[[PageOutline]]

= Buildroot
A Linux kernel without a root filesystem (aka rootfs) is useless. There are many sources for root filesystems including complete Linux distributions like Ubuntu (often too big, or limited in arch availability), pre-built root filesystems from vendors (often too limited), root filesystems built manually with Busybox (still often too limited) and more. There are Embedded Linux build systems which try to be more flexible like !OpenEmbedded, Yocto, and OpenWrt but these tend to be not easy to understand or quick to setup. Buildroot tends to be a much more simplistic approach using standard makefiles, can produce a root filesystem in minutes, and has 1000+ userspace libs/apps available.

Using a buildroot rootfs is extremely useful for:
 * Small fast booting self-contained systems (the default busybox rootfs is typically ~1.5MB)
 * Kernel development (using [#initrd initrd] or [#initramfs initramfs] options)
 * Using its toolchain externally

''' !*!*!*!* WARNING !*!*!*!* '''

Buildroot is a powerful and low footprint rootfs. However, it is for advanced developers due to the fact there is a lot of manual configuration. Gateworks recommends developing with a more friendly ready to go rootfs, such as Ubuntu where package management is provided by default. Development time will be shortened greatly with Ubuntu. Once operating properly on Ubuntu, one can move over to buildroot to optimize. 

'''Note''' that Buildroot requires all packages to be installed at the time of building. There is not a package manager like many other distributions have (like [wiki:ubuntu Ubuntu], such as apt-get to quickly install pre-compiled package binaries.



== Suggested Tools
Suggested tools to include for kernel development:
 * dropbear for SSH
 * benchmarksiozone, bonnie++, LTP, netperf, ramspeed, stress, lmbench, iostat, memtester, etc
 * debug tools; evtest, i2c-tools, devmem2, pciutils, usbutils, libv4l, alsa-utils, linux-firmware, mii-diag, iperf, iw
 * filesystem tools: resize2fs (BR2_PACKAGE_E2FSPROGS_RESIZE2FS) adds 1.2MB for 2.4MB cpio

== Building
{{{#!bash
git clone https://github.com/buildroot/buildroot.git
cd buildroot
make menuconfig # configure
make -j8
ls output/images
}}}
 * Note that like many build systems sources will be downloaded from the network during the build process
 * The .config file contains all the configuration options from the {{{make menuconfig}}}
 * see sections below on configuration tips for various platforms

For platform specific notes see below:
 * [#venice Gateworks Venice (imx8mm)]
 * [#newport Gateworks Newport (cn80xx)]
 * [#ventana Gateworks Ventana (imx6)]

References:
 * https://buildroot.org
 * https://buildroot.org/downloads/manual/manual.html
 * http://free-electrons.com/pub/conferences/2013/kernel-recipes/rootfs-kernel-developer/rootfs-kernel-developer.pdf


[=#initrd]
== initrd (initial ramdisk)
The initial RAM disk (initrd) is an initial root file system that is mounted prior to when the real root file system is available. The initrd is bound to the kernel and loaded as part of the kernel boot procedure.

An {{{initrd}}} is a 'cpio' image (an archive created with the Unix {{{cpio}}} tool) thus you need to have 
BR2_TARGET_ROOTFS_CPIO enabled and optionally one of the compression formats supported by your kernel).

If using U-Boot 'bootm' be sure to enable BR2_TARGET_ROOTFS_CPIO_UIMAGE which runs 'mkimage' on output/images/rootfs.cpio to create a 'uramdisk'.

Example booting Linux kernel with device-tree and initrd using U-Boot 'bootm':
 * Bootloader:
{{{#!bash
setexpr fdt_addr $loadaddr
setexpr linux_addr $fdt_addr + 0x20000 # allow 128KB for FDT
setexpr rd_addr $linux_addr + 0x4000000 # allow 64MB for kernel
setenv bootargs "console=${console},${baudrate}"
setenv fsload tftpboot # for network load
$fsload $fdt_addr $fdt_file2 && $fsload $linux_addr uImage && $fsload $rd_addr uramdisk && bootm $linux_addr $rd_addr $fdt_addr
}}}
  - In the above example you can modify fsload to load for your storage interface, device, and filesystem (ie "setenv fsload 'fatload mmc 0:1'" for loading from fist mmc controller first partition fatfs filesystem)


[=#initramfs]
== initramfs
The buildroot root filesystem can also be built statically into a kernel eliminating the need to have a separate kernel and ramdisk as in the [#initrd initrd] option above.

To build a rootfs suitable for use as an initramfs:
 - Select target arch
 - Configure toolchain or point to external toolchain
 - System configuration - select devtmpfs /dev management method and ensure serial port for the getty is correct
 - Filesystem images - select cpio format
 - use {{{make}}} to build - your rootfs will be in output/images/rootfs.cpio and will build within minutes
 - a default config using busybox will be about 1.5MiB

Make sure your kernel has the following:
 - CONFIG_DEVTMPFS=y - to get devtmpfs support, to provide a dynamic /dev
 - CONFIG_INITRAMFS_SOURCE="/path/to/buildroot/output/images/rootfs.cpio" - path to your cpio
 - CONFIG_INITRAMFS_COMPRESSION_GZIP=y - compression algorithm
 - CONFIG_INITRAMFS_ROOT_UID=0 - root user id
 - CONFIG_INITRAMFS_ROOT_GID=0 - root group id


If using buildbot to build kernel add the following to automatically build a kernel using to buildroot rootfs as an initramfs:
 * BR2_TARGET_ROOTFS_INITRAMFS=y

See also:
 * [wiki:linux/initramfs linux/initramfs]


[=#toolchain]
== Using Buildroot toolchain externally
Buildroot builds its own GCC toolchain and using this externally can be useful. The toolchain generated by Buildroot is located by default in {{{output/host/}}} and the simplest way to use it to to add {{{output/host/bin/}}} to your PATH then and use the version of gcc tools there.

