[PATCH v6 0/5] Add support for containerized root filesystems

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

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 testing configurations

 doc/user_manual.md                            | 127 ++++++++++++++++++
 meta-isar/conf/machine/container.conf         |   5 +
 .../conf/multiconfig/container-bullseye.conf  |   4 +
 .../conf/multiconfig/container-buster.conf    |   4 +
 .../conf/multiconfig/container-focal.conf     |   4 +
 .../conf/multiconfig/container-stretch.conf   |   4 +
 meta/classes/container-img.bbclass            |  18 +++
 .../classes/image-container-extension.bbclass |  81 +++++++++++
 meta/classes/image-sdk-extension.bbclass      |  42 +++++-
 meta/classes/image.bbclass                    |   1 +
 scripts/ci_build.sh                           |  11 +-
 11 files changed, 293 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-focal.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

-- 
2.30.1