Re: [PATCH v5 5/6] V4L: Events: Support event handling in do_ioctl

[Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>]

Laurent Pinchart wrote:
> Hi Sakari,

Salut Laurent,

>>> There is a crucial piece of functionality missing here: if the filehandle
>>> is in blocking mode, then it should wait until an event arrives. That
>>> also means that if vfh->events == NULL, you should still call
>>> v4l2_event_dequeue, and that function should initialize vfh->events and
>>> wait for an event if the fh is in blocking mode.
>>
>> I originally left this out intentionally. Most applications using events
>> would use select / poll as well by default. For completeness it should
>> be there, I agree.
>>
>> This btw. suggests that we perhaps should put back the struct file
>> argument for the event functions in video_ioctl_ops. The blocking flag
>> is indeed part of the file structure. I'm open to better suggestions, too.
> 
> If the only information we need from struct file is the flags, they could be 
> copied to v4l2_fh in the open handler. We could also put a struct file * 
> member in v4l2_fh.

That could be one possibility. Copying the flags in open() isn't enough
as they can change as a result of fcntl call. As we're not handling that
call the flags in struct v4l2_fh would have to be updated for every
ioctl. I'm not a big fan of caching information in general either. :-) I
could accept this, though.

-- 
Sakari Ailus
sakari.ailus@maxwell.research.nokia.com