Adding Patch to an Application
=================================

In this section, you are going to learn

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	How to create patches ?

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	How to add patches to an application ?

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	How to add patches using diff and patch commands ?

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        How to add patches using quilt commands ? 

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	Topics in this section,

		* :ref:`Adding Patch to an Application : FAQs <linux_x86_c_add_app_patch_0_1>`
                * :ref:`Adding Patch to an Application : Creating Patches using diff and patch <linux_x86_c_add_app_patch_0_2>`
                * :ref:`Adding Patch to an Application : Adding Patches to an Application using diff and patch <linux_x86_c_add_app_patch_0_3>`
                * :ref:`Adding Patch to an Application : Creating Patches using quilt <linux_x86_c_add_app_patch_0_4>`
		* :ref:`Adding Patch to an Application : Adding Patches to an Application using quilt <linux_x86_c_add_app_patch_0_5>`

.. _linux_x86_c_add_app_patch_0_1:

.. tab-set::

        .. tab-item:: Adding Patches to Application : FAQs

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			Let us answer few basic questions

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			What is a patch ?

			.. dropdown:: See Answer

                                * It is a file or set of changes made to a source code of program to modify or update it.
                                * Used to fix bugs or add new features to existing ones.
                        
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                        What are the ways to generate and apply patch ?

                        .. dropdown:: See Answer

                                * using diff and patch commands.
                                * using quilt commands.
              
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                        What is use of diff command ?

                        .. dropdown:: See Answer

                                * command use to compare two files line by line.

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                        What is use of patch command ?

                        .. dropdown:: See Answer

                                * applies changes to the source code by reading the diff file.                                                       

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                        What is the command to generate patch file ?

                        .. dropdown:: See Answer
                
                                .. code-block:: c

                                        diff -u helloworld_org.c helloworld.c > add_patch_to_helloworld.diff

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                        What is the command to apply the patches to source code ?

                        .. dropdown:: See Answer

                                .. code-block:: c

                                        patch helloworld_org.c < add_patch_to_helloworld.diff

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                        What is the command to remove the patches from source code ?

                        .. dropdown:: See Answer
                  
                                .. code-block:: c 
                                
                                        patch -R helloworld_org.c < add_patch_to_helloworld.diff

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			What is quilt ?

			.. dropdown:: See Answer

                                * Tools used for managing a series of patches applied to the source code repository.

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			What quilt init does ?

			.. dropdown:: See Answer
       
                                * quilt init command is used to create a new quilt series.

                                .. code-block:: c

                                        $ quilt init
                                        The quilt meta-data is now initialized.


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			What quilt new does ?

			.. dropdown:: See Answer

                                * quilt new is used to create a patch file.

                                .. code-block:: c

                                        * quilt new patch_file_name.patch

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                        What quilt add does ?

			.. dropdown:: See Answer

                                * quilt add is used to add the source code files which needs to be modified.

                                .. code-block :: c

                                        quilt add <file1> <file2> ..... <fileN>

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                        What quilt refresh does ?

			.. dropdown:: See Answer
                               
                                * quilt refresh is used to update the series with latest modifications.


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                        What quilt series does ?

                        .. dropdown:: See Answer
                               
                                * quilt series is used to display the name of the patches under that series.

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                        What quilt push does ?

                        .. dropdown:: See Answer

                                * quilt push is used to apply the patches.

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                        What is quilt pop does ?

                        .. dropdown:: See Answer

                                * quilt pop is used to unapply the top most patch in the series.

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                        What quilt top does ?

                        .. dropdown:: See Answer

                                * quilt top is used to display the currently applied patch.
                                * It displays the top most patch present in the series.

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			Let us now explore it in depth !

.. _linux_x86_c_add_app_patch_0_2:

.. tab-set::

        .. tab-item:: Creating Patches using diff and patch

                * Step 1: Edit the file which needs to be modified.

                * Step 2: Generate a patch file using the diff command.

                .. code-block:: c

                        diff -u <original_file_name> <modified_file_name> > <patch_file_name>

                * Step 3: Now the patches to the file can be applied using patch command.

                .. code-block:: c

                        patch <orginal_file_name> < <patch_file_name>

                * Now a patch is created and the changes is applied to the file.

.. _linux_x86_c_add_app_patch_0_3:

.. tab-set::

        .. tab-item:: Adding patches to an Application using diff and patch

                .. tab-set::

                        .. tab-item:: helloworld_orginal.c
        
                                .. literalinclude:: app_diff/helloworld_original.c
                                        :language: c
                                        :linenos:

                .. tab-set::

                        .. tab-item:: helloworld_modified.c

                                 * Copy the file which needs to be modified to a new file and make the changes required.
                        
