Hi, everyoneI 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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