For example:
{{{#!bash
export PATH=$PWD/output/host/bin:$PATH
export CROSS_COMPILE=arm-linux-
export ARCH=arm
}}}

It is possible to relocate this toolchain making it easy for distribution using {{{make sdk}}} which prepares the toolchain to be relocatable and creates a tarball in the {{{output/host/}}} directory. The {{{relocate-sdk.sh}}} script in the tarball can be used to update paths.

See the full documentation in docs/manual/using-buildroot-toolchain.txt

[=#busybox]
== Busybox config
Busybox is used by default for all of the tools in the rootfs built by buildroot. If you want to alter the default configuration of busybox itself you can access it via {{{make menuconfig}}}:
 * Target packages -> !BusyBox -> !BusyBox configuration file to use
 * defaults to package/busybox/busybox.config


[=#overlay]
== Adding or modifying files in the rootfs
A common need is to add or modify existing files in the root filesystem. Buildroot makes this very easy by allowing a set of directories to be specified that it will overlay on the target root filesytem.

Examples
 * Add firmware for the Sterling LWB wireless module (obtained from https://www.lairdconnect.com/wireless-modules/wi-fi-bt-modules/sterling-lwb)
  1. make menuconfig and set BR2_ROOTFS_OVERLAY=files
  2. create an overlay directory. For example, add firmware for the LAIRD sterling-lwb wifi module:
{{{#!bash
mkdir -p files
tar xvf firmware-7.0.0.326.tar.bz2 -C files
}}}
  3. build with 'make'
  4. notice your files are now in output/target/lib/firmware/brcm

If you wish to modify a file simply provide your version of it in your overlay and it will be copied over the original. If you wish to remove a file you can provide a 0-byte version of the file which may meet your needs.

Additionally you can use {{{BR2_ROOTFS_POST_BUILD_SCRIPT}}} to make any changes after buildroot builds but before the rootfs images are assembled.


[=#init]
== Create a custom init script
The {{{init}}} program is the first userspace program started by the kernel (with PID 1) and is responsible for starting the userspace services. There are three different types of init provided by buildroot which can be chosen under 'System cnfiguration, Init system' but the default solution provided by busybox is usually just fine for embedded systems.

The busybox init system is configured via an {{{/etc/inittab{{{ which has a fairly simple syntax (see [https://git.busybox.net/busybox/tree/examples/inittab here]). The important items in this file do the following:
 * mount various psuedo-filesystems such as proc
 * execute /etc/init.d/rcS on startup
 * execute /etc/init.d/rcK on shutdown
 * kick off a getty process on the console tty allowing login

The /etc/init.d/rcS script executes the scripts in /etc/init.d which match the 'S??*' pattern. If you want a custom init script you can add one here. A good example to start with is the /etc/init.d/S40network example.

For more information see the Buildroot user manual 'init system' section.



[=#modules]
== Loading kernel modules
Typical Linux systems have a hotplug manager such as {{{udev}}} running in the background that loads modules for detected devices. Without such as system you must do this manually. Once easy solution is to do this at boot time via an init script.

Examples:
 * Auto load modules for devices detected at boot as well as a non-device specific module such as 'batman-adv':
  1. make menuconfig and set BR2_ROOTFS_OVERLAY=files
  2. create an init script that loads modules for detected devices and modules listed in {{{/etc/modules}}}:
{{{#!bash
mkdir -p files/etc/init.d
cat << \EOF > files/etc/init.d/S30modules
#!/bin/sh

case "$1" in
  start)
    printf "Loading modules:"
    # load modules for detected devices
    find /sys/ -name modalias -print0 | xargs -0 sort -u -z | xargs -0 modprobe -abq

    # load modules from /etc/modules
    [ -r /etc/modules ] || exit 0
    while read module args; do
        case "$module" in
                ""|"#"*) continue ;;
        esac

        # attempt to load modules
        modprobe ${module} ${args} >/dev/null
    done < /etc/modules
    ;;
esac
EOF
chmod +x files/etc/init.d/S30modules
}}}
  3. create an {{{/etc/modules}}} file with extra modules and arguments you wish to load:
{{{#!bash
cat << \EOF > files/etc/modules
batman-adv
EOF
}}}
  3. build with 'make'



[=#kernel]
== Kernel Configuration
If you are using buildroot to build a kernel {{{BR2_KERNEL}}}, you can choose where to get the kernel config (the in-kernel arch default, another in-kernel defconfig, or a custom kernel defconfig). Regardless of your initial kernel config choice you can later modify the kernel configuration via {{{make linux-menuconfig}}}. Following that you can use {{{make linux-savedefconfig}}} to create a defconfig file in the Linux build directory and {{{make linux-update-defconfig}}} to save the Linux defconfig to the path specified by {{{BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE}}}.