                                .. literalinclude:: app_diff/helloworld_modified.c
                                        :language: c
                                        :linenos:

                .. tab-set::

                        .. tab-item:: Generating patch file using diff command.

                                .. code-block:: c

                                        $ diff -u helloworld_orginal.c helloworld_modified.c > add_patch_to_helloworld.diff
                                
                                .. tab-set::
        
                                        .. tab-item:: add_patch_to_helloworld.diff
                                        
                                                .. literalinclude:: app_diff/add_patch_to_helloworld.diff
                                                        :language: c
                                                        :linenos:

               .. tab-set::

                        .. tab-item:: Applying patches to the source code using patch command

                                .. code-block:: c

                                        $ patch helloworld_orginal.c < add_patch_to_helloworld.diff 
                                        patching file helloworld_orginal.c

               .. tab-set::

                        .. tab-item:: Compiling and Executing the Application

                                .. code-block:: c

                                        $ gcc helloworld_orginal.c 
                                        $ ./a.out 
                                        Hello-World
                                        Patch applied

.. _linux_x86_c_add_app_patch_0_4:

.. tab-set::

        .. tab-item:: Creating Patches using quilt
                
                
                * Step 1: create a new quilt series using quilt init command.

                .. code-block:: c

                        $ quilt init
                        The quilt meta-data is now initialized.

                * Step 2: create a patch file using quilt new command.

                .. code-block :: c

                        $ quilt new add_hello_world_patch.patch
                        Patch patches/add_hello_world_patch.patch is now on top


                * Step 3: add the file which needs to be modified using quilt add command.

                .. code-block :: c

                        $ quilt add helloworld.c 
                        File helloworld.c added to patch patches/add_hello_world_patch.patch

                * Step 4: edit the file and make the modifications needed.

                .. code-block :: c

                        $ vi helloworld.c

                * Step 5: once the changes is added run quilt refresh to update the series with latest modifications.

                .. code-block :: c

                        $ quilt refresh
                        Refreshed patch patches/add_hello_world_patch.patch

                * Now a patch is created and changes has been added to the series.


.. _linux_x86_c_add_app_patch_0_5:

.. tab-set::

        .. tab-item:: Adding Patches to an Application using quilt
                
                .. tab-set::
                        
                        .. tab-item:: helloworld.c

                                .. literalinclude:: app/helloworld.c
                                        :language: c
                                        :linenos: 

                .. tab-set::

                        .. tab-item:: Makefile

                                .. literalinclude:: app/Makefile
                                        :language: c
                                        :linenos:

                .. tab-set::

                        .. tab-item:: Adding patches to helloworld.c

                                .. code-block :: c

                                        $ quilt init
                                        The quilt meta-data is now initialized.
                                        $ quilt new add_hello_world_patch.patch
                                        Patch patches/add_hello_world_patch.patch is now on top
                                        $ quilt add helloworld.c 
                                        File helloworld.c added to patch patches/add_hello_world_patch.patch
                                        $ vi helloworld.c 
                                        $ quilt refresh
                                        Refreshed patch patches/add_hello_world_patch.patch
               

                                .. tab-set::

                                        .. tab-item:: add_hello_world_patch.patch

                                                .. literalinclude:: app/patches/add_hello_world_patch.patch
                                                        :language: c
                                                        :linenos:
                .. tab-set::

                        .. tab-item:: Compiling the application

                                .. code-block:: c

                                        $ make
                                        Applying patch patches/add_hello_world_patch.patch
                                        patching file helloworld.c

                                        Now at patch patches/add_hello_world_patch.patch
             
                .. tab-set::

                        .. tab-item:: Executing the application

                                .. code-block:: c

                                        $ ./helloworld 
                                        Hello World
                                        Patches Applied

.. card:: See Also

	* Other topics of linux x86

		* :doc:`../add_hello_world_app/add_hello_world_app`
		* :doc:`../add_static_lib/add_static_lib`
		* :doc:`../add_shared_lib/add_shared_lib`
		* :doc:`../add_hello_world_kernel_mod/add_hello_world_kernel_mod`
		* :doc:`../add_static_lib_patch/add_static_lib_patch`
		* :doc:`../add_shared_lib_patch/add_shared_lib_patch`
		* :doc:`../add_kernel_mod_patch/add_kernel_mod_patch`

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                * :doc:`../add_application_patch/add_application_patch`

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