This is the latest (main) BeagleBoard documentation. If you are looking for stable releases, use the drop-down menu on the bottom-left and select the desired version.

The Kernel

The kernel is the heart of the Linux operating system. It’s the software that takes the low-level requests, such as reading or writing files, or reading and writing general-purpose input/output (GPIO) pins, and maps them to the hardware. When you install a new version of the OS (Verifying You Have the Latest Version of the OS on Your Bone), you get a certain version of the kernel.

You usually won’t need to mess with the kernel, but sometimes you might want to try something new that requires a different kernel. This chapter shows how to switch kernels. The nice thing is you can have multiple kernels on your system at the same time and select from among them which to boot up.

Updating the Kernel

Problem

You have an out-of-date kernel and want to make it current.

Solution

Use the following command to determine which kernel you are running:

bone$ uname -a
Linux beaglebone 5.10.168-ti-r62 #1bullseye SMP PREEMPT Tue May 23 20:15:00 UTC 2023 armv7l GNU/Linux
GNU/Linux

The 5.10.168-ti-r62 string is the kernel version.

To update to the current kernel, ensure that your Bone is on the Internet (Sharing the Host’s Internet Connection over USB or Establishing an Ethernet-Based Internet Connection) and then run the following commands:

bone$ apt-cache pkgnames | grep linux-image | sort | less
...
linux-image-5.10.162-ti-r59
linux-image-5.10.162-ti-rt-r56
linux-image-5.10.162-ti-rt-r57
linux-image-5.10.162-ti-rt-r58
linux-image-5.10.162-ti-rt-r59
linux-image-5.10.168-armv7-lpae-x71
linux-image-5.10.168-armv7-rt-x71
linux-image-5.10.168-armv7-x71
linux-image-5.10.168-bone71
linux-image-5.10.168-bone-rt-r71
linux-image-5.10.168-ti-r60
linux-image-5.10.168-ti-r61
linux-image-5.10.168-ti-r62
linux-image-5.10.168-ti-rt-r60
linux-image-5.10.168-ti-rt-r61
linux-image-5.10.168-ti-rt-r62
...

bone$ sudo apt install linux-image-5.10.162-ti-rt-r59
bone$ sudo reboot

bone$ uname -a
Linux beaglebone 5.10.162-ti-rt-r59 #1 SMP PREEMPT Wed Nov 19 21:11:08 UTC 2014 armv7l
GNU/Linux

The first command lists the versions of the kernel that are available. The second command installs one. After you have rebooted, the new kernel will be running.

If the current kernel is doing its job adequately, you probably don’t need to update, but sometimes a new software package requires a more up-to-date kernel. Fortunately, precompiled kernels are available and ready to download.

Building and Installing Kernel Modules

Problem

You need to use a peripheral for which there currently is no driver, or you need to improve the performance of an interface previously handled in user space.

Solution

The solution is to run in kernel space by building a kernel module. There are entire books on writing Linux Device Drivers. This recipe assumes that the driver has already been written and shows how to compile and install it. After you’ve followed the steps for this simple module, you will be able to apply them to any other module.

For our example module, add the code in Simple Kernel Module (hello.c) to a file called hello.c.

Listing 55 Simple Kernel Module (hello.c)

#include <linux/module.h>       /* Needed by all modules */
#include <linux/kernel.h>       /* Needed for KERN_INFO */
#include <linux/init.h>         /* Needed for the macros */

static int __init hello_start(void)
{
    printk(KERN_INFO "Loading hello module...\n");
    printk(KERN_INFO "Hello, World!\n");
    return 0;
}

static void __exit hello_end(void)
{
    printk(KERN_INFO "Goodbye Boris\n");
}

module_init(hello_start);
module_exit(hello_end);

MODULE_AUTHOR("Boris Houndleroy");
MODULE_DESCRIPTION("Hello World Example");
MODULE_LICENSE("GPL");

hello.c

When compiling on the Bone, all you need to do is load the Kernel Headers for the version of the kernel you’re running:

bone$ sudo apt install linux-headers-`uname -r`

Note

The quotes around uname -r are backtick characters. On a United States keyboard, the backtick key is to the left of the 1 key.

This took a little more than three minutes on my Bone. The uname -r part of the command looks up what version of the kernel you are running and loads the headers for it.

