[PATCH v8 0/5] Add support for containerized root filesystems

[Silvano Cirujano Cuesta <silvano.cirujano-cuesta@siemens.com>]

v8: cosmetic changes in docs and small fix in CI script

v7: issues in sample configurations and CI script fixed and tested on
two different CI environments.

This patch series provides support for containerized root filesystems,
for both target images and SDKs.

For containerized target images the new image type `container-img` has
been added.

For containerized SDKs the task `populate_sdk` has been extended.

Containerized root filesystems are easy to distribute and run, enabling
this way following scenarios:
 - Use ISAR to build container images meant to be run only in containers.
 - Use the same ISAR configuration to build images for containers, VMs
   and bare-metal.
 - Easy SDK distribution and "installation".
 - Quickly testing certain applications in the workstation using the
   target root filesystem.

In order to build containerized target root filesystems `IMAGE_TYPE` has
to be `container-img`, additionally the container image format can be
selected with the variable `CONTAINER_FORMATS`. The default format is
`docker-archive`.

In order to build containerized SDKs the variable `SDK_FORMAT` has to
provide any of the supported container formats (e.g. `docker-archive`).
The default format is the legacy non-containerized: `tar_xz`.

It also provides a sample machine, multiconfigs and ci-testing.

More information about its usage is documented in the file
docs/user_manual.md.

A PoC/demo of this functionality (only the SDK part) has been created
based on the project https://github.com/siemens/meta-iot2050.
Jan Kiszka already tested and liked it! =>
https://github.com/siemens/meta-iot2050/issues/86#issuecomment-768907845

Successful builds of both containerized target and SDK are available on
the same PoC project:
 - https://github.com/Silvanoc/meta-iot2050/actions/runs/558311580
 - https://github.com/Silvanoc/meta-iot2050/actions/runs/558311581
and also the resulting images:
 - https://github.com/users/Silvanoc/packages/container/package/meta-iot2050%2Fiot2050-debian-arm64
 - https://github.com/users/Silvanoc/packages/container/package/meta-iot2050%2Fiot2050-debian-sdk-arm64

In order to get a feeling about its usage (you need Docker or Podman),
follow these simple copy&paste instructions:
https://github.com/Silvanoc/meta-iot2050/blob/master/kas/BUILDING-SDK-CONTAINER.md#running-the-sdk
Build instructions are available in the upper part of that document.

Two new dependencies (umoci and skopeo -backporting from bullseye to
buster works easily) are required to create containerized root
filesystems (as specified in the documentation).

Typical container image management actions (e.g. push an image to a
container image regitry) are out of scope. Available tools (Docker,
Skopeo, Buildah, Podman,...) should be used for these actions.

A patch will follow this one to get the dependencies into the container
images being provided by the project
https://github.com/siemens/kas (for `kas-container`, for example).

Silvano Cirujano Cuesta (5):
  classes: add root filesystem containerizing class
  classes: add new image type 'container-img'
  sdk: add support for containerized sdk
  docs: document creation of container images
  ci: add container image sample configurations

 doc/user_manual.md                            | 179 ++++++++++++++++++
 meta-isar/conf/local.conf.sample              |   3 +
 meta-isar/conf/machine/container.conf         |   5 +
 .../conf/multiconfig/container-bullseye.conf  |   4 +
 .../conf/multiconfig/container-buster.conf    |   4 +
 .../conf/multiconfig/container-stretch.conf   |   4 +
 meta/classes/container-img.bbclass            |  18 ++
 .../classes/image-container-extension.bbclass |  82 ++++++++
 meta/classes/image-sdk-extension.bbclass      |  42 +++-
 meta/classes/image.bbclass                    |   1 +
 scripts/ci_build.sh                           |  29 ++-
 11 files changed, 363 insertions(+), 8 deletions(-)
 create mode 100644 meta-isar/conf/machine/container.conf
 create mode 100644 meta-isar/conf/multiconfig/container-bullseye.conf
 create mode 100644 meta-isar/conf/multiconfig/container-buster.conf
 create mode 100644 meta-isar/conf/multiconfig/container-stretch.conf
 create mode 100644 meta/classes/container-img.bbclass
 create mode 100644 meta/classes/image-container-extension.bbclass

-- 
2.30.2