[=#venice]
== Venice (IMX8MM)
The following details pertain to buildroot 2020.08 although newer versions will likely be similar if not the same.

The Venice product family is based on the i.MX8MM SoC which has 4x Cortex-A53 CPU cores. Therefore the 'BR2_aarch64' is really the only important configuration which produces binaries executable on arm64 CPU's.

To build a root filesystem only:
{{{#!bash
cat << EOF > configs/venice_minimal_defconfig
# arm64 arch
BR2_aarch64=y
# filesystem options
BR2_TARGET_ROOTFS_TAR_XZ=y
EOF
make venice_minimal_defconfig
make -j8
}}}

This builds output/images/root.tar.xz consisting of a ~1.7MiB root filesystem (when uncompressed) in 5 to 10 minutes of building on a typical Linux desktop.

If you also want buildroot to build a Gateworks v5.4.45 kernel with a minimal kernel config and a self-contained minimal root filesystem you would use the following:
{{{#!bash
cat << EOF > configs/venice_kernel_defconfig
# arm64 arch
BR2_aarch64=y
# toolchain
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
# kernel
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-venice.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v5.4.45-venice"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="venice_minimal_kernel_defconfig"
# filesystem options
BR2_TARGET_ROOTFS_INITRAMFS=y
BR2_TARGET_ROOTFS_TAR_XZ=y
EOF
# fetch minimal kernel config for venice
wget http://dev.gateworks.com/buildroot/venice/minimal/venice_minimal_kernel_defconfig
make venice_kernel_defconfig
make -j8
}}}

This produces a ~10MB output/images/Image in 10 to 15 minutes of building on a typical Linux desktop. This is a kernel Image containing the root filesystem in a ramdisk. This is a really easy way to get a read-only minimal Linux image that boots fast and does not access flash storage.

Perhaps an even more useful image would contain tools for provisioning a FLASH emmc device:
{{{#!bash
cat << EOF > configs/venice_example_defconfig
# arm64 arch
BR2_aarch64=y
# toolchain
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_TOOLCHAIN_BUILDROOT_LOCALE=y
BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
# kernel
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-venice.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v5.4.45-venice"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="venice_minimal_kernel_defconfig"
# filesystem options
BR2_TARGET_ROOTFS_CPIO_XZ=y
BR2_TARGET_ROOTFS_INITRAMFS=y
BR2_TARGET_ROOTFS_TAR_XZ=y
# extra utils needed for basic testing and provisioning emmc
BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
BR2_PACKAGE_COREUTILS=y
BR2_PACKAGE_PV=y
BR2_PACKAGE_STRESS=y
BR2_PACKAGE_E2FSPROGS=y
BR2_PACKAGE_E2FSPROGS_RESIZE2FS=y
BR2_PACKAGE_PARTED=y
BR2_PACKAGE_EVTEST=y
BR2_PACKAGE_GPTFDISK=y
BR2_PACKAGE_GPTFDISK_SGDISK=y
BR2_PACKAGE_I2C_TOOLS=y
BR2_PACKAGE_MEMTESTER=y
BR2_PACKAGE_PCIUTILS=y
BR2_PACKAGE_PICOCOM=y
BR2_PACKAGE_LIBUSB=y
BR2_PACKAGE_TCPDUMP=y
BR2_PACKAGE_SCREEN=y
BR2_PACKAGE_UTIL_LINUX=y
BR2_PACKAGE_UTIL_LINUX_BINARIES=y
BR2_PACKAGE_TAR=y
# extra utils needed for uboot images and env
BR2_PACKAGE_UBOOT_TOOLS=y
BR2_PACKAGE_UBOOT_TOOLS_MKIMAGE=y
# fetch minimal kernel config
wget http://dev.gateworks.com/buildroot/newport/minimal/venice_minimal_kernel_defconfig
make venice_example_defconfig
make -j8
}}}
 * Note you can easily add your own files and scripts to this image by setting BR2_ROOTFS_OVERLAY to a directory or directories where your files are

This produces a ~15MiB output/images/Image in 10 to 15 minutes of building on a typical Linux desktop. This is a kernel Image containing the root filesystem in a ramdisk. This is a really easy way to get a read-only minimal Linux image that boots fast and has the tools necessary to create a partition table and filesystems

If you need to add back or modify kernel features you can do so with:
{{{#!bash
make linux-menuconfig # make your changes
make -j8
# save and update the defconfig once you are happy with it
make linux-savedefconfig linux-update-defconfig
}}}

You can boot a Kernel+ramdisk via U-Boot like this:
 * load from network tftpserver
{{{#!bash
tftpboot $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}
 * load from microSD with ext/fat filesystem
{{{#!bash
load mmc 1:1 $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}
 * load from USB with ext/fat filesystem
{{{#!bash
usb start; load usb 0:1 $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}

