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

[Kieran Bingham]

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...

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;
>  }
> -- 
> 2.25.1
>