Next, add the code in Simple Kernel Module (Makefile) to a file called Makefile.

Listing 56 Simple Kernel Module (Makefile)

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

all:
<TAB>make -C $(KDIR) M=$$PWD
	
clean:
<TAB>rm hello.mod.c hello.o modules.order hello.mod.o Module.symvers

Makefile.display

Note

Replace the two instances of <TAB> with a tab character (the key left of the Q key on a United States keyboard). The tab characters are very important to makefiles and must appear as shown.

Now, compile the kernel module by using the make command:

bone$ make
make -C /lib/modules/5.10.168-ti-r62/build M=$PWD
make[1]: Entering directory '/usr/src/linux-headers-5.10.168-ti-r62'
CC [M]  /home/debian/docs.beagleboard.io/books/beaglebone-cookbook/code/07kernel/hello.o
MODPOST /home/debian/docs.beagleboard.io/books/beaglebone-cookbook/code/07kernel/Module.symvers
CC [M]  /home/debian/docs.beagleboard.io/books/beaglebone-cookbook/code/07kernel/hello.mod.o
LD [M]  /home/debian/host/BeagleBoard/docs.beagleboard.io/books/beaglebone-cookbook/code/07kernel/hello.ko
make[1]: Leaving directory '/usr/src/linux-headers-5.10.168-ti-r62'

bone$ ls
Makefile        hello.c   hello.mod.c  hello.o
Module.symvers  hello.ko  hello.mod.o  modules.order

Notice that several files have been created. hello.ko is the one you want. Try a couple of commands with it:

bone$ modinfo hello.ko
filename:       /home/debian/host/BeagleBoard/docs.beagleboard.io/books/beaglebone-cookbook/code/07kernel/hello.ko
license:        GPL
description:    Hello World Example
author:         Boris Houndleroy
depends:
name:           hello
vermagic:       5.10.168-ti-r62 SMP preempt mod_unload modversions ARMv7 p2v8

bone$ sudo insmod hello.ko
bone$ dmesg | tail -4
[  377.944777] lm75 1-004a: hwmon1: sensor 'tmp101'
[  377.944976] i2c i2c-1: new_device: Instantiated device tmp101 at 0x4a
[85819.772666] Loading hello module...
[85819.772687] Hello, World!

The first command displays information about the module. The insmod command inserts the module into the running kernel. If all goes well, nothing is displayed, but the module does print something in the kernel log. The dmesg command displays the messages in the log, and the tail -4 command shows the last four messages. The last two messages are from the module. It worked!

Controlling LEDs by Using SYSFS Entries

Problem

You want to control the onboard LEDs from the command line.

Solution

On Linux, everything is a file that is, you can access all the inputs and outputs, the LEDs, and so on by opening the right file and reading or writing to it. For example, try the following:

bone$ cd /sys/class/leds/
bone$ ls
beaglebone:green:usr0  beaglebone:green:usr2
beaglebone:green:usr1  beaglebone:green:usr3

What you are seeing are four directories, one for each onboard LED. Now try this:

bone$ cd beaglebone\:green\:usr0
bone$ ls
brightness  device  max_brightness  power  subsystem  trigger  uevent
bone$ cat trigger
none nand-disk mmc0 mmc1 timer oneshot [heartbeat]
    backlight gpio cpu0 default-on transient

The first command changes into the directory for LED usr0, which is the LED closest to the edge of the board. The [heartbeat] indicates that the default trigger (behavior) for the LED is to blink in the heartbeat pattern. Look at your LED. Is it blinking in a heartbeat pattern?

Then try the following:

bone$ echo none > trigger
bone$ cat trigger
[none] nand-disk mmc0 mmc1 timer oneshot heartbeat
    backlight gpio cpu0 default-on transient

This instructs the LED to use none for a trigger. Look again. It should be no longer blinking.

Now, try turning it on and off:

bone$ echo 1 > brightness
bone$ echo 0 > brightness

The LED should be turning on and off with the commands.

Controlling GPIOs by Using SYSFS Entries

Problem

You want to control a GPIO pin from the command line.

Solution

Controlling LEDs by Using SYSFS Entries introduces the sysfs. This recipe shows how to read and write a GPIO pin.