A prebuilt image can be found [http://dev.gateworks.com/buildroot/venice/minimal here] which contains an image built from the above venice_example_defconfig 
 - Gateworks Venice Linux 5.4.45 kernel
 - glibc with wide-char, locale, and g++ support
 - screen (BR2_PACKAGE_SCREEN)
 - pciutils (BR2_PACKAGE_PCIUTILS)
 - libusb (BR2_PACKAGE_LIBUSB)
 - eudev (BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV) (required for usbutils)
 - usbutils (BR2_PACKAGE_USBUTILS)
 - stress (BR2_PACKAGE_STRESS)
 - evtest (BR2_PACKAGE_EVTEST)
 - parted/gdisk/sgdisk disk partitioning tools
 - ext filesystem support mkfs/resize2fs (BR2_PACKAGE_E2FSPROGS_RESIZE2FS)
 - u-boot image creation tools (mkimage/fw_setenv/fw_printenv)


[=#newport]
== Newport (CN80XX)
The following details pertain to buildroot 2020.08 although newer versions will likely be similar if not the same.

The Newport product family is based on the CN80xx SoC which has 4x Cortex-A53 like compatible CPU cores. Therefore the 'BR2_aarch64' is really the only important configuration which produces binaries executable on arm64 CPU's.

To build a root filesystem only:
{{{#!bash
cat << EOF > configs/arm64_minimal_defconfig
# arm64 arch
BR2_aarch64=y
# filesystem options
BR2_TARGET_ROOTFS_TAR_XZ=y
EOF
make arm64_minimal_defconfig
make -j8
}}}

This builds output/images/root.tar.xz consisting of a ~1.7MiB root filesystem (when uncompressed) in 5 to 10 minutes of building on a typical Linux desktop.

If you also want buildroot to build a Gateworks v5.4.45 kernel with a minimal kernel config attached as an initrd you can use this:
{{{#!bash
cat << EOF > configs/newport_kernel_defconfig
# arm64 arch
BR2_aarch64=y
# toolchain
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
# kernel
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-newport.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v5.4.45-newport"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="newport_minimal_kernel_defconfig"
# filesystem options
BR2_TARGET_ROOTFS_TAR_XZ=y
BR2_TARGET_ROOTFS_INITRAMFS=y
EOF
# fetch minimal kernel config
wget http://dev.gateworks.com/buildroot/newport/minimal/newport_minimal_kernel_defconfig
make newport_kernel_defconfig
make -j8
}}}

This produces a ~9MiB output/images/Image in 10 to 15 minutes of building on a typical Linux desktop. This is a kernel Image containing the root filesystem in a ramdisk. This is a really easy way to get a read-only minimal Linux image that boots fast and does not access flash storage.

Perhaps an even more useful image would contain tools for provisioning a FLASH emmc device:
{{{#!bash
cat << EOF > configs/newport_provision_defconfig
# arm64 arch
BR2_aarch64=y
# toolchain
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_TOOLCHAIN_BUILDROOT_LOCALE=y
BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
# kernel
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-newport.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v5.4.45-newport"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="newport_minimal_kernel_defconfig"
# filesystem options
BR2_TARGET_ROOTFS_CPIO_XZ=y
BR2_TARGET_ROOTFS_INITRAMFS=y
BR2_TARGET_ROOTFS_TAR_XZ=y
# extra utils needed for basic testing and provisioning emmc
BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
BR2_PACKAGE_COREUTILS=y
BR2_PACKAGE_PV=y
BR2_PACKAGE_STRESS=y
BR2_PACKAGE_E2FSPROGS=y
BR2_PACKAGE_E2FSPROGS_RESIZE2FS=y
BR2_PACKAGE_PARTED=y
BR2_PACKAGE_EVTEST=y
BR2_PACKAGE_GPTFDISK=y
BR2_PACKAGE_GPTFDISK_SGDISK=y
BR2_PACKAGE_I2C_TOOLS=y
BR2_PACKAGE_MEMTESTER=y
BR2_PACKAGE_PCIUTILS=y
BR2_PACKAGE_PICOCOM=y
BR2_PACKAGE_LIBUSB=y
BR2_PACKAGE_TCPDUMP=y
BR2_PACKAGE_SCREEN=y
BR2_PACKAGE_UTIL_LINUX=y
BR2_PACKAGE_UTIL_LINUX_BINARIES=y
BR2_PACKAGE_TAR=y
# extra utils needed for uboot images and env
BR2_PACKAGE_UBOOT_TOOLS=y
BR2_PACKAGE_UBOOT_TOOLS_MKIMAGE=y
EOF
# fetch minimal kernel config
wget http://dev.gateworks.com/buildroot/newport/minimal/newport_minimal_kernel_defconfig
make newport_kernel_defconfig
make -j8
}}}
 * Note you can easily add your own files and scripts to this image by setting BR2_ROOTFS_OVERLAY to a directory or directories where your files are

This produces a ~15MiB output/images/Image in 10 to 15 minutes of building on a typical Linux desktop. This is a kernel Image containing the root filesystem in a ramdisk. This is a really easy way to get a read-only minimal Linux image that boots fast and has the tools necessary to create a partition table and filesystems

