On Wed, Sep 30, 2009 at 6:38 PM, Denis Borisevich <[email protected]>wrote:
> Hi!
> I want to use poll() functionality (to properly handle select() and
> poll() syscalls) in my char-device driver. The code for my kernel-side
> poll() function is (a little bit simplified):
>
> unsigned int my_poll(struct file *filp, struct poll_table_struct *wait)
> {
> unsigned int mask=0;
> unsigned long flags;
>
> poll_wait(filp, my_wait_queue, wait);
>
> if ( any_data_available > 0)
> mask |= POLLIN | POLLRDNORM;
>
> return mask;
> }
>
> Where "my_wait_queue" is of "wait_queue_head_t" type,
> "any_data_available" if the flag which tells if any data is available
> within internal buffer.
>
> When you are setting 'any_data_available' variable to some positive values
at the same place you have to wakeup process that is waiting in wait-queue.
May be this part is missing in your current code and because of that select
is not retuning before timeout.
> When I load this driver and start user-space application wich calls
> select() with 5 seconds timeout the select() returns after waiting
> this timeout no matter when the data comes into the port (1,2,3
> seconds). The return value is positive when the data available and 0
> when no data comes, as it should be. The question is why select()
> waits for the timeout even when data is available?
>
> --
> Denis
>
> Thanks,
Chetan Nanda
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>