Reading a GPIO Pin via sysfs

Suppose that you want to read the state of the P9_42 GPIO pin. (Reading the Status of a Pushbutton or Magnetic Switch (Passive On/Off Sensor) shows how to wire a switch to P9_42.) First, you need to map the P9 header location to GPIO number using Mapping P9_42 header position to GPIO 7, which shows that P9_42 maps to GPIO 7.

Fig. 304 Mapping P9_42 header position to GPIO 7

Next, change to the GPIO sysfs directory:

bone$ cd /sys/class/gpio/
bone$ ls
export  gpiochip0  gpiochip32  gpiochip64  gpiochip96  unexport

The ls command shows all the GPIO pins that have be exported. In this case, none have, so you see only the four GPIO controllers. Export using the export command:

bone$ echo 7 > export
bone$ ls
export  gpio7  gpiochip0  gpiochip32  gpiochip64  gpiochip96  unexport

Now you can see the gpio7 directory. Change into the gpio7 directory and look around:

bone$ cd gpio7
bone$ ls
active_low  direction  edge  power  subsystem  uevent  value
bone$ cat direction
in
bone$ cat value
0

Notice that the pin is already configured to be an input pin. (If it wasn’t already configured that way, use echo in > direction to configure it.) You can also see that its current value is 0—that is, it isn’t pressed. Try pressing and holding it and running again:

bone$ cat value
1

The 1 informs you that the switch is pressed. When you are done with GPIO 7, you can always unexport it:

bone$ cd ..
bone$ echo 7 > unexport
bone$ ls
export  gpiochip0  gpiochip32  gpiochip64  gpiochip96  unexport

Writing a GPIO Pin via sysfs

Now, suppose that you want to control an external LED. Toggling an External LED shows how to wire an LED to P9_14. Mapping P9_42 header position to GPIO 7 shows P9_14 is GPIO 50. Following the approach in Controlling GPIOs by Using SYSFS Entries, enable GPIO 50 and make it an output:

bone$ cd /sys/class/gpio/
bone$ echo 50 > export
bone$ ls
gpio50  gpiochip0  gpiochip32  gpiochip64  gpiochip96
bone$ cd gpio50
bone$ ls
active_low  direction  edge  power  subsystem  uevent  value
bone$ cat direction
in

By default, P9_14 is set as an input. Switch it to an output and turn it on:

bone$ echo out > direction
bone$ echo 1 > value
bone$ echo 0 > value

The LED turns on when a 1 is written to value and turns off when a 0 is written.

Compiling the Kernel

Problem

You need to download, patch, and compile the kernel from its source code.

Solution

This is easier than it sounds, thanks to some very powerful scripts.

Warning

Be sure to run this recipe on your host computer. The Bone has enough computational power to compile a module or two, but compiling the entire kernel takes lots of time and resources.

Downloading and Compiling the Kernel

To download and compile the kernel, follow these steps:

host$ git clone https://git.beagleboard.org/RobertCNelson/ti-linux-kernel-dev # ①
host$ cd ti-linux-kernel-dev
host$ git checkout ti-linux-5.10.y # ②
host$ ./build_deb.sh # ③

Note

If you are using a 64 bit Bone, git checkout ti-linux-arm64-5.10.y

1. The first command clones a repository with the tools to build the kernel for the Bone.

2. When you know which kernel to try, use git checkout to check it out. This command checks out branch ti-linux-5.10.y.

3. build_deb.sh is the master builder. If needed, it will download the cross compilers needed to compile the kernel (gcc is the current cross compiler). If there is a kernel at ~/linux-dev, it will use it; otherwise, it will download a copy to ti-linux-kernel-dev/ignore/linux-src. It will then patch the kernel so that it will run on the Bone.

Note

build_deb.sh may ask you to install additional files. Just run sudo apt install *files* to install them.

After the kernel is patched, you’ll see a screen similar to Kernel configuration menu, on which you can configure the kernel.

Fig. 305 Kernel configuration menu

You can use the arrow keys to navigate. No changes need to be made, so you can just press the right arrow and Enter to start the kernel compiling. The entire process took about 25 minutes on my 8-core host.

The ti-linux-kernel-dev/KERNEL directory contains the source code for the kernel. The ti-linux-kernel-dev/deploy directory contains the compiled kernel and the files needed to run it.