You can boot a Kernel+ramdisk via U-Boot like this:
 * load from network tftpserver
{{{#!bash
tftpboot $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}
 * load from microSD with ext/fat filesystem
{{{#!bash
load mmc 1:1 $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}
 * load from USB with ext/fat filesystem
{{{#!bash
usb start; load usb 0:1 $kernel_addr_r Image && booti $kernel_addr_r - $fdtcontroladdr
}}}

A prebuilt image can be found [http://dev.gateworks.com/buildroot/newport/minimal here] which contains an image built from the above newport_example_defconfig 
 - Gateworks Newport Linux 5.4.45 kernel
 - glibc with wide-char, locale, and g++ support
 - screen (BR2_PACKAGE_SCREEN)
 - pciutils (BR2_PACKAGE_PCIUTILS)
 - libusb (BR2_PACKAGE_LIBUSB)
 - eudev (BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV) (required for usbutils)
 - usbutils (BR2_PACKAGE_USBUTILS)
 - stress (BR2_PACKAGE_STRESS)
 - evtest (BR2_PACKAGE_EVTEST)
 - parted/gdisk/sgdisk disk partitioning tools
 - ext filesystem support mkfs/resize2fs (BR2_PACKAGE_E2FSPROGS_RESIZE2FS)
 - u-boot image creation tools (mkimage/fw_setenv/fw_printenv)


=== Building .ext4 filesystem and compressed disk image

In the event you choose to use Buildroot but wish to avoid the drawbacks of a ramdisk you can install it to a block storage device. For this you will need to create a .ext4 filesystem image.  This example will utilize the Linux-Newport branch of the mainline 4.14.4 kernel. 

Prerequisite for this procedure you will need to have:

* Downloaded and configured the [wiki:/newport/bsp Newport BSP], many of the tools used will be provided by it.
* The [http://dev.gateworks.com/newport/kernel/linux-newport.tar.xz linux-newport.tar.xz] kernel tarball.  
* The latest [http://dev.gateworks.com/newport/boot_firmware/firmware-newport.img firmware-newport.img] boot firmware if you would like to create a compressed disk image.

With the Newport BSP installed and Buildroot cloned set target architecture to AArch64:
{{{#!bash
cd buildroot
cat << EOF > configs/my_defconfig
BR2_aarch64=y
EOF
}}}

Now:
{{{#!bash
make my_defconfig
make -j8
}}}

After the build completes:
* Export the location of the rootfs.tar located in your buildroot/output/images folder.
{{{#!bash
ROOTFS=${PWD}/output/images/rootfs.tar
}}}
* Create a tmp_mnt directory at a location of your discression, this is your temporary mounting point for compiling the filesystem.
{{{#!bash
mkdir tmp_mnt
TMP_MNT=${PWD}/tmp_mnt  
}}}
* Create a filesystem of a specific size. It will be expandable later using resize2fs, make it large enough to fit what you have in your current build.   
{{{#!bash
OUT=buildroot-newport.ext4
SIZEMB=1536 # 1.5GB
truncate -s ${SIZEMB}M ${OUT}
mkfs.ext4 -q -F -L rootfs ${OUT}
}}}
* Mount this file to your 'tmp_mnt' directory
{{{#!bash
sudo mount ${OUT} ${TMP_MNT}
}}}
* Extract the Buildroot rootfs.tar and linux-newport.tar.xz which was downloaded to this mount point.
{{{#!bash
sudo tar -C ${TMP_MNT} -xf ${ROOTFS}
sudo tar -C ${TMP_MNT} -xf linux-newport.tar.xz
}}}
* Convert the kernel 'Image' (uncompressed Kernel) to a fit image.  For this you will need a tool from your Newport BSP directory, in this example the path to the BSP directory is named ${NEWPORT_BSP}.
{{{#!bash
mv ${TMP_MNT}/boot/Image vmlinux
gzip -f vmlinux
mkimage -f auto -A arm64 -O linux -T kernel -C gzip -n "buildroot-newport" \                            
   -a 20080000 -e 20080000 -d vmlinux.gz tmp_mnt/boot/kernel.itb
}}}
* Create U-Boot bootscript using the existing Ubuntu one from the Newport BSP, use mkimage to add the u-boot header.
{{{#!bash
mkimage -A arm64 -T script -C none -d ${NEWPORT_BSP}/newport/ubuntu.scr ${TMP_MNT}/boot/newport.scr
}}}
* Unmount temporary mount point, and compress the .ext4 file to be used with the u-boot command 'gzwrite'.
{{{#!bash
umount ${TMP_MNT}
rm -rf ${TMP_MNT}
gzip -k -f ${OUT}
}}}

To load this root file system without disturbing the existing boot firmware tftpboot can be used:

* Boot your Newport SBC, at the prompt "Hit any key to stop autoboot" press a key. 
* Execute the following commands.
{{{#!bash
setenv ipaddr <your boards IP>
setenv serverip <your TFTP server IP>
setenv dev 0
setenv image buildroot-newport.ext4.gz
run update_rootfs
}}}

To create a disk image from the .ext4 file:

* Creating a disk image is useful if you would like to overwrite the existing boot firmware when the image is flashed.  
{{{#!bash
# http://dev.gateworks.com/newport/boot_firmware/firmware-newport.img
cp firmware-newport.img buildroot-newport.img
# copy buildroot rootfs .ext4 filesystem to image with an offset 
dd if=buildroot-newport.ext4 of=buildroot-newport.img bs=16M seek=1
# compress it
gzip -k -f buildroot-newport.img
}}}


[=#ventana]
== Ventana (IMX6)
The following details pertain to buildroot 2020.08 although newer versions will likely be similar if not the same.

