Adding Patch to an Application

In this section, you are going to learn

How to create patches ?

How to add patches to an application ?

How to add patches using diff and patch commands ?

How to add patches using quilt commands ?

Topics in this section,

Let us answer few basic questions

What is a patch ?

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.

What are the ways to generate and apply patch ?

See Answer

  • using diff and patch commands.

  • using quilt commands.

What is use of diff command ?

See Answer

  • command use to compare two files line by line.

What is use of patch command ?

See Answer

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

What is the command to generate patch file ?

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

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

See Answer
patch helloworld_org.c < add_patch_to_helloworld.diff

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

See Answer
patch -R helloworld_org.c < add_patch_to_helloworld.diff

What is quilt ?

See Answer

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

What quilt init does ?

See Answer

  • quilt init command is used to create a new quilt series.

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

What quilt new does ?

See Answer

  • quilt new is used to create a patch file.

* quilt new patch_file_name.patch

What quilt add does ?

See Answer

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

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

What quilt refresh does ?

See Answer

  • quilt refresh is used to update the series with latest modifications.

What quilt series does ?

See Answer

  • quilt series is used to display the name of the patches under that series.

What quilt push does ?

See Answer

  • quilt push is used to apply the patches.

What is quilt pop does ?

See Answer

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

What quilt top does ?

See Answer

  • quilt top is used to display the currently applied patch.

  • It displays the top most patch present in the series.

Let us now explore it in depth !

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

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

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.

patch <orginal_file_name> < <patch_file_name>

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

1#include <stdio.h>
2
3void main()
4{
5	printf("Hello-World\n");
6
7	return;
8}

  • Copy the file which needs to be modified to a new file and make the changes required.

1#include <stdio.h>
2
3void main()
4{
5	printf("Hello-World\n");
6	printf("Patch applied\n");
7	return;
8}

$ diff -u helloworld_orginal.c helloworld_modified.c > add_patch_to_helloworld.diff

 1--- helloworld_orginal.c	2024-01-02 12:10:14.076379091 +0530
 2+++ helloworld_modified.c	2024-01-02 12:10:41.905334438 +0530
 3 -3,6 +3,6 
 4 void main()
 5 {
 6 	printf("Hello-World\n");
 7-
 8+	printf("Patch applied\n");
 9 	return;
10 }

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

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

  • Step 1: create a new quilt series using quilt init command.

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

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

$ 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.

$ 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.

$ vi helloworld.c

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

$ quilt refresh
Refreshed patch patches/add_hello_world_patch.patch

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

1#include <stdio.h>
2
3int main(void)
4{
5	printf("Hello World\n");
6	return 0;
7}

 1SOURCE_FILE = helloworld.c
 2
 3all: apply_patches build
 4
 5apply_patches:
 6	quilt push || true  
 7
 8build:
 9	gcc $(SOURCE_FILE) -o helloworld
10
11clean: unapply_patches
12	rm -f helloworld
13
14unapply_patches:
15	quilt pop -a || true 
16
17.PHONY: all apply_patches build clean unapply_patches
18

$ 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

 1Index: app/helloworld.c
 2===================================================================
 3--- app.orig/helloworld.c
 4+++ app/helloworld.c
 5 int main(void)
 6 {
 7 	printf("Hello World\n");
 8+	printf("Patches Applied\n");
 9 	return 0;
10 }

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

Now at patch patches/add_hello_world_patch.patch

$ ./helloworld
Hello World
Patches Applied
See Also