container_of()宏

指標ptr指向結構體type中的成員member；通過指標ptr，返回結構體type的起始地址
          type
      |----------|
      |          |
      |          |
      |----------|
ptr-->| member --|
      |----------|
      |          |
      |          |
      |----------|
/**
* container_of - cast a member of a structure out to the containing structure
* @ptr:    the pointer to the member.
* @type:   the type of the container struct this is embedded in.
* @member: the name of the member within the struct.
* */

#define container_of(ptr, type, member) ({                    /       
        const typeof( ((type *)0)->member ) *__mptr = (ptr); -/
        (type *)( (char *)__mptr - offsetof(type,member) );})

--------------------------------------------------
d = usb_device->dev.driver
container_of(d, struct usb_device_driver, drvwrap.driver)

     struct usb_device
|----------------------------|
|                            |
|                            |
|----------------------------|
|                            | struct device
|struct device_driver *driver|--+
|                            | -|
|----------------------------| -|
|                            | -|
|                            | -|
|----------------------------| -|
                                |
+-------------------------------+
|
|    struct usb_device_driver
| --|---------------------------|
|-- |                           |
|-- |                           |
| --|---------------------------|
+-->|struct device_driver driver| struct usbdrv_wrap drvwrap
    |int             for_devices|
    |---------------------------|
    |                           |
    |---------------------------|

 

 

--------------------------------------------container_of宏，它的功能是得到包含某個結構成員的結構的指標: 其實現如下： #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)#define container_of(ptr, type, member) ({                      /        const typeof( ((type *)0)->member ) *__mptr = (ptr);    /        (type *)( (char *)__mptr - offsetof(type,member) );})     分析可知__mptr指向的是一個type結構裡typeof(((type *)0)->member)類型member成員的指標，offsetof(type,member)是這個成員在結構中的位移，單位是位元組，所以為了計算type結構的起始地址，__mptr減去它自己的位移。