The ioctl() function 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 request argument and an optional third argument with varying type are passed to the file designated by fildes and are interpreted by the device driver.
For STREAMS files, specific functions are performed by the ioctl() function as described in streamio(7I).
The fildes argument is an open file descriptor that refers to a device. The request argument selects the control function to be performed and depends
on the device being addressed. The arg argument represents a third argument that has 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 int 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(7I)).
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