[libcamera-devel] [RFC 09/11] libcamera: media_device: Add functions to lock device for other processes

[Laurent Pinchart]

Hi Niklas,

Thank you for the patch.

On Sun, Apr 14, 2019 at 03:35:04AM +0200, Niklas Söderlund wrote:
> Add lock() and unlock() which backed by lockf() allows an instance of
> libcamera to claim exclusive access to a media device. These functions
> is the base to allow multiple users of libcamera to coexist in the
> system without stepping on each others toes.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> ---
>  src/libcamera/include/media_device.h |  4 ++++
>  src/libcamera/media_device.cpp       | 29 +++++++++++++++++++++++++++-
>  2 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/include/media_device.h b/src/libcamera/include/media_device.h
> index 5d28a7bb8214ef4a..e2956549fa201ea3 100644
> --- a/src/libcamera/include/media_device.h
> +++ b/src/libcamera/include/media_device.h
> @@ -64,6 +64,10 @@ private:
>  	bool acquire();
>  	void release();
>  
> +	bool lockOwner_;
> +	bool lock();
> +	void unlock();
> +

We usually put functions first, and variables next.

>  	std::map<unsigned int, MediaObject *> objects_;
>  	MediaObject *object(unsigned int id);
>  	bool addObject(MediaObject *object);
> diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp
> index 46931f52688f6c82..5cea4e63715125c8 100644
> --- a/src/libcamera/media_device.cpp
> +++ b/src/libcamera/media_device.cpp
> @@ -62,7 +62,8 @@ LOG_DEFINE_CATEGORY(MediaDevice)
>   * populate() before the media graph can be queried.
>   */
>  MediaDevice::MediaDevice(const std::string &deviceNode)
> -	: deviceNode_(deviceNode), fd_(-1), valid_(false), acquired_(false)
> +	: deviceNode_(deviceNode), fd_(-1), valid_(false), acquired_(false),
> +	  lockOwner_(false)
>  {
>  }
>  
> @@ -421,6 +422,32 @@ void MediaDevice::release()
>  	acquired_ = false;
>  }
>  
> +bool MediaDevice::lock()

Could you please document those two functions, and especially the pre
and post conditions ?

> +{
> +	if (fd_ == -1)
> +		return false;
> +
> +	if (lockOwner_)
> +		return true;
> +
> +	if (lockf(fd_, F_TLOCK, 0))
> +		return false;
> +
> +	lockOwner_ = true;
> +
> +	return true;
> +}
> +
> +void MediaDevice::unlock()
> +{
> +	if (fd_ == -1)
> +		return;
> +
> +	lockOwner_ = false;
> +
> +	lockf(fd_, F_ULOCK, 0);
> +}
> +
>  /**
>   * \var MediaDevice::objects_
>   * \brief Global map of media objects (entities, pads, links) keyed by their

-- 
Regards,

Laurent Pinchart