device_create分析

device_create分析

2010-11-12 10:46

在2.6比较新的内核里面，这个函数在设备驱动中比较重要，拿出来单独分析下 源码如下： /** * device_create - creates a device and registers it with sysfs * @class: pointer to the struct class that this device should be registered to * @parent: pointer to the parent struct device of this new device, if any * @devt: the dev_t for the char device to be added * @drvdata: the data to be added to the device for callbacks * @fmt: string for the device's name * * This function can be used by char device classes. A struct device * will be created in sysfs, registered to the specified class. * * A "dev" file will be created, showing the dev_t for the device, if * the dev_t is not 0,0. * If a pointer to a parent struct device is passed in, the newly created * struct device will be a child of that device in sysfs. * The pointer to the struct device will be returned from the call. * Any further sysfs files that might be required can be created using this * pointer. * * Note: the struct class passed to this function must have previously * been created with a call to class_create(). */ struct device *device_create(struct class *class, struct device *parent,                           dev_t devt, void *drvdata, const char *fmt, ...) {        va_list vargs;        struct device *dev;        va_start(vargs, fmt);        dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs);        va_end(vargs);        return dev; } 先看参数 @class: pointer to the struct class that this device should be registered to the struct class 指针，必须在本函数调用之前先被创建 parent: pointer to the parent struct device of this new device 该设备的parent指针。 devt: the dev_t for the char device to be added 字符设备的设备号，如果dev_t不是0,0的话，1个”dev”文件将被创建。 drvdata: the data to be added to the device for callbacks 被添加到该设备回调的数据。 fmt: string for the device's name 设备名字。 可以看下面的函数调用例子 例子1 /* register your own device in sysfs, and this will cause udev to create corresponding device node */    device_create( my_class, NULL, MKDEV(hello_major, 0), "hello" "%d", 0 ); 如果成功，它将会在/dev目录下产生/dev/hello0设备。 例子2 led_cdev->dev = device_create_drvdata(leds_class, parent, 0, led_cdev,                                          "%s", led_cdev->name); 这是前文platform之gpio-leds里面的源码 由于dev_t是0，所以它不会在/dev下产生设备文件。 led_cdev为传递给class的私有数据。 会把第6个参数的内容复制到第5个参数 “%s”，就像printf一样。 通过这2个例子，应该对它的用法有所了解了，下面看下源码。 dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs); 深入device_create_vargs /** * device_create_vargs - creates a device and registers it with sysfs * @class: pointer to the struct class that this device should be registered to * @parent: pointer to the parent struct device of this new device, if any * @devt: the dev_t for the char device to be added * @drvdata: the data to be added to the device for callbacks * @fmt: string for the device's name * @args: va_list for the device's name * * This function can be used by char device classes. A struct device * will be created in sysfs, registered to the specified class. * * A "dev" file will be created, showing the dev_t for the device, if * the dev_t is not 0,0. * If a pointer to a parent struct device is passed in, the newly created * struct device will be a child of that device in sysfs. * The pointer to the struct device will be returned from the call. * Any further sysfs files that might be required can be created using this * pointer. * * Note: the struct class passed to this function must have previously * been created with a call to class_create(). */ struct device *device_create_vargs(struct class *class, struct device *parent,                                dev_t devt, void *drvdata, const char *fmt,                                va_list args) {        struct device *dev = NULL;        int retval = -ENODEV;        if (class == NULL || IS_ERR(class))               goto error;        dev = kzalloc(sizeof(*dev), GFP_KERNEL);        if (!dev) {               retval = -ENOMEM;               goto error;        }        dev->devt = devt;        dev->class = class;        dev->parent = parent;        dev->release = device_create_release;        dev_set_drvdata(dev, drvdata);        vsnprintf(dev->bus_id, BUS_ID_SIZE, fmt, args);        retval = device_register(dev);        if (retval)               goto error;        return dev; error:        kfree(dev);        return ERR_PTR(retval); } 代码比较容易，最灵活的在这个地方 vsnprintf(dev->bus_id, BUS_ID_SIZE, fmt, args); vsnprintf()会根据参数fmt字符串来转换并格式化数据，然后将结果复制到数组dev->bus_id所指的字符串数组，知道出现字符串结束符或达到参数BUS_ID_SIZE为止