Installing the Kernel on the Bone

The ./build_deb.sh script creates a single .deb file that contains all the files needed for the new kernel. You find it here:

host$ cd ti-linux-kernel-dev/deploy
host$ ls -sh
total 40M
7.7M linux-headers-5.10.168-ti-r62_1xross_armhf.deb  8.0K linux-upstream_1xross_armhf.buildinfo
 33M linux-image-5.10.168-ti-r62_1xross_armhf.deb    4.0K linux-upstream_1xross_armhf.changes
1.1M linux-libc-dev_1xross_armhf.deb

The linux-image- file is the one we want. It contains over 3000 files.

host$ dpkg -c linux-image-5.10.168-ti-r62_1xross_armhf.deb | wc
   3251   19506  379250

The dpkg command lists all the files in the .deb file and the wc counts all the lines in the output. You can see those files with:

host$ dpkg -c linux-image-5.10.168-ti-r62_1xross_armhf.deb | less
drwxr-xr-x root/root         0 2023-06-12 12:57 ./
drwxr-xr-x root/root         0 2023-06-12 12:57 ./boot/
-rw-r--r-- root/root   4763113 2023-06-12 12:57 ./boot/System.map-5.10.168-ti-r62
-rw-r--r-- root/root    191331 2023-06-12 12:57 ./boot/config-5.10.168-ti-r62
drwxr-xr-x root/root         0 2023-06-12 12:57 ./boot/dtbs/
drwxr-xr-x root/root         0 2023-06-12 12:57 ./boot/dtbs/5.10.168-ti-r62/
-rwxr-xr-x root/root     90644 2023-06-12 12:57 ./boot/dtbs/5.10.168-ti-r62/am335x-baltos-ir2110.dtb
-rwxr-xr-x root/root     91362 2023-06-12 12:57 ./boot/dtbs/5.10.168-ti-r62/am335x-baltos-ir3220.dtb
-rwxr-xr-x root/root     91633 2023-06-12 12:57 ./boot/dtbs/5.10.168-ti-r62/am335x-baltos-ir5221.dtb
-rwxr-xr-x root/root     88684 2023-06-12 12:57 ./boot/dtbs/5.10.168-ti-r62/am335x-base0033.dtb

You can see it’s putting things in the /boot directory.

Note: You can also look into the other two .deb files and see what they install.

Move the linux-image- file to your Bone.

host$ scp linux-image-5.10.168-ti-r62_1xross_armhf.deb bone:.

You might have to use debian@192.168.7.2 for bone if you haven’t set everything up.

Now ssh to the bone.

host$ ssh bone
bone$ ls -sh
bin  exercises linux-image-5.10.168-ti-r62_1xross_armhf.deb

Now install it.

bone$ sudo dpkg --install linux-image-5.10.168-ti-r62_1xross_armhf.deb

Wait a while. (Mine took almore 2 minutes.) Once done check /boot.

bone$ ls -sh /boot
total 40M
160K config-4.19.94-ti-r50        4.0K SOC.sh                     4.0K uEnv.txt.orig
180K config-5.10.168-ti-r62       3.5M System.map-4.19.94-ti-r50  9.7M vmlinuz-4.19.94-ti-r50
4.0K dtbs                         4.1M System.map-5.10.168-ti-r62 8.6M vmlinuz-5.10.168-ti-r62
6.4M initrd.img-4.19.94-ti-r50    4.0K uboot
6.8M initrd.img-5.10.168-ti-r62   4.0K uEnv.txt

You see the new kernel files along with the old files. Check uEnv.txt.

bone$ head /boot/uEnv.txt
#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0
# uname_r=4.19.94-ti-r50
uname_r=5.10.168-ti-r62

I added the commented out uname_r line to make it easy to switch between versions of the kernel.

Reboot and test out the new kernel.

bone$ sudo reboot

Using the Installed Cross Compiler

Problem

You have followed the instructions in Compiling the Kernel and want to use the cross compiler it has downloaded.

Tip

You can cross-compile without installing the entire kernel source by running the following:

host$ sudo apt install gcc-arm-linux-gnueabihf

Then skip down to Setting Up Variables.