The Ventana product family is based on the i.MX6 SoC which has ARM Cortex-A9 CPU cores. Therefore we will tune the compiler to build arm32 code with support for ARM NEON and VFP.

To build a root filesystem only:
{{{#!bash
cat << EOF > configs/imx6_minimal_defconfig
# arm cortex-a9 cpu
BR2_arm=y
BR2_cortex_a9=y
BR2_ARM_ENABLE_NEON=y
BR2_ARM_ENABLE_VFP=y
BR2_ARM_FPU_VFPV3=y
# filesystem options
BR2_TARGET_ROOTFS_CPIO_XZ=y
EOF
make imx6_minimal_defconfig
make -j8
}}}

This builds output/images/root.tar.xz consisting of a ~1.7MiB root filesystem (when uncompressed) in 5 to 10 minutes of building on a typical Linux desktop.

If you also want buildroot to build a Gateworks v5.4.45 kernel with a minimal kernel config and a self-contained minimal root filesystem you would add the following the your defconfig:
{{{#!bash
cat << EOF > configs/ventana_kernel_defconfig
# arm cortex-a9 cpu
BR2_arm=y
BR2_cortex_a9=y
BR2_ARM_ENABLE_NEON=y
BR2_ARM_ENABLE_VFP=y
BR2_ARM_FPU_VFPV3=y
# toolchain
BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
# kernel
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-imx6.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="gateworks_5.4.45"
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="gwventana_minimal_kernel_defconfig"
# filesystem options
BR2_TARGET_ROOTFS_TAR_XZ=y
BR2_TARGET_ROOTFS_INITRAMFS=y
EOF
# fetch minimal kernel config for ventana
wget http://dev.gateworks.com/buildroot/ventana/minimal/gwventana_minimal_kernel_defconfig
make ventana_kernel_defconfig
make -j8
}}}

This produces a ~7MiB compressed kernel image in output/images/uImage containing the ~1.7MiB root filesystem in 15 to 20 minutes of building on a typical Linux desktop.

If you need add back or modify kernel features you can do so with:
{{{#!bash
make linux-menuconfig # make your changes
make -j8
# save and update the defconfig once you are happy with it
make linux-savedefconfig linux-update-defconfig
}}}

To boot a kernel+ramdisk on Ventana via the bootloader with a tftpserver copy output/images/uImage and output/images/*.dtb to your tftpserver and use:
 * load from network tftpserver
{{{#!bash
setenv bootargs console=ttymxc1,115200
setenv fsload tftpboot
setenv bootdir . # set this to the prefix of your tftp dir
run loadfdt && $fsload $loadaddr $bootdir/uImage && bootm $loadaddr - $fdt_addr
}}}
 * load from microSD with ext/fat filesystem
{{{#!bash
setenv bootargs console=ttymxc1,115200
setenv fsload load mmc 0:1
setenv bootdir . # set this to the prefix of your tftp dir
run loadfdt && $fsload $loadaddr $bootdir/uImage && bootm $loadaddr - $fdt_addr
}}}
 * load from USB with ext/fat filesystem
{{{#!bash
setenv bootargs console=ttymxc1,115200
setenv fsload load usb 0:1
usb start
setenv bootdir . # set this to the prefix of your tftp dir
run loadfdt && $fsload $loadaddr $bootdir/uImage && bootm $loadaddr - $fdt_addr
}}}

A prebuilt image can be found [http://dev.gateworks.com/buildroot/ventana/minimal here] which contains:
 * Gateworks Linux 5.4.45 kernel (minimal kernel features)
 * resize2fs (BR2_PACKAGE_E2FSPROGS_RESIZE2FS)
 * uclibc
 * screen (BR2_PACKAGE_SCREEN)
 * pciutils (BR2_PACKAGE_PCIUTILS)
 * libusb (BR2_PACKAGE_LIBUSB)
 * eudev (BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV) (required for usbutils)
 * usbutils (BR2_PACKAGE_USBUTILS) 
 * gdisk/sgdisk disk partitioning tools:
  - gdisk/sgdisk (BR2_PACKAGE_GPTFDISK/BR2_PACKAGE_GPTFDISK_SGDISK)
 * stress (BR2_PACKAGE_STRESS)
 * evtest (BR2_PACKAGE_EVTEST)
 * ubi/ubifs tools



[=#swupdate]
== SWUpdate
SWUpdate is a framework for providing firmware udpates. It is extremely flexible and provides support for many different scenarios. Because it exists as a package for buildroot it is a great choice for providing firmware updates when using a buildroot solution.

