Re: [PATCH v2] V4L: dynamically allocate video_device nodes in subdevices

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

Hi Laurent

On Fri, 9 Sep 2011, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Friday 09 September 2011 19:45:57 Guennadi Liakhovetski wrote:
> > Currently only very few drivers actually use video_device nodes, embedded
> > in struct v4l2_subdev. Allocate these nodes dynamically for those drivers
> > to save memory for the rest.
> 
> Thanks for the patch.
> 
> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> > ---
> > 
> > v2: Checking for NULL is not always enough, you also have to check the
> > right thing for it. In this case it was sd->devnode in
> > v4l2_device_unregister_subdev().
> > 
> >  drivers/media/video/v4l2-device.c |   29 ++++++++++++++++++++++++++---
> >  include/media/v4l2-subdev.h       |   10 ++++++++--
> >  2 files changed, 34 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/media/video/v4l2-device.c
> > b/drivers/media/video/v4l2-device.c index c72856c..d4c093f 100644
> > --- a/drivers/media/video/v4l2-device.c
> > +++ b/drivers/media/video/v4l2-device.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/types.h>
> >  #include <linux/ioctl.h>
> >  #include <linux/i2c.h>
> > +#include <linux/slab.h>
> >  #if defined(CONFIG_SPI)
> >  #include <linux/spi/spi.h>
> >  #endif
> > @@ -194,6 +195,7 @@ EXPORT_SYMBOL_GPL(v4l2_device_register_subdev);
> >  int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
> >  {
> >  	struct video_device *vdev;
> > +	struct v4l2_devnode *node;
> >  	struct v4l2_subdev *sd;
> >  	int err;
> > 
> > @@ -204,7 +206,13 @@ int v4l2_device_register_subdev_nodes(struct
> > v4l2_device *v4l2_dev) if (!(sd->flags & V4L2_SUBDEV_FL_HAS_DEVNODE))
> >  			continue;
> > 
> > -		vdev = &sd->devnode;
> > +		node = kzalloc(sizeof(*node), GFP_KERNEL);
> > +		if (!node) {
> > +			err = -ENOMEM;
> > +			goto clean_up;
> > +		}
> > +		vdev = &node->vdev;
> > +
> >  		strlcpy(vdev->name, sd->name, sizeof(vdev->name));
> >  		vdev->v4l2_dev = v4l2_dev;
> >  		vdev->fops = &v4l2_subdev_fops;
> > @@ -213,13 +221,25 @@ int v4l2_device_register_subdev_nodes(struct
> > v4l2_device *v4l2_dev) err = __video_register_device(vdev,
> > VFL_TYPE_SUBDEV, -1, 1,
> >  					      sd->owner);
> >  		if (err < 0)
> > -			return err;
> > +			goto clean_up;
> >  #if defined(CONFIG_MEDIA_CONTROLLER)
> >  		sd->entity.v4l.major = VIDEO_MAJOR;
> >  		sd->entity.v4l.minor = vdev->minor;
> >  #endif
> > +		sd->devnode = node;
> >  	}
> >  	return 0;
> > +
> > +clean_up:
> > +	list_for_each_entry(sd, &v4l2_dev->subdevs, list) {
> > +		if (!sd->devnode)
> > +			break;
> > +		video_unregister_device(&sd->devnode->vdev);
> > +		kfree(sd->devnode);
> > +		sd->devnode = NULL;
> > +	}
> > +
> > +	return err;
> >  }
> >  EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
> > 
> > @@ -245,7 +265,10 @@ void v4l2_device_unregister_subdev(struct v4l2_subdev
> > *sd) if (v4l2_dev->mdev)
> >  		media_device_unregister_entity(&sd->entity);
> >  #endif
> > -	video_unregister_device(&sd->devnode);
> > +	if (sd->devnode)
> > +		video_unregister_device(&sd->devnode->vdev);
> > +	kfree(sd->devnode);
> 
> Won't this crash if the node is open ? I think you need to refcount it.

Hm, I've been thinking about it, but maybe not far enough.

> 
> > +	sd->devnode = NULL;
> >  	module_put(sd->owner);
> >  }
> >  EXPORT_SYMBOL_GPL(v4l2_device_unregister_subdev);
> > diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> > index 257da1a..6e958df 100644
> > --- a/include/media/v4l2-subdev.h
> > +++ b/include/media/v4l2-subdev.h
> > @@ -510,6 +510,12 @@ struct v4l2_subdev_internal_ops {
> >  /* Set this flag if this subdev generates events. */
> >  #define V4L2_SUBDEV_FL_HAS_EVENTS		(1U << 3)
> > 
> > +/* video_device with a reverse lookup */
> > +struct v4l2_devnode {
> > +	struct v4l2_subdev *sd;
> > +	struct video_device vdev;
> > +};
> > +
> 
> Instead of that, why don't you store the subdev pointer in the video_device 
> driver data ?

Is it free yet? Could do, sure.

> >  /* Each instance of a subdev driver should create this struct, either
> >     stand-alone or embedded in a larger struct.
> >   */
> > @@ -534,13 +540,13 @@ struct v4l2_subdev {
> >  	void *dev_priv;
> >  	void *host_priv;
> >  	/* subdev device node */
> > -	struct video_device devnode;
> > +	struct v4l2_devnode *devnode;
> >  };
> > 
> >  #define media_entity_to_v4l2_subdev(ent) \
> >  	container_of(ent, struct v4l2_subdev, entity)
> >  #define vdev_to_v4l2_subdev(vdev) \
> > -	container_of(vdev, struct v4l2_subdev, devnode)
> > +	(container_of(vdev, struct v4l2_devnode, vdev)->sd)
> > 
> >  /*
> >   * Used for storing subdev information per file handle

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/