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User Extra Character Device
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Overview
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The QDMA Linux driver provides an extensible character device interface that lets you add your own additional ``open``, ``close``, and ``ioctl`` handlers without changing the core driver. By default these handlers are ``NULL``; register your own in ``user_extra.c`` to add custom behavior.

**Prerequisites:**

For detailed driver configuration and application usage, refer to the `QDMA Linux driver build and usage guide <https://xilinx.github.io/dma_ip_drivers/master/QDMA/linux-kernel/html/build.html>`_.


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Building and Usage Steps
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Step#1: Implement Custom Callbacks
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Add your custom function callbacks in the user_extra.c file.

**File Location:**

drivers/linux/driver/user_extra/user_extra.c

**Callback Structure:**

Modify the `extra_cb` structure with your custom handlers:

::

   static const struct user_extra_cdev_cb extra_cb = {
       .open =  your_custom_open_function,   /* Replace NULL with your open method */
       .close = your_custom_close_function,  /* Replace NULL with your close method */
       .ioctl = your_custom_ioctl_function,  /* Replace NULL with your ioctl method */
   };

Note: By default, all callbacks are set to NULL. Users must assign their callback functions in this file based on their specific use case.

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Step#2: Build the Driver
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Compile the driver with USER_EXTRA_SUPPORTED flag:

::

   $> make USER_EXTRA_SUPPORTED=1

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Step#3: Install and Load
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Install and load the driver module:

::

   $> make install
   $> modprobe qdma-pf