[PATCH 5/8] sync_file: add support for a semaphore object

[Chris Wilson]

On Wed, Apr 12, 2017 at 09:01:32PM +0100, Chris Wilson wrote:
> On Thu, Apr 13, 2017 at 05:05:27AM +1000, Dave Airlie wrote:
> > >>
> > >> Not sure what the best semantics are there, any opinions on barring
> > >> wakeups/polling on semaphore sync_files, and just punting this
> > >> until we need it.
> > >
> > > I think getting it right now will make writing sw_sync-esque (i.e. cpu)
> > > tests easier and more complete.
> > 
> > I just don't have any use case for it, so we would be writing code to
> > write tests for it.
> > 
> > That doesn't seem smart.
> > 
> > If there is a future non-testing use case, the API is expressive
> > enough for someone
> > to add a flag or new sync obj to allow polling and to add support in a
> > nice easily
> > digestible patch.
> 
> My first thought was to check the signaled status would be to use
> poll(0), but that can be retrieved from the sync_file_status ioctl. But
> to get that still needs for us to acquire an fd from the syncobj. And if
> we were to want check the flag on a driver syncobj, we would need to be
> able to export one. That doesn't look very promising...

Hmm, you do export fd to pass syncobj between processes. Let's not start
with syncobj being a second class sync_file.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre