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CHAPTER 4. LIVERAM DISKS 4.5. KEXECBOOTS

The

kexecboot

kernel’s command line arguments are set in the default recipe ﬁle, i.e.

recipes/kexecboot/linux-kexecboot.inc

. The

CMDLINE

variable is set conditionally, depending

on the platform (

any

poodle

akita

collie

spitz

and

hx4700

). The default kernel conﬁguration

is read from ﬁle

defconfig

and in the

do_configure_append()

section, some edits are made to

remove various conﬁgure options, and add others.

CONFIG_BLK_DEV_INITRD

and

CONFIG_KEXEC

are

enabled, and the initramfs source ﬁle is set to

initramfs.cpio.gz

. Kernel modules are disabled

and the kernel is built with the conﬁguration in ﬁle .config.

The

require

line in

linux-kexecboot.inc

includes

../linux/linux.inc

, which builds the

kexecboot kernel. Conditional tests decide whether

OABI

EABI

support should be included, set

the Linux logo type, Thumb instruction set support, endianness and other options.

The kernel name is set with the following lines:

KERNEL_IMAGE_BASE_NAME = "${KERNEL_IMAGETYPE}-kexecboot-${PV}-${PR}-${MACHINE}"

KERNEL_IMAGE_SYMLINK_NAME = "${KERNEL_IMAGETYPE}-kexecboot-${MACHINE}"

Where is KERNEL IMAGETYPE

set?

The

do_stage()

and

do_install()

steps are set to empty functions, meaning that they will

have no effect: the kernel and initramfs are built only, and no other actions occur. The generated

images will be written in various locations Which locations?

For example, build/tmp/deploy/glibc/images/c7x0/ dir contains:

Angstrom-initramfs-kexecboot-image-glibc-ipk-2009.X-test-20100106-c7x0.rootfs.cpio.gz

Angstrom-initramfs-kexecboot-image-glibc-ipk-2009.X-test-20100106-c7x0.rootfs.cpio.lzma

initramfs-kexecboot-image-c7x0.cpio.gz -> Angstrom-initramfs-kexecboot-image-glibc-ipk-2009.X-test-20100106-c7x0.rootfs.cpio.gz

initramfs-kexecboot-image-c7x0.cpio.lzma -> Angstrom-initramfs-kexecboot-image-glibc-ipk-2009.X-test-20100106-c7x0.rootfs.cpio.lzma

modules-2.6.26-r12-c7x0.tgz

zImage-2.6.26-r12-c7x0.bin

zImage-c7x0.bin -> zImage-2.6.26-r12-c7x0.bin

zImage-kexecboot-2.6.26-r15-c7x0.bin

zImage-kexecboot-2.6.32-r15-c7x0.bin

zImage-kexecboot-c7x0.bin -> zImage-kexecboot-2.6.32-r15-c7x0.bin

USE_MACHINE_KERNEL

is deﬁned when building kexecboot,

/proc/cpuinfo

is scanned for a

Hardware:

line and if present, the

Hardware

result is converted to lower case, spaces are replaced

with underscores and

/mnt/boot/zImage-

is prepended to it. For example, in the case of the Sharp

SL-5500 (’Collie’), /proc/cpuinfo has the line

Hardware : Sharp-Collie

The line is checked for a colon and if found,

Sharp-Collie

would be appended to the

zImage-

string,

so /mnt/boot/zImage-Sharp-Collie is looked for.

4.5.2.2 Remarks

4.5.3 Role

A kexecboot kernel is, in a more precise way, a kernel that has the kexec feature called; this feature can

load other, normal kernels in and boot into them. This allows the main kernel used in

Angstr

om to

be upgraded without ﬂashing the device whole. The kexecboot kernel needs to be small and slim

enough that it can ﬁt into the NAND, yet be able to handle the managing RAM initdisk used to

ﬁnd and select the new kernel to boot off of. It should also (in minimal variant) have support all

’bootable’ storages (NAND, CF, SD/MMC, etc).

Similar projects include “Two Kernel Monte” and CoreBoot.

Kexecboot development was started to solve following problems:

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