Here we will provide an example of building an SWUpdate Over-The-Air (OTA) update for buildroot with the following considerations:
 - Newport
 - Symmetric Image Update (Two copies of rootfs which works well when your filesystem is relatively small compared to memory/flash space)
 - We will not bother updating boot firmware (can be added later)
 - We will not bother updating GSC firmware (can be added later)
 - We will build the Gateworks 5.45 kernel for newport with a minimal kernel config
 - We will use an uncompressed kernel image (just avoids needing to kernel a kernel.itb)
 - We will use a modified uboot environment to handle our root partition  toggling

Here are the relevant files to add to your buildroot directory:
 * '''configs/newport_swupdate_defconfig''': Buildroot defconfig (represents the minimal 'changes' made to buildroot default config):
{{{#!bash
BR2_aarch64=y
BR2_KERNEL_HEADERS_5_4=y

# we will add some files to the rootfs from the 'overlay' subdir
BR2_ROOTFS_OVERLAY="overlay"

#
# Kernel:
#  we will build the gateworks linux kernel using arm64 defconfig 
#  plus some additional configs via newport_kernel_defconfig
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_GIT=y
BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/Gateworks/linux-newport.git"
BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v5.4.45-newport"
BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="newport_kernel_defconfig"
BR2_LINUX_KERNEL_INSTALL_TARGET=y

#
# Packages:
#  we need u-boot env tools for fw_setenv support in our scripts
#  we need zlib/openssl/libconfig/json for various features in SWUpdate we enable
#  we will use swupdate.config to configure SWUpdate
BR2_PACKAGE_UBOOT_TOOLS=y
BR2_PACKAGE_ZLIB=y
BR2_PACKAGE_OPENSSL=y
BR2_PACKAGE_LIBCONFIG=y
BR2_PACKAGE_JSON_C=y
BR2_PACKAGE_LIBCURL=y
BR2_PACKAGE_SWUPDATE=y
BR2_PACKAGE_SWUPDATE_CONFIG="swupdate.config"

#
# Filesystem
#
BR2_TARGET_ROOTFS_EXT2=y
BR2_TARGET_ROOTFS_EXT2_4=y
BR2_TARGET_ROOTFS_EXT2_GZIP=y
}}}
  - Note that SWUpdate reuqires ZLIB if we are going to use gzip compression
 * '''newport_kernel_defconfig''': Kernel config fragment that adds OcteonTX and newport drivers to arm64 kernel defconfig
{{{#!bash
# Additionally OcteonTX peripheral drivers
CONFIG_PCI_HOST_THUNDER_PEM=y
CONFIG_PCI_HOST_THUNDER_ECAM=y
CONFIG_CAN=y
CONFIG_CAN_MCP251X=y
CONFIG_THUNDER_NIC_PF=y
CONFIG_THUNDER_NIC_VF=y
CONFIG_MDIO_BITBANG=y
CONFIG_I2C=y
CONFIG_I2C_THUNDERX=y
CONFIG_SPI_THUNDERX=y
CONFIG_GPIO_THUNDERX=y
CONFIG_MMC_CAVIUM_THUNDERX=y
CONFIG_EDAC_THUNDERX=y
CONFIG_EXT4_FS=y
# Gateworks Newport GSC drivers
CONFIG_MFD_GATEWORKS_GSC=y
CONFIG_SENSORS_GSC=y
}}}
 * '''overlay/etc/fw_env.config''': config file for u-boot env tools fw_setenv
{{{#!bash
# Device offset size
/dev/mmcblk0 0xff0000 0x8000
/dev/mmcblk0 0xff8000 0x8000
}}}
  - Note that this file is whitespace sensitive
 * '''swupdate.config''': config file to build swupdate executable which resides on your firmware and drives the update process
{{{#!bash
# We do not need MTD or LUA support
# CONFIG_MTD is not set
# CONFIG_LUA is not set
CONFIG_SIGNED_IMAGES=y
CONFIG_ENCRYPTED_IMAGES=y
# Suricatta provides support for fetching updates via a Hawkbit server if desired
CONFIG_SURICATTA=y
CONFIG_SURICATTA_SSL=y
CONFIG_SURICATTA_STATE_CHOICE_BOOTLOADER=y
# We need the raw handler to image to an MMC partition 
CONFIG_RAW=y
# We need the shellscript handler for our update.sh shellscript
CONFIG_SHELLSCRIPTHANDLER=y
# We need the bootloader handler to alter the u-boot environment
CONFIG_BOOTLOADERHANDLER=y
}}}
 * '''sw-description''': part of the actual firmware OTA which describes the process and file manifest of the update image. See [https://sbabic.github.io/swupdate/sw-description.html# here] for syntax
{{{#!bash
software =
{
        version = "0.1.0";
        description = "Firmware update for XXXXX Project";

        /* images installed to the system */
        images: (
                {
                        filename = "rootfs.ext4.gz";
                        device = "/dev/update";
                        type = "raw";
                        compressed = true;
                }
        );

        scripts: (
                {
                        filename = "update.sh";
                        type = "shellscript";
                }
        );
}
}}}
 - '''update.sh''': This is the script that SWUpdate runs which we use as both a preinst and psotinst script (via cmdline). We determine the current root device and, flip it, and symlink /dev/update to the device to update to. We don't have to do the image install as we've configured SWUpdate to do that for us in sw-descrption images.
{{{#!bash
#!/bin/sh

if [ $# -lt 1 ]; then
        exit 0;
fi

function get_current_root_device
{
        for i in `cat /proc/cmdline`; do
                if [ ${i:0:5} = "root=" ]; then
                        CURRENT_ROOT="${i:5}"
                fi
        done
}

