Tasklet Enable
==============

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    Topics in this section,

        * :ref:`Version Info <p1_taskletstatic_0>`

        * :ref:`Learnings in this section <p1_taskletstatic_1>`

        * :ref:`Explanation of tasklet APIs <p1_taskletstatic_2>`

                * :ref:`tasklet_init <p1_taskletstatic_3>`

                * :ref:`tasklet_disable <p1_taskletstatic_4>`
                
                * :ref:`tasklet_enable <p1_taskletstatic_22>`

                * :ref:`tasklet_schedule <p1_taskletstatic_23>`

                * :ref:`tasklet_kill <p1_taskletstatic_5>`

        * :ref:`Explanation of miscellaneous APIs <p1_taskletstatic_6>`

                * :ref:`Module parameter APIs <p1_taskletstatic_7>`

                * :ref:`Driver entry point APIs <p1_taskletstatic_8>`

        * :ref:`Example 1: Scheduling the periodic tasklet using tasklet_hi_schedule <p1_taskletstatic_9>`

                * :ref:`List of headers <p1_taskletstatic_10>`

                * :ref:`Module Macros <p1_taskletstatic_11>`
              
                * :ref:`Declare and Initialize tasklet <p1_taskletstatic_12>`

                * :ref:`Tasklet Handler Function <p1_taskletstatic_13>`

                * :ref:`Tasklet Start Function <p1_taskletstatic_14>`

                * :ref:`Task Init Function <p1_taskletstatic_15>`

                * :ref:`Tasklet Stop Function <p1_taskletstatic_16>`

                * :ref:`Task Exit Function <p1_taskletstatic_17>`
            
                * :ref:`Driver entry points <p1_taskletstatic_18>`

                * :ref:`See the full program below <p1_taskletstatic_19>`
            
                * :ref:`Makefile <p1_taskletstatic_20>`
            
                * :ref:`Compile and load the module <p1_taskletstatic_21>`


.. _p1_taskletstatic_0:
 
.. tab-set::
 
    .. tab-item:: Version Info

        =============================== =======================================
        #                               Version
        =============================== =======================================
        Ubuntu                          Ubuntu 22.10
        Kernel                          6.8.0
        =============================== =======================================


.. _p1_taskletstatic_1:

.. tab-set::

    .. tab-item:: Learnings in this section

        * In this program, you are going to learn

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                * How to create tasklet ?

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                * What are the different ways to create tasklet ?

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                * How to enable the tasklet ?

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                * How to disable the tasklet ?

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                * How to schedule the tasklet ?

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                * How to kill the tasklet ?

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                * How to use tasklet APIs ?

                        * `tasklet_init <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L750>`_

                        * `tasklet_disable <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L736>`_

                        * `tasklet_enable <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L743>`_

                        * `tasklet_schedule <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L705>`_

                        * `tasklet_kill <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L749>`_

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                * How to use below APIs ?

                        * `MODULE_LICENSE <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L230>`_

                        * `MODULE_DESCRIPTION <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L239>`_

                        * `MODULE_AUTHOR <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L236>`_

                        * `module_init <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L88>`_

                        * `module_exit <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L100>`_

.. _p1_taskletstatic_2:

.. tab-set::

    .. tab-item:: Explanation of tasklet APIs

        .. _p1_taskletstatic_3:

        .. tab-set::

            .. tab-item:: asklet_init

                * Here is the function prototype of the API: `tasklet_init <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L750>`_

                .. code-block:: c

                        #include <linux/interrupt.h>

                        extern void tasklet_init(struct tasklet_struct *t, void (*func)(unsigned long), unsigned long data);

                * Here is an example of how to use the API,

                .. code-block:: c

                        tasklet_init(my_tasklet, tasklet_handler, 10);

        .. _p1_taskletstatic_4:

        .. tab-set::

            .. tab-item:: tasklet_disable

                * Here is the function prototype of the API: `tasklet_disable <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L736>`_

                .. code-block:: c

                        #include <linux/interrupt.h>
                        
                        static inline void tasklet_disable(struct tasklet_struct *t);

                * Here is an example of how to use the API,

                .. code-block:: c

                        tasklet_disable(my_tasklet);

        .. _p1_taskletstatic_22:

        .. tab-set::

            .. tab-item:: tasklet_enable

                * Here is the function prototype of the API: `tasklet_enable <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L743>`_

                .. code-block:: c

                        #include <linux/interrupt.h>
                        
                        static inline void tasklet_enable(struct tasklet_struct *t);

                * Here is an example of how to use the API,

                .. code-block:: c

                        tasklet_enable(my_tasklet);

        .. _p1_taskletstatic_23:

        .. tab-set::

            .. tab-item:: tasklet_schedule

                * Here is the function prototype of the API: `tasklet_schedule <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L705>`_

                .. code-block:: c

                        #include <linux/interrupt.h>
                        
                        static inline void tasklet_schedule(struct tasklet_struct *t);
                        
                * Here is an example of how to use the API,

                .. code-block:: c

                        tasklet_schedule(my_tasklet);

        .. _p1_taskletstatic_5:

