Re: character driver - poll() timeout

[Clemens Ladisch <clemens@ladisch.de>]

Muni Sekhar wrote:
> On Tue, Oct 27, 2015 at 8:48 PM, Clemens Ladisch <clemens@ladisch.de> wrote:
>> Muni Sekhar wrote:
>>> I need to find out when exactly driver's poll callback returned timeout.
>>
>> Your poll callback _cannot_ return a timeout.
>>
>> Why do you think you need this information for?
>
> During stress test, my test application fails and throws poll() timeout error.
>
> I need to debug what is the state of my driver during that time. I
> added prints in driver poll(), but I gets lots of debug prints if
> poll() timeout is more.

Your poll() callback does not really change the state of the driver.
It just returns the wait queue and the current state of the device.
(Which means it is likely to get called _twice_, before poll() goes
to sleep, and just before it returns.)

Your driver's state changes only when
1) you start some operation (such as read() or write()), or when
2) you finish some operation (which wakes up anyone waiting on
   that wait queue).

If you time out, it means that some wake_up() happens too late or
not at all, or that you do not return the correct state.


Regards,
Clemens