> I would like to propose a third method, which may contain the best of
> both worlds (although it may also be hopelessly impractical):
>
> 1) Retain only 1 registration method (Gerd's fops method).
> 2) Remove all v4l1 compatibility into a separate module.
> 3) Have the compatibility module register distinct devices for v4l1
> compatibily.
I still don't like the separate devices for v4l1/2.
> 2) v4l2 drivers must do their own userspace copying (probably a single
> helper function in videodev that v4l2 modules must call).
Hmm, I think we don't have to do that way. The ioctl function (maybe
mmap too) in the compatibility module can be build in such a way that
a driver can hook these directly into his struct file_operations.
The ioctl function which does the real work (and no userspace copying)
can go into struct video_device. Like this:
int generic_video_ioctl(struct inode *inode, struct file *file,
unsigned int cmd, unsigned long arg)
{
// videodev.c must export the get_vfl() lookup function
struct video_device *vfl = get_vfl(inode);
// copy from userspace
err = vfl->kernel_ioctl(inode,file,cmd,copied_arg);
if (err == -ENOIOCTLCMD)
err = translate_ioctl(...)
// copy to userspace
return err;
}
Comes close to what videodevX.c does today. And we can easily split
videodev.c and the compatibility/helper code into multiple modules.
Gerd