Solution

Compiling the Kernel installs a cross compiler, but you need to set up a couple of things so that it can be found. Compiling the Kernel installed the kernel and other tools in a directory called ti-linux-kernel-dev. Run the following commands to find the path to the cross compiler:

host$ cd ti-linux-kernel-dev/dl
host$ ls
gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux
gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux.tar.xz

Here, the path to the cross compiler contains the version number of the compiler. Yours might be different from mine. cd into it:

host$ cd gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux
host$ ls
20130415-gcc-linaro-arm-linux-gnueabihf  bin  libexec
arm-linux-gnueabihf                      lib  share

At this point, we are interested in what’s in bin:

host$ cd bin
host$ ls
arm-linux-gnueabihf-addr2line     arm-linux-gnueabihf-gfortran
arm-linux-gnueabihf-ar            arm-linux-gnueabihf-gprof
arm-linux-gnueabihf-as            arm-linux-gnueabihf-ld
arm-linux-gnueabihf-c+*           arm-linux-gnueabihf-ld.bfd
arm-linux-gnueabihf-c++filt       arm-linux-gnueabihf-ldd
arm-linux-gnueabihf-cpp           arm-linux-gnueabihf-ld.gold
arm-linux-gnueabihf-ct-ng.config  arm-linux-gnueabihf-nm
arm-linux-gnueabihf-elfedit       arm-linux-gnueabihf-objcopy
arm-linux-gnueabihf-g+*           arm-linux-gnueabihf-objdump
arm-linux-gnueabihf-gcc           arm-linux-gnueabihf-pkg-config
arm-linux-gnueabihf-gcc-4.7.3     arm-linux-gnueabihf-pkg-config-real
arm-linux-gnueabihf-gcc-ar        arm-linux-gnueabihf-ranlib
arm-linux-gnueabihf-gcc-nm        arm-linux-gnueabihf-readelf
arm-linux-gnueabihf-gcc-ranlib    arm-linux-gnueabihf-size
arm-linux-gnueabihf-gcov          arm-linux-gnueabihf-strings
arm-linux-gnueabihf-gdb           arm-linux-gnueabihf-strip

What you see are all the cross-development tools. You need to add this directory to the $PATH the shell uses to find the commands it runs:

host$ pwd
/home/yoder/BeagleBoard/ti-linux-kernel-dev/dl/\
    gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux/bin

host$ echo $PATH
    /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:\
    /usr/games:/usr/local/games

The first command displays the path to the directory where the cross-development tools are located. The second shows which directories are searched to find commands to be run. Currently, the cross-development tools are not in the $PATH. Let’s add it:

host$ export PATH=`pwd`:$PATH
host$ echo $PATH
/home/yoder/BeagleBoard/ti-linux-kernel-dev/dl/\
    gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415_linux/bin:\
    /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:\
    /usr/games:/usr/local/games

Note

Those are backtick characters (left of the “1” key on your keyboard) around pwd.

The second line shows the $PATH now contains the directory with the cross-development tools.

Setting Up Variables

Now, set up a couple of variables to know which compiler you are using:

host$ export ARCH=arm
host$ export CROSS_COMPILE=arm-linux-gnueabihf-

These lines set up the standard environmental variables so that you can determine which cross-development tools to use. Test the cross compiler by adding Simple helloWorld.c to test cross compiling (helloWorld.c) to a file named _helloWorld.c_.

Listing 57 Simple helloWorld.c to test cross compiling (helloWorld.c)

#include <stdio.h>

int main(int argc, char **argv) {
  printf("Hello, World! \n");
}

helloWorld.c

You can then cross-compile by using the following commands:

host$ ${CROSS_COMPILE}gcc helloWorld.c
host$ file a.out
a.out: ELF 32-bit LSB executable, ARM, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.6.31,
BuildID[sha1]=0x10182364352b9f3cb15d1aa61395aeede11a52ad, not stripped

The file command shows that a.out was compiled for an ARM processor.

Applying Patches

Problem

You have a patch file that you need to apply to the kernel.

Solution

Simple kernel patch file (hello.patch) shows a patch file that you can use on the kernel.

