[libcamera-devel,v4,11/11] libcamera: camera: Lock the pipeline handler in acquire()

1216 diff mbox series

To allow more than one application using libcamera simultaneously there
can be no overlap between which cameras are in use by which user. As a
camera is part of a pipeline handler and there might be shared resources
between all cameras exposed by that pipeline handler it's not enough to
to only lock access to a single camera, all cameras from that pipeline
need to be tied to the same process.

Allow for this by locking the whole pipeline when one of its cameras
is acquired by the user. Other processes can still enumerate and list
all cameras in the system but can't acquire a camera from a locked
pipeline handler.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
---
 src/libcamera/camera.cpp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

Hi Niklas,

Thank you for the patch.

On Fri, May 17, 2019 at 02:54:47AM +0200, Niklas Söderlund wrote:
> To allow more than one application using libcamera simultaneously there
> can be no overlap between which cameras are in use by which user. As a
> camera is part of a pipeline handler and there might be shared resources
> between all cameras exposed by that pipeline handler it's not enough to
> to only lock access to a single camera, all cameras from that pipeline
> need to be tied to the same process.
> 
> Allow for this by locking the whole pipeline when one of its cameras
> is acquired by the user. Other processes can still enumerate and list
> all cameras in the system but can't acquire a camera from a locked
> pipeline handler.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
> ---
>  src/libcamera/camera.cpp | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp
> index cb45bafe3fb1ff85..a83768fcde126c32 100644
> --- a/src/libcamera/camera.cpp
> +++ b/src/libcamera/camera.cpp
> @@ -470,13 +470,17 @@ void Camera::disconnect()
>   * not blocking, if the device has already been acquired (by the same or another
>   * process) the -EBUSY error code is returned.
>   *
> + * Acquiring a camera will limit usage of any other camera(s) provided by the
> + * same pipeline hander to the same instance of libcamera. The limit is in

s/hander/handler/

> + * effect until all cameras from the pipeline handler are released(). Other

"released" isn't a function, you should write "released" or "released
with release()". As the release() function is mentioned elsewhere in
this documentation block, I would leave it out here.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> + * instances of libcamera can still list and examine the cameras but will fail
> + * if they attempt to acquire() any of them.
> + *
>   * Once exclusive access isn't needed anymore, the device should be released
>   * with a call to the release() function.
>   *
>   * This function affects the state of the camera, see \ref camera_operation.
>   *
> - * \todo Implement exclusive access across processes.
> - *
>   * \return 0 on success or a negative error code otherwise
>   * \retval -ENODEV The camera has been disconnected from the system
>   * \retval -EBUSY The camera is not free and can't be acquired by the caller
> @@ -489,6 +493,12 @@ int Camera::acquire()
>  	if (!stateIs(CameraAvailable))
>  		return -EBUSY;
>  
> +	if (!pipe_->lock()) {
> +		LOG(Camera, Info)
> +			<< "Pipeline handler in use by another process";
> +		return -EBUSY;
> +	}
> +
>  	state_ = CameraAcquired;
>  
>  	return 0;
> @@ -510,6 +520,8 @@ int Camera::release()
>  	if (!stateBetween(CameraAvailable, CameraConfigured))
>  		return -EBUSY;
>  
> +	pipe_->unlock();
> +
>  	state_ = CameraAvailable;
>  
>  	return 0;