Upgrade Buildroot to 2019.02 LTS

[afbjorklund]

Currently minikube is running Buildroot 2018.05, featuring Linux 4.16 (downgraded to 4.15)
These are now out of support, since they were short-lived and not supported for the long term.

BUILDROOT_BRANCH ?= 2018.05.3

(the previous long-term versions would have been Buildroot 2018.02 and Linux 4.14)

We should upgrade to Buildroot 2019.02, featuring Linux 4.19 (both of them long term support)
Currently the minor versions of each are 2019.02.6 and 4.19.76, but this might change later.

BUILDROOT_BRANCH ?= 2019.02.6

Doing so, we should look into the VirtualBox guest additions module that caused issues:

#2986

VBOX_GUEST_VERSION = 5.1.38

VirtualBox 5.1.x is no longer supported! https://www.virtualbox.org/wiki/Changelog-5.1

BR2_LINUX_KERNEL_CUSTOM_VERSION=y
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.15"

VirtualBox 5.2.32 (released July 16 2019)

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This also addresses #5007

Might also consider #5105 ?

UPDATED, for new Buildroot release:
2019.02.5, Released September 2nd, 2019
2019.02.6, Released October 4th, 2019

[afbjorklund]

Some facts about the build host: (in the buildroot-image, and also leaks a bit in the build)

• Ubuntu 18.04 LTS ("bionic")
• GCC 7.4.0 (https://packages.ubuntu.com/bionic-updates/gcc)
• VirtualBox 5.2.32 (https://packages.ubuntu.com/bionic-updates/virtualbox)

Other details as per https://minikube.sigs.k8s.io/docs/contributing/iso/ - which needs updating...

Even if we are not considering moving to a Docker build, we should at least make sure it works.
Currently there are some issues when running on a Mac*, and generally it hasn't been tried much.
We should at least update the documentation, so that there is a way to build the Buildroot image.
In somewhat related news we might want to upgrade toolbox, but that would be a separate issue.

• see documentation: use a case-sensitive disk image when building the ISO on mac #3752

[afbjorklund]

Besides virtualbox issues, we also got some systemd issues with the "toolbox" command...

Seems like there now is a requirement on a working system dbus, that is not being fulfilled.
Failed to open system bus: No such file or directory

Most likely the systemd-nspawn commands need some new magic flags, in order to work ?
--register=no --keep-unit

Any way, it (toolbox) used to work fine with systemd-237 but now breaks with systemd-240.

[afbjorklund]

I tried building the ISO in a docker container, and it seemed to work.

The only issue (besides the volume mount), seems to be the cache.
Currently we store it in /tmp/.buildroot-ccache, and throw it away...

We might want to mount ~/.buildroot-ccache from the build host, or so ?

cache directory                     /home/anders/.buildroot-ccache
primary config                      /home/anders/.buildroot-ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
stats zero time                     Sun Oct 13 15:41:54 2019
cache hit (direct)                  2438
cache hit (preprocessed)            1742
cache miss                         33900
cache hit rate                     10.98 %
called for link                     2260
called for preprocessing            1615
multiple source files                  3
compiler produced stdout               3
compile failed                      1814
preprocessor error                   504
can't use precompiled header           1
bad compiler arguments               300
unsupported source language           14
autoconf compile/link               7841
unsupported compiler option          168
unsupported code directive             9
output to stdout                       3
no input file                       2866
cleanups performed                     0
files in cache                     80017
cache size                           1.1 GB
max cache size                       5.0 GB