Linux Device Drivers Development

Steps to poll

When you implement the poll function, either the read or write method may change:

1. Declare a wait queue for each event type (read, write, exception) you need to implement passive wait, to put tasks in when there is no data to read, or when the device is not yet writable:

static DECLARE_WAIT_QUEUE_HEAD(my_wq); 
static DECLARE_WAIT_QUEUE_HEAD(my_rq); 

2. Implement the poll function like this:

#include <linux/poll.h> 
static unsigned int eep_poll(struct file *file, poll_table *wait) 
{ 
    unsigned int reval_mask = 0; 
    poll_wait(file, &my_wq, wait); 
    poll_wait(file, &my_rq, wait); 
 
    if (new-data-is-ready) 
        reval_mask |= (POLLIN | POLLRDNORM); 
    if (ready_to_be_written) 
       reval_mask |= (POLLOUT | POLLWRNORM); 
    return reval_mask; 
} 

3. Notify the wait ...