ref: eb4bd4aa3ec7308fd4dea9810c7d2de1f5977288
dir: /sys/src/cmd/nusb/cam/fns.h/
char *ctlread(Cam *); void printDescriptor(Fmt *, Iface *, void *); int videoopen(Cam *, int); void videoclose(Cam *); void videoread(Req *, Cam *, int); void videoflush(Req *, Cam *); int getframedesc(Cam *, int, int, Format **, VSUncompressedFrame **); int ctlwrite(Cam *, char *);