Create layer

Layers are prepares by OEM. They are shared by services and extend their rootfs. The layer consists of filesystem tree (files, folders) and a metadata that describes layer's content. See layer format for details.

Create layer using Yocto build

AosCore Yocto meta layers provide mechanism to create and build layers automatically based on Yocto packages and recipes. AosCore meta-aos repo contains example layers recipes that can be used as reference for creating custom layers or can be used to extend services rootfs.

There are two types of layers: layers that depend only on host rootfs and layers that depend on other layer.

Create layer based on host rootfs

In your Yocto meta layer, create layer recipe with the following path recipes-aos-layers/your-layer-name/your-layer-name.bb. This recipe should have the following content:

SUMMARY = "Description of your layer"

require recipes-aos-layers/aos-base-layer/aos-base-layer.inc

AOS_LAYER_FEATURES += " \
    ...
"

AOS_LAYER_VERSION = "1.0.0"

• SUMMARY - add your layer description;
• AOS_LAYER_FEATURES - add list of Yocto recipes that have to be included into this layer;
• AOS_LAYER_VERSION - your layer version in Semantic Versioning format.

Except above variables the layer recipe should include base layer image:

require recipes-aos-layers/aos-base-layer/aos-base-layer.inc

The layer can be built using bitbake command:

bitbake your-layer-name

By default, your layer image will be located in default deploy directory in layers folder.

See aos-pylibs-layer for reference.

Create layer based on other layer

In your Yocto meta layer, create layer recipe with the following path recipes-aos-layers/your-layer-name/your-layer-name.bb. This recipe should have the following content:

SUMMARY = "Description of your layer"

AOS_PARENT_LAYER = "parent-layer-name"

require recipes-aos-layers/parent-layer-name/parent-layer-name.bb

AOS_LAYER_FEATURES += " \
    ...
"

AOS_LAYER_VERSION = "1.0.0"

• SUMMARY - add your layer description;
• AOS_PARENT_LAYER - add parent layer name;
• AOS_LAYER_FEATURES - add list of Yocto recipes that have to be included into this layer;
• AOS_LAYER_VERSION - your layer version in Semantic Versioning format.

Except above variables the layer recipe should include parent layer recipe:

require recipes-aos-layers/parent-layer-name/parent-layer-name.bb

The layer can be built using bitbake command:

bitbake your-layer-name

By default, your layer image will be located in default deploy directory in layers folder.

See aos-libvis-layer for reference.

Add new layer to Aos VM

Let's add new layer for Aos VM. For instance, your service requires python library matplotlib. Let's add this library as Aos layer.

Create aos-matplotlib-layer recipe

Create a recipe for this layer with the following path:

yocto/meta-aos-vm/meta-aos-vm-common/recipes-aos-layers/aos-matplotlib-layer/aos-matplotlib-layer.bb.

Add the following content to the layer recipe:

SUMMARY = "python matplotlib layer"

require recipes-aos-layers/aos-base-layer/aos-base-layer.inc

AOS_LAYER_FEATURES += " \
    python3-matplotlib \
"

AOS_LAYER_VERSION = "1.0.0"

We've added python3-matplotlib package to this layer using AOS_LAYER_FEATURES variable.

Add aos-matplotlib-layer to moulin configuration file

Aos VM uses moulin build system. To add newly created layer to the list of Aos VM layers, edit aos-vm.yaml layers section in the following way:

• add new layer image to target_images;
• add new layer target item to layers items.

Your layers section should look like:

  layers:
    builder:
      type: custom_script
      work_dir: "workdir"
      script: "../yocto/meta-aos/scripts/layer_builder.py"
      target_images:
        - "../output/layers/pylibs-layer.tar.gz"
        - "../output/layers/libvis-layer.tar.gz"
        - "../output/layers/matplotlib-layer.tar.gz"

      additional_deps:
        - "%{YOCTOS_WORK_DIR}/build-%{NODE_TYPE}/tmp/deploy/images/%{MACHINE}/%{AOS_BASE_IMAGE}-%{MACHINE}.rootfs.ext4"

      layers:
        yocto_dir: "../%{YOCTOS_WORK_DIR}"
        build_dir: "build-%{NODE_TYPE}"
        output_dir: "../output/layers"
        base_image: "aos-image-vm"
        items:
          pylibs-layer:
            target: "aos-pylibs-layer"

          libvis-layer:
            target: "aos-libvis-layer"

          matplotlib-layer:
            target: "aos-matplotlib-layer"

Build Aos VM layers

To generate Aos VM layers, configure build for main node:

moulin aos-vm.yaml --NODE_TYPE=main

And generate all specified in aos-vm.yaml layers:

ninja layers

As result, you should see all layers images in output/layers folder.

See meta-aos-vm README.md for details.

How to use layers you may find here