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    3. Device Communication and Control > Defining ioctl Commands

    Defining ioctl Commands

    To define an ioctl command, you’d call one of the following macros: _IO, _IOR, _IOW, or _IOWR. An explanation of each macro is provided in Table 3-1.

    Table 3-1. ioctl Command Macros

    Macro

    Description

    _IO

    Creates an ioctl command for an I/O operation that transfers no data—in other words, the data argument in d_ioctl will be unused—for example, ejecting removable media

    _IOR

    Creates an ioctl command for a read operation; read operations transfer data from the device to user space; for example, retrieving error information

    _IOW

    Creates an ioctl command for a write operation; write operations transfer data to the device from user space; for example, setting a device parameter

    _IOWR

    Creates an ioctl command for an I/O operation with bidirectional data transfers


      

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