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Build Your Custom OpenWrt Image

2021/05/10 | 访问量： 次 OpenWrt

This guides to build your OpenWrt Image integrated with custom application step by step.

Setup OpenWrt

Pre-requisites

Debian / Ubuntu

sudo apt update
sudo apt install build-essential ccache ecj fastjar file g++ gawk \
gettext git java-propose-classpath libelf-dev libncurses5-dev \
libncursesw5-dev libssl-dev python python2.7-dev python3 unzip wget \
python3-distutils python3-setuptools rsync subversion swig time \
xsltproc zlib1g-dev

CentOS / Fedora

sudo dnf --skip-broken install bash-completion bzip2 gcc gcc-c++ git \
make ncurses-devel patch perl-Data-Dumper perl-Thread-Queue python2 \
python3 rsync tar unzip wget perl-base perl-File-Compare \
perl-File-Copy perl-FindBin diffutils which

For other Linux distributions, you can take this for reference.

Build OpenWrt form source code

You need leave the sudo privileged mode to get better cross-compile by ctrl + d or exit.

  1. Get the OpenWrt source code

    git clone https://git.openwrt.org/openwrt/openwrt.git
cd openwrt

  2. Build from main branch or stable release branch

    # To build from a specific version
git branch
git checkout <branch name>
# Or just skip to 3 to build from main branch

  3. Update and install feeds

    ./scripts/feeds update -a
./scripts/feeds install -a

  4. Configure

    make menuconfig

    E.g. for target “TL-WR841N v11” Wi-Fi router do following:

    • “Target System” ⇒ “Select” ⇒ “Atheros AR7xxx/AR9xxx” ⇒ “Select”
    • “Subtarget” ⇒ “Select” ⇒ “Devices with small flash” ⇒ “Select”
    • “Target Profile” ⇒ “Select” ⇒ “TP-LINK TL-WR841N/ND v11” ⇒ “Select”

    To exit OpenWrt configuration and save target with options settings do following:

    • “Exit” ⇒ “Yes”

  5. Tool Chain

    make toolchain/install

    The target-independent tools and the toolchain are deployed to the staging_dir/host/ and staging_dir/toolchain/ directories. This applies to the executables built in the above section as well the pre-built executables available in the SDK. We can adjust the PATH variable:

    export PATH=/home/icn/openwrt/staging_dir/host/bin:$PATH

  6. Build image

    make
# For faster compiling, use `make -j N`, where N is the number of CPU cores + 1.

    And the target image will be generated into ./bin/target/...

Create your own application

Locate your application

Suppose we create a project named hellosdewan.

mkdir hellosdewan
cd hellosdewan
pwd
# /home/icn/hellosdewan

We create the sole source code file named hellosdewan.c.

touch hellosdewan.c

And input the following content:

#include <stdio.h>
 
int main(void)
{
    printf("\nHello, sdewan!\n\n");
    return 0;
}

Compile and test

Our example application is a c application.

gcc -c -o hellosdewan.o hellosdewan.c -Wall
gcc -o hellosdewan hellosdewan.o

And then, run the hellosdewan binary

./hellosdewan
# Hello, sdewan!

Generate the application package

Create package and configure it

Firstly create a directory to store your own application, like the openwrt,

mkdir -p myapps/test/hellosdewan
cd myapps/test/hellosdewan
pwd
# /home/icn/myapps/test/hellosdewan

Then we need deliver a package manifest file for hellosdwan application, which is responsible for describing the package, what it does and provide instructions on where to obtain the source code, how to build it and which should be contained in the final installable package.

In current directory, create a Makefile:

include $(TOPDIR)/rules.mk

# Name, version and release number
# The name and version of your package are used to define the variable to point to the build directory of your package: $(PKG_BUILD_DIR)
PKG_NAME:=hellosdewan
PKG_VERSION:=1.0
PKG_RELEASE:=1

# Source settings (i.e. where to find the source codes)
# This is a custom variable, used below
SOURCE_DIR:=/home/icn/myapps/test/hellosdewan

include $(INCLUDE_DIR)/package.mk

# Package definition; instructs on how and where our package will appear in the overall configuration menu ('make menuconfig')
define Package/hellosdewan
        SECTION:=test
        CATEGORY:=MyApps
        TITLE:=Hello, sdewan!
endef

# Package description; a more verbose description on what our package does
define Package/hellosdewan/description
        A simple "Hello, sdewan!" -application.
endef

# Package preparation instructions; create the build directory and copy the source code.
# The last command is necessary to ensure our preparation instructions remain compatible with the patching system.
define Build/Prepare
        mkdir -p $(PKG_BUILD_DIR)
        cp $(SOURCE_DIR)/* $(PKG_BUILD_DIR)
        $(Build/Patch)
endef

