Linux sysfs device_attribute

/***************************************************************************
 *                    Linux sysfs device_attribute
 * 声明：
 *     本文主要是记录linux驱动中如何在sysfs中生成设备属性。
 *
 *                                         2016-2-22 深圳 南山平山村 曾剑锋
 **************************************************************************/                        

static ssize_t show_firmware_version(struct device *dev,            <----------+
        struct device_attribute *attr, char *buf)                              |
{                                                                              |
    struct bq27x00_device_info *di = dev_get_drvdata(dev);                     |
    int ver;                                                                   |
                                                                               |
    ver = bq27x00_battery_read_fw_version(di);                                 |
                                                                               |
    return sprintf(buf, "%d\n", ver);                                          |
}                                                                              |
                                                                               |
static ssize_t show_dataflash_version(struct device *dev,           <----------*-+
        struct device_attribute *attr, char *buf)                              | |
{                                                                              | |
    struct bq27x00_device_info *di = dev_get_drvdata(dev);                     | |
    int ver;                                                                   | |
                                                                               | |
    ver = bq27x00_battery_read_dataflash_version(di);                          | |
                                                                               | |
    return sprintf(buf, "%d\n", ver);                                          | |
}                                                                              | |
                                                                               | |
static ssize_t show_device_type(struct device *dev,                <-----------*-*-+
        struct device_attribute *attr, char *buf)                              | | |
{                                                                              | | |
    struct bq27x00_device_info *di = dev_get_drvdata(dev);                     | | |
    int dev_type;                                                              | | |
                                                                               | | |
    dev_type = bq27x00_battery_read_device_type(di);                           | | |
                                                                               | | |
    return sprintf(buf, "%d\n", dev_type);                                     | | |
}                                                                              | | |
                                                                               | | |
static ssize_t show_reset(struct device *dev,                       <----------*-*-*-+
        struct device_attribute *attr, char *buf)                              | | | |
{                                                                              | | | |
    struct bq27x00_device_info *di = dev_get_drvdata(dev);                     | | | |
                                                                               | | | |
    bq27x00_battery_reset(di);                                                 | | | |
                                                                               | | | |
    return sprintf(buf, "okay\n");                                             | | | |
}                                                                              | | | |
                                                                               | | | |
static DEVICE_ATTR(fw_version, S_IRUGO, show_firmware_version, NULL);   <------+ | | |
static DEVICE_ATTR(df_version, S_IRUGO, show_dataflash_version, NULL);  <------|-+ | |
static DEVICE_ATTR(device_type, S_IRUGO, show_device_type, NULL);       <------|-|-+ |
static DEVICE_ATTR(reset, S_IRUGO, show_reset, NULL);                   <------|-|-|-+
                                                                               | | | |
static struct attribute *bq27x00_attributes[] = {              <---------+     | | | |
    &dev_attr_fw_version.attr,                                  ---------*-----+ | | |
    &dev_attr_df_version.attr,                                  ---------*-------+ | |
    &dev_attr_device_type.attr,                                 ---------*---------+ |
    &dev_attr_reset.attr,                                       ---------*-----------+
    NULL                                                                 |
};                                                                       |
                                                                         |
static const struct attribute_group bq27x00_attr_group = {     <---------*------+
    .attrs = bq27x00_attributes,                                   ------+      |
};                                                                              |
                                                                                |
static int __init bq27x00_battery_probe(struct i2c_client *client,              |
                 const struct i2c_device_id *id)                                |
{                                                                               |
    ......                                                                      |
    retval = sysfs_create_group(&client->dev.kobj, &bq27x00_attr_group); -------+
    if (retval)
        dev_err(&client->dev, "could not create sysfs files\n");                                    

    return ;
    ......
}                                                                                                   

/**
 *  root@android:/sys/bus/i2c/devices/2-0055 # ls
 *  device_type
 *  df_version
 *  driver
 *  fw_version
 *  modalias
 *  name
 *  power
 *  power_supply
 *  reset
 *  subsystem
 *  uevent
 *  root@android:/sys/bus/i2c/devices/2-0055 #
 */