ref: 2e05af858ec745ffc174e503148ef7928f697c22
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 *);