tools/buildroot: Add support for generating Linux target system images

Integrate buildroot into devlib in order to ease building kernel and
root filesystem images via 'generate-kernel-initrd.sh' helper script.

As its name suggests, the script builds kernel image which also includes
an initial RAM disk per default config files located under
configs/<arch>/.

Provide config files for buildroot and Linux kernel as well as a
post-build.sh script which tweaks (e.g., allowing root login on SSH)
target's root filesystem.

doc/tools.rst talks about details of kernel and rootfs configuration.

Signed-off-by: Metin Kaya <metin.kaya@arm.com>

tools/buildroot/configs/aarch64/arm-power_aarch64_defconfig

@@ -0,0 +1,17 @@
+BR2_aarch64=y
+BR2_cortex_a73_a53=y
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_ROOT_PASSWD="root"
+BR2_SYSTEM_DHCP="eth0"
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/arm-power/post-build.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/arm-power/aarch64/linux.config"
+BR2_LINUX_KERNEL_XZ=y
+BR2_PACKAGE_OPENSSH=y
+# BR2_PACKAGE_OPENSSH_SANDBOX is not set
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_TARGET_ROOTFS_CPIO_XZ=y
+BR2_TARGET_ROOTFS_INITRAMFS=y
+# BR2_TARGET_ROOTFS_TAR is not set

tools/buildroot/configs/aarch64/linux.config

@@ -0,0 +1,36 @@
+CONFIG_SCHED_MC=y
+CONFIG_UCLAMP_TASK=y
+CONFIG_SCHED_SMT=y
+CONFIG_KERNEL_XZ=y
+CONFIG_SYSVIPC=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_CGROUPS=y
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_INITRAMFS_SOURCE="${BR_BINARIES_DIR}/rootfs.cpio"
+# CONFIG_RD_GZIP is not set
+# CONFIG_RD_BZIP2 is not set
+# CONFIG_RD_LZMA is not set
+# CONFIG_RD_LZO is not set
+# CONFIG_RD_LZ4 is not set
+# CONFIG_RD_ZSTD is not set
+CONFIG_SMP=y
+# CONFIG_GCC_PLUGINS is not set
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+CONFIG_PCI=y
+CONFIG_PCI_HOST_GENERIC=y
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_NETDEVICES=y
+CONFIG_VIRTIO_NET=y
+CONFIG_INPUT_EVDEV=y
+CONFIG_SERIAL_AMBA_PL011=y
+CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
+CONFIG_VIRTIO_CONSOLE=y
+CONFIG_VIRTIO_PCI=y
+CONFIG_TMPFS=y

tools/buildroot/configs/post-build.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+set -eux
+
+# Enable root login on SSH
+sed -i 's/#PermitRootLogin.*/PermitRootLogin yes/' "${TARGET_DIR}/etc/ssh/sshd_config"
+
+# Increase the number of available channels so that devlib async code can
+# exploit concurrency better.
+sed -i 's/#MaxSessions.*/MaxSessions 100/' "${TARGET_DIR}/etc/ssh/sshd_config"
+sed -i 's/#MaxStartups.*/MaxStartups 100/' "${TARGET_DIR}/etc/ssh/sshd_config"
+
+# To test Android bindings of ChromeOsTarget
+mkdir -p "${TARGET_DIR}/opt/google/containers/android"
+

tools/buildroot/configs/x86_64/arm-power_x86_64_defconfig

@@ -0,0 +1,16 @@
+BR2_x86_64=y
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_ROOT_PASSWD="root"
+BR2_SYSTEM_DHCP="eth0"
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/arm-power/post-build.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/arm-power/x86_64/linux.config"
+BR2_LINUX_KERNEL_XZ=y
+BR2_PACKAGE_OPENSSH=y
+# BR2_PACKAGE_OPENSSH_SANDBOX is not set
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_TARGET_ROOTFS_CPIO_XZ=y
+BR2_TARGET_ROOTFS_INITRAMFS=y
+# BR2_TARGET_ROOTFS_TAR is not set

tools/buildroot/configs/x86_64/linux.config

@@ -0,0 +1,31 @@
+CONFIG_KERNEL_XZ=y
+CONFIG_SYSVIPC=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_CGROUPS=y
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_INITRAMFS_SOURCE="${BR_BINARIES_DIR}/rootfs.cpio"
+# CONFIG_RD_GZIP is not set
+# CONFIG_RD_BZIP2 is not set
+# CONFIG_RD_LZMA is not set
+# CONFIG_RD_LZO is not set
+# CONFIG_RD_LZ4 is not set
+# CONFIG_RD_ZSTD is not set
+CONFIG_SMP=y
+# CONFIG_GCC_PLUGINS is not set
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+CONFIG_PCI=y
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_NETDEVICES=y
+CONFIG_VIRTIO_NET=y
+CONFIG_INPUT_EVDEV=y
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+CONFIG_VIRTIO_PCI=y
+CONFIG_TMPFS=y