        .. tab-set::

            .. tab-item:: tasklet_kill

                * Here is the function prototype of the API: `tasklet_kill <https://elixir.bootlin.com/linux/v6.2/source/include/linux/interrupt.h#L749>`_

                .. code-block:: c

                        #include <linux/interrupt.h>

                        extern void tasklet_kill(struct tasklet_struct *t);
                        
                * Here is an example of how to use the API,

                .. code-block:: c

                        tasklet_kill(&my_tasklet);

.. _p1_taskletstatic_6:

.. tab-set::

    .. tab-item:: Explanation of miscellaneous APIs

        .. _p1_taskletstatic_7:

        .. tab-set::

            .. tab-item:: Module parameter APIs

                * Here is the prototype of module paramter APIs

                .. code-block:: c

                    #include <linux/module.h>

                    #define MODULE_LICENSE(_license) MODULE_FILE MODULE_INFO(license, _license)
                    #define MODULE_AUTHOR(_author) MODULE_INFO(author, _author)
                    #define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)


                * where

                    * `MODULE_LICENSE <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L230>`_: tells the kernel what license is used by our module.

                    * `MODULE_AUTHOR <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L236>`_: denotes the author of this kernel module.

                    * `MODULE_DESCRIPTION <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L239>`_: gives a basic idea about what the kernel module does.

                    * These information can be found when modinfo command is used which lists out all these above mentioned information.


                * Here is the example of how to use the Module parameter APIs,

                .. code-block:: c

                        MODULE_LICENSE("GPL");
                        MODULE_AUTHOR("usr");
                        MODULE_DESCRIPTION("Tasklet");

        .. _p1_taskletstatic_8:

        .. tab-set::

            .. tab-item:: Driver entry point API's

                * Here is the prototype of the Driver entry point API's

                .. code-block:: c

                    #include <linux/module.h>

                    #define module_init(x)      __initcall(x);
                    #define module_exit(x)      __exitcall(x);

                * where

                    * `module_init <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L88>`_: driver initialization entry point which will be called at module insertion time.

                    * `module_exit <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L100>`_: driver exit entry point which will be called during the removal of module.

                    * x:    
                            * function to be run at module insertion for `module_init <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L88>`_ function.
                            * function to be run when driver is removed for `module_exit <https://elixir.bootlin.com/linux/v6.7.9/source/include/linux/module.h#L100>`_ function.

                * Here is an example of how to use the driver entry point API's

                .. code-block:: c

                        module_init(task_init);
                        module_exit(task_exit);

.. _p1_taskletstatic_9:

.. tab-set::

    .. tab-item:: Example 1: Enabling the tasklet using tasklet_enable

        * In this example let’s see how to enable the tasklet and execute it.

        .. _p1_taskletstatic_10:

        .. tab-set::

            .. tab-item:: List of headers

                * Include the follow header files(.h) to refer the API being used for the execution.

                .. code-block:: c

                        #include <linux/init.h>
                        #include <linux/kernel.h>
                        #include <linux/module.h>
                        #include <linux/fs.h>
                        #include <linux/interrupt.h> 

        .. _p1_taskletstatic_11:

        .. tab-set::

            .. tab-item:: Module macros

                * Add the following module macros to display information about the license, author and description about the module.

                .. code-block:: c

                        MODULE_LICENSE("GPL");
                        MODULE_AUTHOR("usr");
                        MODULE_DESCRIPTION("Tasklet");

        .. _p1_taskletstatic_12:

        .. tab-set::

            .. tab-item:: Initialize the tasklet dynamically.

                * Initialize the tasklet which we are going to create and use in this example

                .. code-block:: c

                        tasklet_init(my_tasklet, tasklet_handler, 10);

        .. _p1_taskletstatic_13:

        .. tab-set::

            .. tab-item:: Tasklet Handler Function

                * This function executes once the tasklet is scheduled using tasklet_schedule.

                .. code-block:: c

                        void tasklet_handler(unsigned long data)
                        {
                                pr_info("Inside tasklet handler function\n");
                                pr_info("data : %ld\n", data);
                        }

        .. _p1_taskletstatic_14:

        .. tab-set::

            .. tab-item:: Tasklet Start Function

                * This function initializes the tasklet dynamically using tasklet_init.

                * Disabling the tasklet using tasklet_disable.

                * Enabling the tasklet using tasklet_enable.

                * Scheduling a tasklet using tasklet_schedule

                .. code-block:: c

                        void tasklet_start(void)
                        {
                                my_tasklet = kmalloc(sizeof(struct tasklet_struct), GFP_KERNEL);
                                if (my_tasklet == NULL)
                                        pr_info("Cannot allocate memory\n");
                                tasklet_init(my_tasklet, tasklet_handler, 10);
                                tasklet_disable(my_tasklet);
                                pr_info("tasklet disabled!!\n");

                                tasklet_enable(my_tasklet);
                                pr_info("tasklet enabled!!\n");
                                pr_info("Scheduling the tasklet\n");
                                tasklet_schedule(my_tasklet);
                        }
                         
        .. _p1_taskletstatic_15:

        .. tab-set::

            .. tab-item:: Task Init Function

                * This function calls tasklet_start function, will be executed once the module is loaded into the linux kernel.

