ioctl(S)                       6 January 1993                       ioctl(S)


 Name

    ioctl - I/O control command

 Syntax


    cc ... -lc


    int ioctl (fildes, request, arg)
    int fildes, request;


 Description

    The ioctl system call performs a variety of control functions on devices
    and STREAMS.  For non-STREAMS files, the functions performed by this call
    are device-specific control functions.  The arguments request and arg are
    passed to the file designated by fildes and are interpreted by the device
    driver.  Basic input/output functions in STREAMS are performed with the
    read(S) and write(S) system calls.

    fildes is an open file descriptor that refers to a device.  request
    selects the control function to be performed and depends on the device
    being addressed.  arg represents additional information that is needed by
    this specific device to perform the requested function.  The data type of
    arg depends upon the particular control request, but it is either an
    integer or a pointer to a device-specific data structure.

    In addition to device-specific and STREAMS functions, generic functions
    are provided by more than one device driver, for example, the general
    terminal interface (see termio(M)).

    The ioctl system call fails for any type of file if one or more of the
    following is true:

    [EACCES]  Future error.

    [EBADF]   fildes is not a valid open file descriptor.

    [EINTR]   A signal was caught during the ioctl system call.

    [ENOTTY]  fildes is not associated with a device driver that accepts con-
              trol functions.

    The ioctl system call also fails if the device driver detects an error.
    In this case, the error is passed through ioctl without change to the
    caller.  A particular driver might not have all of the following error
    cases.  Other requests to device drivers fails if one or more of the fol-
    lowing is true:

    [EFAUL]    request requires a data transfer to or from a buffer pointed
               to by arg, but some part of the buffer is outside the pro-
               cess's allocated space.

    [EINVAL]   request or arg is not valid for this device.

    [EIO]      Some physical I/O error has occurred.

    [ENOLINK]  fildes is on a remote machine and the link to that machine is
               no longer active.

    [ENXIO]    The request and arg are valid for this device driver, but the
               service requested cannot be performed on this particular
               subdevice.

    STREAMS errors are described in streamio(STR).

 Diagnostics

    Upon successful completion, the value returned depends upon the device
    control function, but must be a non-negative integer. Otherwise, a value
    of -1 is returned, and errno is set to indicate the error.

 See also

    termio(M)

 Standards conformance

    ioctl is conformant with:
    AT&T SVID Issue 2;
    and Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2).