2009/9/30 Daniel Baluta <daniel.baluta@xxxxxxxxx>:
> On Wed, Sep 30, 2009 at 7:24 PM, Chetan Nanda <chetannanda@xxxxxxxxx> wrote:
>>
>>
>> On Wed, Sep 30, 2009 at 6:38 PM, Denis Borisevich <dennisfen@xxxxxxxxx>
>> 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.
>
> This is not true. You only have to set "data_available" in mask and
> return it. An upper
> layer will take care about waking up the process that is waiting in wait-queue.
>
>>
>>
>>>
>>> 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?
> What about select without a timeout? Does the call ever return?
With timeout set to NULL the call never returns.
> Daniel.
>
--
Denis
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