                .. code-block:: c

                        static int __init task_init(void)
                        {
                                pr_info("driver loaded\n");
                                tasklet_start();
                                return 0;
                        }

        .. _p1_taskletstatic_16:

        .. tab-set::

            .. tab-item:: Tasklet Stop Function

                * This function kills tasklet and stops it's execution.

                .. code-block:: c

                        void tasklet_stop(void)
                        {
                                tasklet_kill(my_tasklet);
                                if (my_tasklet != NULL)
                                        kfree(my_tasklet);
                        }

        .. _p1_taskletstatic_17:

        .. tab-set::

            .. tab-item:: Task Exit Function

                * This function calls tasklet_stop function, will be executed once the module is removed from the linux kernel

                .. code-block:: c
                
                        static void __exit task_exit(void)
                        {
                                pr_info("driver unloaded!\n");
                                tasklet_stop();
                        }

        .. _p1_taskletstatic_18:

        .. tab-set::

            .. tab-item:: Driver entry points

                * Add the driver entry points which will be executed once the module is inserted or removed from the kernel.

                .. code-block:: c
    
                        module_init(task_init);
                        module_exit(task_exit);

        .. _p1_taskletstatic_19:

        .. tab-set::

            .. tab-item:: See the full program below

                .. tab-set::
                    
                    .. tab-item:: tasklet.c

                       .. literalinclude:: enable_tasklet/tc1/tasklet.c 
                            :language: c
                            :linenos:

        .. _p1_taskletstatic_20:

        .. tab-set::

            .. tab-item:: Makefile

                .. literalinclude:: enable_tasklet/tc1/Makefile
                    :language: c
                    :linenos:

        .. _p1_taskletstatic_21:

        .. tab-set::

            .. tab-item:: Compile and load the module

                * Run make to compile the kernel source and generate the .ko image.

                .. code-block:: shell

                        $ make
			make -C /lib/modules/6.8.0/build M=/home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1 modules
			make[1]: Entering directory '/home/arun/Desktop/kernel_api/linux-6.8'
			  CC [M]  /home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1/tasklet.o
			  MODPOST /home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1/Module.symvers
			  CC [M]  /home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1/tasklet.mod.o
			  LD [M]  /home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1/tasklet.ko
			make[1]: Leaving directory '/home/arun/Desktop/kernel_api/linux-6.8'

                * Check if the .ko is generated or not using ls command.

                .. code-block:: shell

                        $ ls -l
			total 384
			-rw-rw-r-- 1 arun arun    206 Jun 24 18:08 Makefile
			-rw-rw-r-- 1 arun arun     67 Jul 11 18:07 modules.order
			-rw-rw-r-- 1 arun arun      0 Jul 11 18:07 Module.symvers
			-rw-rw-r-- 1 arun arun   1739 Jun 24 18:21 tasklet.c
			-rw-rw-r-- 1 arun arun 183984 Jul 11 18:07 tasklet.ko
			-rw-rw-r-- 1 arun arun     67 Jul 11 18:07 tasklet.mod
			-rw-rw-r-- 1 arun arun   1206 Jul 11 18:07 tasklet.mod.c
			-rw-rw-r-- 1 arun arun 149480 Jul 11 18:07 tasklet.mod.o
			-rw-rw-r-- 1 arun arun  35896 Jul 11 18:07 tasklet.o

                * Run modinfo command to get the information about the kernel module.
 
                .. code-block:: shell
 
                        $ modinfo tasklet.ko
			filename:       /home/arun/Desktop/kernel_api/tasklet/enable_tasklet/tc1/tasklet.ko
			description:    Tasklet
			author:         usr
			license:        GPL
			srcversion:     95F2E664FF490892B1A8510
			depends:        
			retpoline:      Y
			name:           tasklet
			vermagic:       6.8.0 SMP preempt mod_unload modversions 

                * insert the module using insmod command.

                .. code-block:: shell

                        $ sudo insmod ./tasklet.ko 

                * check if the module is loaded or not using lsmod command.

                .. code-block:: shell

                        $ lsmod | grep tasklet
                        tasklet                12288  0

                * check for the kernel messages from init function and thread function once the module is loaded and thread is created.

                .. code-block:: shell

                        $ sudo dmesg 
                        [541232.695047] driver loaded
			[541232.695057] tasklet disabled!!
			[541232.695059] tasklet enabled!!
			[541232.695061] Scheduling the tasklet
			[541232.695622] Inside tasklet handler function
			[541232.695627] data : 10

                * remove the module from kernel using rmmod command.

                .. code-block:: shell

                        $ sudo rmmod tasklet

                * check if the module is still loaded after removing the kernel module using lsmod if it is not displayed in lsmod output it is verified that the module is removed successfully.

                .. code-block:: shell

                        $ lsmod | grep tasklet

                * Check for kernel messages from exit function using dmesg command.

                .. code-block:: shell

                        $ sudo dmesg 
			[534946.455200] driver unloaded