Adding Patch to Kernel Module

In this section, you are going to learn

How to create patches ?

How to add patches to kernel module ?

How to add patches using diff and patch commands ?

How to add patches using quilt ?

Topics in this section,

• Adding Patch to Kernel Module : FAQs

• Adding Patch to Kernel Module : Creating Patches using diff and patch

• Adding Patch to Kernel Module : Adding Patches to Kernel Module using diff and patch

• Adding Patch to Kernel Module : Creating Patches using quilt

• Adding Patch to Kernel Module : Adding Patches to Kernel Module using quilt

Adding Patches to Application : FAQs

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 !

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.

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.

Adding Patches to kernel module using diff and patch

helloworld_original.c

#include <linux/init.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");

static int __init helloworld_init(void)
{
	printk(KERN_INFO "Hello world\n");

	return 0;
}

static void __exit helloworld_exit(void)
{
	printk(KERN_INFO "Exit\n");
}

module_init(helloworld_init);
module_exit(helloworld_exit);

helloworld_modified.c

#include <linux/init.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");

static int __init helloworld_init(void)
{
	printk(KERN_INFO "Hello world\n");
	printk(KERN_INFO "Patch added to kernel module\n");
	return 0;
}

static void __exit helloworld_exit(void)
{
	printk(KERN_INFO "Exit\n");
}

module_init(helloworld_init);
module_exit(helloworld_exit);

Makefile

obj-m += helloworld_original.o

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
	make -C /lib/modules/$(shell uname -r)/buld M=$(PWD) clean

Generating patch file using diff command

$ diff -u helloworld_original.c helloworld_modified.c < add_patch_to_kernel_mod.diff

Patching the source file using patch command

$ patch helloworld_original.c < add_patch_to_kernel_mod.diff
patching file helloworld_original.c

add_patch_to_kernel_mod.diff

--- helloworld_original.c	2024-01-02 16:42:13.460928842 +0530
+++ helloworld_modified.c	2024-01-02 16:43:11.604579126 +0530
 -6,7 +6,7 
 static int __init helloworld_init(void)
 {
 	printk(KERN_INFO "Hello world\n");
-
+	printk(KERN_INFO "Patch added to kernel module\n");
 	return 0;
 }
 

Compiling the kernel module

$ make

Executing the kernel module

$ sudo insmod ./helloworld_original.ko
$ sudo rmmmod helloworld_original
$ dmesg
[1233082.552450] Hello world
[1233082.552451] Patch added to kernel module
[1233093.272275] Exit

Creating Patches

• 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.

Adding Patches to Kernel Module

helloworld.c

#include <linux/init.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("Hello World Kernel Module");

static int __init hello_world_init(void) {
    printk(KERN_INFO "Hello World module loaded\n");
    return 0;
}

static void __exit hello_world_exit(void) {
    printk(KERN_INFO "Hello World module unloaded\n");
}

module_init(hello_world_init);
module_exit(hello_world_exit);

Makefile

obj-m += helloworld.o
KDIR := /lib/modules/$(shell uname -r)/build

QUILT_SERIES = my_patches
PATCHES_DIR = patches

all: apply_patches
	$(MAKE) -C $(KDIR) M=$(PWD) modules

apply_patches:
	quilt push || true

.PHONY: clean
clean:
	quilt pop -a || true
	$(MAKE) -C $(KDIR) M=$(PWD) clean

Adding patches to helloworld.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

add_kernel_module_patch.patch

Index: app/helloworld.c
===================================================================
--- app.orig/helloworld.c
+++ app/helloworld.c

 
 static int __init hello_world_init(void) {
     printk(KERN_INFO "Hello World!\n");
+    printk(KERN_INFO "patches applied to kernel module!\n");
     return 0;
 }
 

Compiling the application

$ make

Load the module into linux kernel

sudo insmod ./helloworld.ko

Checking for kernel buffer from the module

$ dmesg
[10472.955996] Hello World module loaded
[10955.989570] patches applied to kernel module!

Checking for module is loaded or not

$ lsmod | grep helloworld
helloworld             16384  0

Unloading module from linux kernel

$ sudo rmmod ./helloworld
$ dmesg
[10516.629413] Hello World module unloaded

See Also

• Other topics of linux x86

  • Adding Hello World Application

  • Adding Static Library

  • Adding Shared Library

  • Adding Hello World Kernel Module

  • Adding Patch to a Static Library

  • Adding Patch to a Shared Library

  • Adding Patch to an Application

• Current Module

  • Adding Patch to Kernel Module

• Previous Module

  • Adding Patch to a Shared Library

• Next Module

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