# ping-pong between /dev/mmcblk0p2 and /dev/mmcblk0p3
# (adapt for your partitioning scheme and/or root device type)
function get_update_part
{
        CURRENT_PART="${CURRENT_ROOT:-/dev/mmcblk0p2}"
        if [ $CURRENT_PART = "/dev/mmcblk0p2" ]; then
                UPDATE_PART="3";
        else
                UPDATE_PART="2";
        fi
}

function get_update_device
{
        UPDATE_ROOT=${CURRENT_ROOT%?}${UPDATE_PART}
}


if [ $1 == "preinst" ]; then
        # get the current root device
        get_current_root_device

        # get the device to be updated
        get_update_part
        get_update_device

        # create a symlink for the update process
        ln -sf $UPDATE_ROOT /dev/update
fi

if [ $1 == "postinst" ]; then
        # get the current root device
        get_current_root_device

        # get the device to be updated
        get_update_part
        get_update_device

        # toggle rootpart between 2 and 3
        # we do it twice to write to both primary/secondary env
        fw_setenv mmcbootpart $UPDATE_PART
        fw_setenv mmcbootpart $UPDATE_PART
fi
}}}

Once this is in place you can use the following to build:
{{{#!bash
# build buildroot rootfs
make newport_swupdate_defconfig
make
# create a private/public key combo for signature verifcation
openssl genrsa -out swupdate-priv.pem # private
openssl rsa -in swupdate-priv.pem -out swupdate-public.pem -outform PEM -pubout # public
# sign the sw-description
openssl dgst -sha256 -sign swupdate-priv.pem sw-description > sw-description.sig
# build swupdate image
cp output/images/rootfs.ext4.gz .
for i in sw-description sw-description.sig update.sh rootfs.ext4.gz; do
        echo $i; done | cpio -ov -H crc > my-software.swu
}}}
 * Note that you can skip the inclusion of sw-description.sig and the pub/priv key if you don't care about signatures and have not define CONFIG_SIGNED_IMAGES in your swupdate.config

Here are some one-time steps you will need to do to your boot firmware:
 * create an MBR partition table that defines LinuxA and LinuxB partitions we will ping-pong between. Note that the FATFS must not be changed from the original boot firmware generated MBR and that we also create a general userdata partition.
{{{#!bash
# 1: 2048:30720 (15MiB) FAT12 (required by boot firmware)
# 2: 65536:4194304 (2GiB) LinuxA
# 3: 4259840:4194304 (2GiB) LinuxB
# 4: 8454144:4194304 (2GiB) userdata
wget -q https://raw.githubusercontent.com/Gateworks/bsp-newport/sdk-10.1.1.0-newport/ptgen
/bin/bash ptgen \
        -p 0x01:2048:30720 \
        -p 0x83:65536:4194304 \
        -p 0x83:4259840:4194304 \
        -p 0x83:8454144:4194304 \
        > $BUILDROOT/output/images/mbr.bin
}}}
 * In U-Boot we will update the partition table:
{{{#!bash
tftpboot ${loadaddr} mbr.bin && mmc dev 0 && mmc write ${loadaddr} 0 1 # mbr is at 0 and 1 sector long
}}}
  - Note that if you ever update the entire boot firmware it will over-write this partition table so you will want to take care to not overwrite that portion
 * In U-Boot we will install the original rootfs to the first Linux partition offset (LinuxA)
{{{#!bash
tftpboot ${loadaddr} rootfs.ext4.gz && gzwrite mmc 0 ${loadaddr} ${filesize} 0x100000 0x2000000 # rootfsA is at 0x2000000 (64MiB) and we use a 1MiB buffer
}}}
 * In U-Boot we will alter the env to use the '''mmcbootpart''' env variable that our update.sh manipulates after a successful update:
{{{#!bash
setenv mmcbootpart 2
setenv bootcmd "setenv bootargs 'console=${console} root=/dev/mmcblk0p${mmcbootpart} rootwait rw usbcore.autosuspend=-1 kpti=0; load mmc 0:${mmcbootpart} ${kernel_addr_r} boot/Image' && booti ${kernel_addr_r} - ${fdtcontroladdr}"
saveenv
}}} 
  - Note the single quotes around the bootargs value as we do not want U-Boot to expand the args until runtime

After you boot to buildroot you can fetch and install the SWUpdate image with:
{{{#!bash
# bring up networking
udhcpc -i eth0
# fetch image
cd /tmp
wget http://myserver/my-software.swu
wget http://myserver/swupdate-public.pem
swupdate -i mysoftware.swu -k swupdate-public.pem
}}}
 * Note that you can skip the -k param have not enabled signed images via CONFIG_SIGNED_IMAGES in your swupdate.config

Note that if you require support for SWUpdate to complete an install that isn't already there (for example you want to add the capability to update GSC firmware via the gsc_update utility) you will either need to a) add a static linked version of that tool to your image or b) do a 2-stage update where you add the required tools first, then use them in a future update

== Other Buildroot Wiki Pages
See also:
 * [wiki:buildroot/qt Using QT Framework on Buildroot]
 * [wiki:buildroot/gstreamer Using gstreamer on Buildroot]