On Tue, Dec 6, 2011 at 10:41 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday 06 December 2011, Ming Lei wrote: >> > Using an array added to the end of the v4l2_fd_result structure >> > rather than a pointer would really make this easier IMHO. >> >> I have tried to do this, but video_usercopy needs a few changes >> to handle array args if no indirect pointer is passed to kernel. > > Ah, I see. Or you would have to encode the array size into the > ioctl command, which is also ugly in a different way. > >> I am not sure if media guys are happy to accept the changes, :-) > > Maybe Mauro can comment on which solution he prefers then, given > the choice between: > > 1. adding another handler in drivers/media/video/v4l2-compat-ioctl32.c > > 2. passing a pointer that is casted to __u64 in user space an back > in the kernel > > 3. extending video_usercopy in some way to make this work, preferably > in a generic way. Maybe this one is a good choice, and I think that it is worthy to support the below kind of array parameter: struct v4l2_fd_result { __u32 buf_index; __u32 face_cnt; __u32 reserved[6]; struct v4l2_fd_detection fd[]; }; and it is not difficult to implement it in a generic way so that new array parameters can be supported as 64/32 compatible. > 4. using a variable command number like > #define VIDIOC_G_FD_RESULT(num) _IOC(_IOC_READ|_IOC_WRITE,'V', 95, \ > sizeof(struct v4l2_fd_result) + (num) * sizeof(struct v4l2_fd_detection) > > 5. requiring the interface to be simplified to return only a single > struct v4l2_fd_detection at a time Maybe this one is not user friendly since other v4l2 interfaces provide array parameters way, :-) > I agree that none of these are nice. My preferred option would be last one, > but I don't know how performance critical the interface is or if it would > cause any races that you want to avoid. thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html