指针ptr指向结构体type中的成员member；通过指针ptr，返回结构体type的起始地址
type
|----------|
| |
| |
|----------|
ptr-->| member --|
|----------|
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|----------|
/**
* 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个结构成员的结构的指针:
其实现如下：
#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指向的是一个type结构里typeof(((type
*)0)->member)类型member成员的指针，offsetof(type,member)是这个成员在结构中的偏移，单位是字节，所以
为了计算type结构的起始地址，__mptr减去它自己的偏移。
