Linux Device Drivers Development

Wait queue

Wait queues are essentially used to process blocked I/O, to wait for particular conditions to be true, and to sense data or resource availability. To understand how they work, let's have a look at their structure in include/linux/wait.h:

struct __wait_queue { 
    unsigned int flags; 
#define WQ_FLAG_EXCLUSIVE 0x01 
    void *private; 
    wait_queue_func_t func; 
    struct list_head task_list; 
}; 

Let's pay attention to the task_list field. As you can see, it is a list. Every process you want to put to sleep is queued in that list (hence the name wait queue) and put into a sleep state until a condition becomes true. The wait queue can be seen as nothing but a simple list of processes and a lock.

The functions you will always face when dealing with ...