device_create分析

水深无声 2022-09-24 05:27 144阅读 0赞

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。

device_create分析

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