如下去enable power
static int set_se655_power(int on) {
    int ret = -1;
    int sz;
    const char buffer = (on ? 'Y' : 'N');
    int fd = open(SE655_POWER_PATH, O_WRONLY);

這些mode的值，定義在kernel/include/asm-generic/fcntl.h
#define O_RDONLY 00000000
#define O_WRONLY 00000001


在kernel/include/linux/device.h裡面定義了以下幾種attribute類型
Bus_attribute
Device_attribute
Driver_attribute
Class_attribute
Dev_ext_attribute
Bin_attribute

Reference:
http://www.bitscn.com/os/linux/200904/158631_7.html