Listing 58 Simple kernel patch file (hello.patch)

From eaf4f7ea7d540bc8bb57283a8f68321ddb4401f4 Mon Sep 17 00:00:00 2001
From: Jason Kridner <jdk@ti.com>
Date: Tue, 12 Feb 2013 02:18:03 +0000
Subject: [PATCH] hello: example kernel modules

---
 hello/Makefile   |    7 +++++++
 hello/hello.c    |   18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 0 deletions(-)
 create mode 100644 hello/Makefile
 create mode 100644 hello/hello.c

diff --git a/hello/Makefile b/hello/Makefile
new file mode 100644
index 0000000..4b23da7
--- /dev/null
+++ b/hello/Makefile
@@ -0,0 +1,7 @@
+obj-m := hello.o
+
+PWD   := $(shell pwd)
+KDIR  := ${PWD}/..
+
+default:
+	make -C $(KDIR) SUBDIRS=$(PWD) modules
diff --git a/hello/hello.c b/hello/hello.c
new file mode 100644
index 0000000..157d490
--- /dev/null
+++ b/hello/hello.c
@@ -0,0 +1,22 @@
+#include <linux/module.h>       /* Needed by all modules */
+#include <linux/kernel.h>       /* Needed for KERN_INFO */
+#include <linux/init.h>         /* Needed for the macros */
+
+static int __init hello_start(void)
+{
+    printk(KERN_INFO "Loading hello module...\n");
+    printk(KERN_INFO "Hello, World!\n");
+    return 0;
+}
+
+static void __exit hello_end(void)
+{
+    printk(KERN_INFO "Goodbye Boris\n");
+}
+
+module_init(hello_start);
+module_exit(hello_end);
+
+MODULE_AUTHOR("Boris Houndleroy");
+MODULE_DESCRIPTION("Hello World Example");
+MODULE_LICENSE("GPL");

hello.patch

Here’s how to use it:

• Install the kernel sources (Compiling the Kernel).

• Change to the kernel directory (+cd ti-linux-kernel-dev/KERNEL+).

• Add Simple kernel patch file (hello.patch) to a file named hello.patch in the ti-linux-kernel-dev/KERNEL directory.

• Run the following commands:

host$ cd ti-linux-kernel-dev/KERNEL
host$ patch -p1 < hello.patch
patching file hello/Makefile
patching file hello/hello.c

The output of the patch command apprises you of what it’s doing. Look in the hello directory to see what was created:

host$ cd hello
host$ ls
hello.c  Makefile

Building and Installing Kernel Modules shows how to build and install a module, and Creating Your Own Patch File shows how to create your own patch file.

Creating Your Own Patch File

Problem

You made a few changes to the kernel, and you want to share them with your friends.

Solution

Create a patch file that contains just the changes you have made. Before making your changes, check out a new branch:

host$ cd ti-linux-kernel-dev/KERNEL
host$ git status
# On branch master
nothing to commit (working directory clean)

Good, so far no changes have been made. Now, create a new branch:

host$ git checkout -b hello1
host$ git status
# On branch hello1
nothing to commit (working directory clean)

You’ve created a new branch called hello1 and checked it out. Now, make whatever changes to the kernel you want. I did some work with a simple character driver that we can use as an example:

host$ cd ti-linux-kernel-dev/KERNEL/drivers/char/
host$ git status
# On branch hello1
# Changes not staged for commit:
#   (use "git add file..." to update what will be committed)
#   (use "git checkout -- file..." to discard changes in working directory)
#
#   modified:   Kconfig
#   modified:   Makefile
#
# Untracked files:
#   (use "git add file..." to include in what will be committed)
#
#   examples/
no changes added to commit (use "git add" and/or "git commit -a")

Add the files that were created and commit them:

host$ git add Kconfig Makefile examples
host$ git status
# On branch hello1
# Changes to be committed:
#   (use "git reset HEAD file..." to unstage)
#
#   modified:   Kconfig
#   modified:   Makefile
#   new file:   examples/Makefile
#   new file:   examples/hello1.c
#
host$ git commit -m "Files for hello1 kernel module"
[hello1 99346d5] Files for hello1 kernel module
4 files changed, 33 insertions(+)
create mode 100644 drivers/char/examples/Makefile
create mode 100644 drivers/char/examples/hello1.c

Finally, create the patch file:

host$ git format-patch master --stdout > hello1.patch