V4L2 ioctl() &manvol; v4l2-ioctl Program a V4L2 device #include <sys/ioctl.h> int ioctl int fd int request void *argp fd &fd; request V4L2 ioctl request code as defined in the videodev2.h header file, for example VIDIOC_QUERYCAP. argp Pointer to a function parameter, usually a structure. The ioctl() function is used to program V4L2 devices. The argument fd must be an open file descriptor. An ioctl request has encoded in it whether the argument is an input, output or read/write parameter, and the size of the argument argp in bytes. Macros and defines specifying V4L2 ioctl requests are located in the videodev2.h header file. Applications should use their own copy, not include the version in the kernel sources on the system they compile on. All V4L2 ioctl requests, their respective function and parameters are specified in . On success the ioctl() function returns 0 and does not reset the errno variable. On failure -1 is returned, when the ioctl takes an output or read/write parameter it remains unmodified, and the errno variable is set appropriately. See below for possible error codes. Generic errors like EBADF or EFAULT are not listed in the sections discussing individual ioctl requests. Note ioctls may return undefined error codes. Since errors may have side effects such as a driver reset applications should abort on unexpected errors. EBADF fd is not a valid open file descriptor. EBUSY The property cannot be changed right now. Typically this error code is returned when I/O is in progress or the driver supports multiple opens and another process locked the property. EFAULT argp references an inaccessible memory area. ENOTTY fd is not associated with a character special device. EINVAL The request or the data pointed to by argp is not valid. This is a very common error code, see the individual ioctl requests listed in for actual causes. ENOMEM Not enough physical or virtual memory was available to complete the request. ERANGE The application attempted to set a control with the &VIDIOC-S-CTRL; ioctl to a value which is out of bounds.