[libcamera-devel] [PATCH v3 5/5] libcamera: pipeline: Register device numbers with camera

[Kieran Bingham]

Quoting Laurent Pinchart (2023-06-06 17:27:36)
> Hi Kieran,
> 
> Thank you for the patch.
> 
> On Mon, May 15, 2023 at 01:45:50PM +0100, Kieran Bingham via libcamera-devel wrote:
> > Register the identified device numbers with each camera as the Devices
> > property.
> 
> Now that I read this, I wonder if we should call the property
> SystemDevices. It seems clearer to me but I'm not sure why :-)

man dev_t:

dev_t
Include: <sys/types.h>.  Alternatively, <sys/stat.h>.

Used for device IDs.  According to POSIX, it shall be an integer type.
For further details of this type, see makedev(3).

Conforming to: POSIX.1-2001 and later.

See also: mknod(2), stat(2)


or

man makedev:

NAME
       makedev, major, minor - manage a device number
DESCRIPTION

       A  device ID consists of two parts: a major ID, identifying the
       class of the device, and a minor ID, identifying a specific
       instance of a device in that class.  A device ID is represented
       using the type dev_t.

       Given major and minor device IDs, makedev() combines these to
       produce a device ID, returned as the function result.  This
       device ID can be given to mknod(2), for example.

       The major() and minor() functions perform the converse task:
       given a device ID, they return, respectively, the major and minor
       components.  These macros can be useful to,  for  example,
       decompose the device IDs in the structure returned by stat(2).

The value we store is only ever referenced as a 'device number'. They
help identify device nodes. They are part of the 'system' but then so
is everything else.

It may help if it clarifies these are 'internal (linux) system devices'
but what is a device in a linux system if it's not a system device?

IOW : If you want to ask for this to be SystemDevices, then that's fine.
- but it doesn't add anything to me..


> 
> > This facilitates camera daemons or other systems to identify which
> > devices are being managed by libcamera, and can prevent duplication of
> > camera resources.
> 
> Is it really duplication of resources, or resource usage conflicts ?


Well maybe it's both. It's means that resources are duplicated to the
user. They don't conflict unless they are both accessed at the same
time.




> > As the Devices property now provides this list of devices, use it
> > directly from within the CameraManager when adding a Camera rather than
> > passing it through the internal API.
> > 
> > Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> > ---
> >  include/libcamera/internal/camera_manager.h |  3 +--
> >  src/libcamera/camera_manager.cpp            | 14 +++++++++-----
> >  src/libcamera/pipeline_handler.cpp          | 12 ++++++++++--
> >  3 files changed, 20 insertions(+), 9 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/camera_manager.h b/include/libcamera/internal/camera_manager.h
> > index 885bb2825687..680e1f58cb02 100644
> > --- a/include/libcamera/internal/camera_manager.h
> > +++ b/include/libcamera/internal/camera_manager.h
> > @@ -29,8 +29,7 @@ public:
> >       Private();
> >  
> >       int start();
> > -     void addCamera(std::shared_ptr<Camera> camera,
> > -                    const std::vector<dev_t> &devnums) LIBCAMERA_TSA_EXCLUDES(mutex_);
> > +     void addCamera(std::shared_ptr<Camera> camera) LIBCAMERA_TSA_EXCLUDES(mutex_);
> >       void removeCamera(std::shared_ptr<Camera> camera) LIBCAMERA_TSA_EXCLUDES(mutex_);
> >  
> >       /*
> > diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
> > index 70eb4e455e54..7e499def9ddc 100644
> > --- a/src/libcamera/camera_manager.cpp
> > +++ b/src/libcamera/camera_manager.cpp
> > @@ -15,7 +15,9 @@
> >  #include <libcamera/base/utils.h>
> >  
> >  #include <libcamera/camera.h>
> > +#include <libcamera/property_ids.h>
> >  
> > +#include "libcamera/internal/camera.h"
> >  #include "libcamera/internal/device_enumerator.h"
> >  #include "libcamera/internal/pipeline_handler.h"
> >  
> > @@ -150,19 +152,17 @@ void CameraManager::Private::cleanup()
> >  /**
> >   * \brief Add a camera to the camera manager
> >   * \param[in] camera The camera to be added
> > - * \param[in] devnums The device numbers to associate with \a camera
> >   *
> >   * This function is called by pipeline handlers to register the cameras they
> >   * handle with the camera manager. Registered cameras are immediately made
> >   * available to the system.
> >   *
> > - * \a devnums are used by the V4L2 compatibility layer to map V4L2 device nodes
> > - * to Camera instances.
> > + * Device numbers from the Devices property are used by the V4L2 compatibility
> > + * layer to map V4L2 device nodes to Camera instances.
> >   *
> >   * \context This function shall be called from the CameraManager thread.
> >   */
> > -void CameraManager::Private::addCamera(std::shared_ptr<Camera> camera,
> > -                                    const std::vector<dev_t> &devnums)
> > +void CameraManager::Private::addCamera(std::shared_ptr<Camera> camera)
> >  {
> >       ASSERT(Thread::current() == this);
> >  
> > @@ -177,6 +177,10 @@ void CameraManager::Private::addCamera(std::shared_ptr<Camera> camera,
> >               }
> >       }
> >  
> > +     auto devnums = camera->properties()
> > +                            .get(properties::Devices)
> > +                            .value_or(Span<int64_t>{});
> > +
> >       cameras_.push_back(std::move(camera));
> >  
> >       unsigned int index = cameras_.size() - 1;
> > diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
> > index 49092ea88a58..0b5fac7ad113 100644
> > --- a/src/libcamera/pipeline_handler.cpp
> > +++ b/src/libcamera/pipeline_handler.cpp
> > @@ -17,6 +17,7 @@
> >  
> >  #include <libcamera/camera.h>
> >  #include <libcamera/framebuffer.h>
> > +#include <libcamera/property_ids.h>
> >  
> >  #include "libcamera/internal/camera.h"
> >  #include "libcamera/internal/camera_manager.h"
> > @@ -612,7 +613,7 @@ void PipelineHandler::registerCamera(std::shared_ptr<Camera> camera)
> >        * Walk the entity list and map the devnums of all capture video nodes
> >        * to the camera.
> >        */
> > -     std::vector<dev_t> devnums;
> > +     std::vector<int64_t> devnums;
> >       for (const std::shared_ptr<MediaDevice> &media : mediaDevices_) {
> >               for (const MediaEntity *entity : media->entities()) {
> >                       if (entity->pads().size() == 1 &&
> > @@ -624,7 +625,14 @@ void PipelineHandler::registerCamera(std::shared_ptr<Camera> camera)
> >               }
> >       }
> >  
> > -     manager_->_d()->addCamera(std::move(camera), devnums);
> > +     /*
> > +      * Store the associated devices as a property of the camera to allow
> > +      * systems to identify which devices are managed by libcamera.
> > +      */
> > +     Camera::Private *data = camera->_d();
> > +     data->properties_.set(properties::Devices, devnums);
> > +
> > +     manager_->_d()->addCamera(std::move(camera));
> >  }
> >  
> >  /**
> 
> -- 
> Regards,
> 
> Laurent Pinchart