目標：初始化一個攝像頭等待佇列頭cam_wait_queue

實現：static  DECLARE_WAIT_QUEUE_HEAD(cam_wait_queue)

使用：wait_event_interruptible(cam_wait_queue,ev_cam);

wait_up_interuptible(&cam_wait_queue);

解釋：

include/linux/wait.h
#define DECLARE_WAIT_QUEUE_HEAD(name) \
	wait_queue_head_t name = __WAIT_QUEUE_HEAD_INITIALIZER(name)
 

初始化佇列頭name，name結構體：

struct __wait_queue_head {
	spinlock_t lock;
	struct list_head task_list;
};

對結構體的兩個引數初始化：

#define __WAIT_QUEUE_HEAD_INITIALIZER(name) {				\
	.lock		= __SPIN_LOCK_UNLOCKED(name.lock),		\
	.task_list	= { &(name).task_list, &(name).task_list } }

先看第二個引數task_list定義：

struct list_head {
	struct list_head *next, *prev;
};
 

這裡lock引數的結構體我簡化了一下，只保留了結構體中的一個引數。

lock結構體：

typedef struct spinlock {
	union {
		struct raw_spinlock rlock;
	};
} spinlock_t;

初始化：

#define __SPIN_LOCK_UNLOCKED(lockname) \
	(spinlock_t ) __SPIN_LOCK_INITIALIZER(lockname)

#define __SPIN_LOCK_INITIALIZER(lockname) \
	{ { .rlock = __RAW_SPIN_LOCK_INITIALIZER(lockname) } }
 

#define __RAW_SPIN_LOCK_INITIALIZER(lockname)	\
	{					\
	.raw_lock = __ARCH_SPIN_LOCK_UNLOCKED,	\
	 }

一路追蹤下來，最終

.lock.raw_lock= __ARCH_SPIN_LOCK_UNLOCKED

typedef struct raw_spinlock {
	arch_spinlock_t raw_lock;
} raw_spinlock_t;