Hi, everyone
I am implementing a simple driver to experiment with wait queue.Two or more read processes block until a write process changes a flag and call wake_up_interruptible().I expect that a write process will only wake up one read process.However, once a write process calls wake_up_interruptible() , all the read processes are awaken. How can I wake up one process from the wait queue? Here is the snippet of the simple dirver(just for experimenting, kernel 2.6.18):
static ssize_t rlwait_read(struct file *filp, char __user *userp, size_t size, loff_t *off)
{
struct rlwait_t *rock = (struct rlwait_t *)filp->private_data;
DECLARE_WAITQUEUE(wait, current);
add_wait_queue(&rock->r_wait_head, &wait);
while (rock->r_flag == 0) {
set_current_state(TASK_INTERRUPTIBLE);
schedule();
}
remove_wait_queue(&rock->r_wait_head, &wait);
set_current_state(TASK_RUNNING);
return 0;
}
static ssize_t rlwait_write(struct file *filp, const char __user *userp, size_t size, loff_t *off)
{
struct rlwait_t *rock = (struct rlwait_t *)filp->private_data;
rock->r_flag = 1;
wake_up_interruptible(&rock->r_wait_head);
return size;
}
Thans in advice.
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