[libcamera-devel] [PATCH v7 7/9] libcamera: pipeline: uvcvideo: Generate unique camera names

[Laurent Pinchart]

Hi Niklas,

Thank you for the patch.

On Tue, Aug 04, 2020 at 06:13:56PM +0200, Niklas Söderlund wrote:
> Generate camera names that are unique and persistent between system
> resets. The name is constructed from the USB device information as well
> as the USB controller on the host.
> 
> Before this change example of camera names:
> 
> Venus USB2.0 Camera: Venus USB2
> Logitech Webcam C930e
> 
> After this change the same cameras are:
> 
> \_SB_.PCI0.RP05.PXSX-2.1.1:1.0-0ac8:3420
> \_SB_.PCI0.RP05.PXSX-2.4:1.0-046d:0843
> 
> On OF-based system:
> 
> base/soc/usb at 7e980000/usb-port at 1-1.3:1.0-0ac8:3420
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> ---
> * Changes since v5
> - New algorithm to generate IDs.
> 
> * Changes since v3
> - Switch argument to generateName() to UVCCameraData pointer.
> ---
>  src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 77 +++++++++++++++++++-
>  1 file changed, 76 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> index 93e3dc17e3a7105e..70c057b543f85c7b 100644
> --- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> +++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <algorithm>
> +#include <fstream>
>  #include <iomanip>
>  #include <math.h>
>  #include <tuple>
> @@ -20,6 +21,7 @@
>  #include "libcamera/internal/log.h"
>  #include "libcamera/internal/media_device.h"
>  #include "libcamera/internal/pipeline_handler.h"
> +#include "libcamera/internal/sysfs.h"
>  #include "libcamera/internal/utils.h"
>  #include "libcamera/internal/v4l2_controls.h"
>  #include "libcamera/internal/v4l2_videodevice.h"
> @@ -81,6 +83,8 @@ public:
>  	bool match(DeviceEnumerator *enumerator) override;
>  
>  private:
> +	std::string generateID(const UVCCameraData *data);

s/ID/Id/

> +
>  	int processControl(ControlList *controls, unsigned int id,
>  			   const ControlValue &value);
>  	int processControls(UVCCameraData *data, Request *request);
> @@ -379,6 +383,71 @@ int PipelineHandlerUVC::queueRequestDevice(Camera *camera, Request *request)
>  	return 0;
>  }
>  
> +std::string PipelineHandlerUVC::generateID(const UVCCameraData *data)
> +{
> +	const std::string path = data->video_->devicePath();
> +
> +	/* Creata a device ID from the USB devices vendor and product ID. */
> +	std::string deviceId;
> +	for (const std::string &name : { "idVendor", "idProduct" }) {
> +		std::ifstream file(path + "/../" + name);
> +
> +		if (!file.is_open())
> +			return {};
> +
> +		std::string value;
> +		std::getline(file, value);
> +		file.close();
> +
> +		deviceId += value + (deviceId.empty() ? ":" : "");

		if (!deviceId.empty())
			deviceId += ":";

		deviceId += value;

so this will work with more than two iterations :-)

> +	}

Of course you could also use utils::join() if you wanted.

I'd move this block after the next, to follow the same order as in the
ID string, but maybe it's just me.

> +
> +	/*
> +	 * Create a USB ID from the device path which has the known format:
> +	 *
> +	 *	bus , "-", ports, ":", config, ".", interface ;

s/bus ,/ bus,/ (maybe path = ... ?)

> +	 *	bus = number ;
> +	 *	ports = port, [ ".", ports ] ;
> +	 *	port = number ;
> +	 *	config = number ;
> +	 *	interface = number ;
> +	 *
> +	 * Example: 3-2.4:1.0
> +	 *
> +	 * The bus is not guaranteed to be stable and needs to be stripped from
> +	 * the USB ID. The final USB ID is built up of the ports, config and
> +	 * interface properties.
> +	 *
> +	 * Example 2.4:1.0.
> +	 */
> +	std::string usbId = basename(path.c_str());
> +	usbId = usbId.substr(usbId.find('-') + 1, std::string::npos);

The second argument defaults to std::string::npos, so you could leave it
out if you wanted.

> +
> +	/* Create a controller ID from first device described in firmware. */
> +	std::string controllerId;
> +	std::string searchPath = path;
> +	while (true) {
> +		searchPath += "/..";
> +		char *realPath = realpath(searchPath.c_str(), nullptr);
> +		if (!realPath) {
> +			LOG(UVC, Error) << "Failed to lookup " << searchPath;
> +			return {};
> +		}
> +		searchPath = realPath;
> +		free(realPath);
> +
> +		if (searchPath.empty() || searchPath == "/") {
> +			LOG(UVC, Error) << "Can not find controller ID";
> +			return {};
> +		}

As path is guaranteed to be a real path, I think this could be
simplified.

		std::string::size_type pos = searchPath.rfind('-');
		if (pos <= 1) {
			LOG(UVC, Error) << "Can not find controller ID";
			return {};
		}

		searchPath = searchPath::substr(0, pos);

> +
> +		if (!sysfs::firmwareId(searchPath, &controllerId))
> +			break;
> +	}
> +
> +	return controllerId + "-" + usbId + "-" + deviceId;
> +}
> +
>  bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
>  {
>  	MediaDevice *media;
> @@ -405,8 +474,14 @@ bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
>  		return false;
>  
>  	/* Create and register the camera. */
> +	std::string id = generateID(data.get());
> +	if (id.empty()) {
> +		LOG(UVC, Error) << "Failed to generate camera ID";
> +		return false;
> +	}
> +
>  	std::set<Stream *> streams{ &data->stream_ };
> -	std::shared_ptr<Camera> camera = Camera::create(this, media->model(), streams);
> +	std::shared_ptr<Camera> camera = Camera::create(this, id, streams);
>  	registerCamera(std::move(camera), std::move(data));
>  
>  	/* Enable hot-unplug notifications. */

-- 
Regards,

Laurent Pinchart