# Package build instructions; invoke the target-specific compiler to first compile the source file, and then to link the file into the final executable
define Build/Compile
        $(TARGET_CC) $(TARGET_CFLAGS) -o $(PKG_BUILD_DIR)/hellosdewan.o -c $(PKG_BUILD_DIR)/hellosdewan.c
        $(TARGET_CC) $(TARGET_LDFLAGS) -o $(PKG_BUILD_DIR)/$1 $(PKG_BUILD_DIR)/hellosdewan.o
endef

# Package install instructions; create a directory inside the package to hold our executable, and then copy the executable we built previously into the folder
define Package/hellosdewan/install
        $(INSTALL_DIR) $(1)/usr/bin
        $(INSTALL_BIN) $(PKG_BUILD_DIR)/hellosdewan $(1)/usr/bin
endef

# This command is always the last, it uses the definitions and variables we give above in order to get the job done
$(eval $(call BuildPackage,hellosdewan))

Integrate the package to build system

OpenWrt build system uses a file named feeds.conf.default which indicates the package feeds that will be made available during the firmware configuration stage.

pwd
# /home/icn/openwrt
cat feed.conf.default
`
src-git packages https://git.openwrt.org/feed/packages.git
src-git luci https://git.openwrt.org/project/luci.git
src-git routing https://git.openwrt.org/feed/routing.git
src-git telephony https://git.openwrt.org/feed/telephony.git
#src-git video https://github.com/openwrt/video.git
#src-git targets https://github.com/openwrt/targets.git
#src-git management https://github.com/openwrt-management/packages.git
#src-git oldpackages http://git.openwrt.org/packages.git
#src-link custom /usr/src/openwrt/custom-feed
`

Modify the file to link to myapps package feed with vim or other editor in feeds.conf.default:

src-link myapps /home/icn/myapps

Updating and installing feeds

The new feed is defined, so update the build system

pwd
# /home/icn/openwrt
./scripts/feeds update myapps
./scripts/feeds install -a -p myapps

Build image and test

Build image with custom application

Re-configure your openwrt build system

pwd
# /home/icn/openwrt
make menuconfig

In the menu list, we could find the category named MyApps and enter into this category and choose the application we deployed named hellosdewan here. Save the configuration and exit.

The changes will be stored to .config, then start to build the image

make -j 70
# To locate the error, you can run `make -j1 V=sc`

Import image and test

After finishing the image build, we can find the rootfs of the image in the ./bin directory

pwd
# /home/icn/openwrt
# Dive into the target to find the `rootfs` image
cd ./bin/targets/x86/64
ls openwrt-x86-64-generic-rootfs.tar.gz

Import the image to docker as a docker container

sudo docker import openwrt-x86-64-generic-rootfs.tar.gz myapps:hellosdewan

Then the image is imported into docker as myapps and tag is hellosdewan. We can run the docker image and test the application hellosdewan

sudo docker run -ti myapps:hellosdewan hellosdewan
# Hello, sdewan!

Note you can build the opkg package solely

pwd
# /home/icn/openwrt
make package/hellosdewan/compile
# The `hellosdewan_1.0-1_x86_64.ipk` will be on `./bin/packages/x86_64/myapps`
# And you can use `opkg` to directly install it
opkg install <path-to-package>/hellosdewan_1.0-1_x86_64.ipk
# Or you can remove the installation
opkg remove hellosdewan

Patch your application

Prepare

Check the tool for patch is ready

pwd
# /home/icn/openwrt
quilt --version
# the path of tools like quilt in under `./staging_dir/host/bin/`

Prepare the source code and navigate into the build directory.

make package/hellosdewan/{clean,prepare} QUILT=1
cd build_dir/target-x86_64_musl/hellosdewan-1.0
quilt push -a

Create a simple patch

quilt new 000-add.patch
# If editing existing files
quilt edit hellosdewan.c
# If adding new fiels
quilt add function.c
quilt add function.h
touch function.c
touch function.h
quilt edit function.c
quilt edit function.h

function.c

int add(int a, int b)
{
    return a + b;
}

function.h

int add(int, int);

And we can review the change and accept changes as content of patch

quilt diff
quilt refresh

Include the patch

Migrate the patch data into package

pwd
# /home/icn/openwrt
make package/hellosdewan/update

We now can review the package feed folder and see the changes

ls -la /home/icn/myapps/test/hellosdewan
ls -la /home/icn/hellosdewan

OpenWrt build system have migrated the patch to the package manifest folder.

Then build and check the new files and changes are present in the build directory

pwd
# /home/icn/openwrt
make package/hellosdewan/{clean,prepare}
ls -la build_dir/target-x86_64_musl/hellosdewan-1.0

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