2009/9/30 Chetan Nanda <[email protected]>: > > > 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. Thank you for the answer. I got the point. I used this approach when I was implementing read() function in this driver. But in that case I've put the process to sleep manually by wait_event() call. Why do we need this poll_wait() function if we can use wait_event()? I don't see any conveniences which it could give. Or do I miss something? >> >> 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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