[libcamera-devel] [PATCH v4 5/8] libcamera: v4l2_videodevice: Better tracking of the device state

[Laurent Pinchart]

On Wed, Mar 23, 2022 at 09:59:02AM +0000, Kieran Bingham via libcamera-devel wrote:
> Quoting Naushir Patuck via libcamera-devel (2022-03-22 09:22:54)
> > Replace the existing streaming_ state variable with an enum to track the
> > following three state: Streaming, Stopping, and Stopped. The alternate states
> > will be used in a subsequent commit.
> > 
> > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > ---
> >  include/libcamera/internal/v4l2_videodevice.h |  3 ++-
> >  src/libcamera/v4l2_videodevice.cpp            | 10 ++++++----
> >  2 files changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
> > index 2d2ccc477c91..32e022543385 100644
> > --- a/include/libcamera/internal/v4l2_videodevice.h
> > +++ b/include/libcamera/internal/v4l2_videodevice.h
> > @@ -258,7 +258,8 @@ private:
> >  
> >         EventNotifier *fdBufferNotifier_;
> >  
> > -       bool streaming_;
> > +       enum class State { Streaming, Stopping, Stopped };
> > +       State state_;
> >  };
> >  
> >  class V4L2M2MDevice
> > diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> > index 5f36ee20710d..9cea6a608660 100644
> > --- a/src/libcamera/v4l2_videodevice.cpp
> > +++ b/src/libcamera/v4l2_videodevice.cpp
> > @@ -507,7 +507,7 @@ const std::string V4L2DeviceFormat::toString() const
> >   */
> >  V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
> >         : V4L2Device(deviceNode), formatInfo_(nullptr), cache_(nullptr),
> > -         fdBufferNotifier_(nullptr), streaming_(false)
> > +         fdBufferNotifier_(nullptr), state_(State::Stopped)
> >  {
> >         /*
> >          * We default to an MMAP based CAPTURE video device, however this will
> > @@ -1796,7 +1796,7 @@ int V4L2VideoDevice::streamOn()
> >                 return ret;
> >         }
> >  
> > -       streaming_ = true;
> > +       state_ = State::Streaming;
> >  
> >         return 0;
> >  }
> > @@ -1818,7 +1818,7 @@ int V4L2VideoDevice::streamOff()
> >  {
> >         int ret;
> >  
> > -       if (!streaming_ && queuedBuffers_.empty())
> > +       if (state_ != State::Streaming && queuedBuffers_.empty())
> >                 return 0;
> >  
> >         ret = ioctl(VIDIOC_STREAMOFF, &bufferType_);
> > @@ -1828,6 +1828,8 @@ int V4L2VideoDevice::streamOff()
> >                 return ret;
> >         }
> >  
> > +       state_ = State::Stopping;
> > +
> 
> Should this be before the call for VIDIOC_STREAMOFF?
> It may not make a difference in practice, or it might cause
> V4L2VideoDevice to reject a buffer (/request) that is queued in parallel
> ... but I think we already know the request can be queued while calling
> streamOff ... so I 'think' it's safe to change the state before calling
> the ioctl...

As the V4L2VideoDevice class isn't thread-safe, it will indeed make no
difference. I'd rather keep it here, or the state will stay Stopping
forever if VIDIOC_STREAMOFF fails.

> Which ever way you're happier with, or consensus goes to:
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> >         /* Send back all queued buffers. */
> >         for (auto it : queuedBuffers_) {
> >                 FrameBuffer *buffer = it.second;
> > @@ -1838,7 +1840,7 @@ int V4L2VideoDevice::streamOff()
> >  
> >         queuedBuffers_.clear();
> >         fdBufferNotifier_->setEnabled(false);
> > -       streaming_ = false;
> > +       state_ = State::Stopped;
> >  
> >         return 0;
> >  }

-- 
Regards,

Laurent Pinchart