OHOS build environment setup proposal

Draft of ADR concerning OHOS build environment setup

Signed-off-by: Robert Drab <robert.drab@huawei.com>

adr/0001-ohos-environment-setup.md

+OHOS environment setup for different kernels
+============================================
+
+Given that OHOS will run on multiple different kernels we need 
+a straight-forward way of setting up build environment.
+There are many possible solutions, so we need to pick a sensible one
+that'll suit our needs.
+
+## Configuration / adaptation layers for kernels withing meta-openharmony
+
+One option is to make configuration / adaptaion layer per kernel which
+will contain all necessary bitbake configs (e.g. local.conf.sample,
+bblayers.conf.sample, etc.) that can be used together with oe-init-build-env
+script:
+
+    TEMPLATECONF=meta-openharmony/meta-ohos-zephyr/conf . oe-init-build-env
+
+This will create a build/conf directory based on the contents of meta-ohos-zephyr/conf
+where all required layers and configs can be defined. The same applise for other
+kernels, like FreeRTOS, Liteos or any other Linux-based distro.
+
+Below is a sequence diagram of how this could look like for Zephyr: 
+![ohos-zephyr-build-sequence-diagram](../diagrams/0001-meta-openharmony-zephyr-build-sequence-diagram.svg)
+

diagrams/0001-meta-ohos-zephyr-build-seqence.puml

+@startuml 0001-meta-openharmony-zephyr-build-sequence-diagram
+!includeurl https://raw.githubusercontent.com/RicardoNiepel/C4-PlantUML/release/1-0/C4_Container.puml
+
+LAYOUT_AS_SKETCH()
+
+Person(dev, "Developer", "Anyone willing to build the OHOS based image")
+System_Boundary(meta_openharmonyn, "meta-openharmony") {
+    Container(meta_ohos_zephyr, "meta-ohos-zephyr", "meta-layer", "OHOS configuration / adaptation layer for Zephyr")
+    Container(meta_ohos_poky, "meta-ohos-poky", "meta-layer", "OHOS configuration / adaptation layer for Poky")
+    Container(meta_ohos_init, "meta-ohos-init", "meta-layer", "OHOS initialisation services for application devices")
+    Container(meta_ohos_init_lite, "meta-ohos-init-lite", "meta-layer", "OHOS initialisation services for uC-based devices")
+    Container(meta_ohos_softbus, "meta-ohos-softbus", "meta-layer", "OHOS softbus service for application devices")
+    Container(meta_ohos_softbus_lite, "meta-ohos-softbus-lite", "meta-layer", "OHOS softbus service for uC-based devices")
+}
+Container(meta_zephyr, "meta-zephyr", "meta-layer", "ZephyrOS meta-layer")
+System_Ext(yocto, "yocto-poky", "distro scaffolding: predefined meta-data, bitbake build system")
+
+Rel(dev, meta_ohos_zephyr, "1. selects OHOS Zephyr distribution", "environment shell script")
+Rel(meta_ohos_zephyr, yocto, "2. sets up bitbake environment for OHOS Zephyr", "local.conf.sample, bblayers.conf.sample")
+Rel(dev, yocto, "3. initiates the build", "bitbake")
+Rel(yocto, meta_ohos_init_lite, "4. incorporates Zephyr-compatible OHOS layers")
+Rel(yocto, meta_ohos_softbus_lite, "4. incorporates Zephyr-compatible OHOS layers")
+Rel(yocto, meta_zephyr, "4. incorporates")
+
+Lay_D(dev, yocto)
+Lay_D(dev, meta_openharmonyn)
+Lay_D(meta_ohos_zephyr, meta_ohos_init_lite)
+Lay_D(meta_ohos_init_lite, meta_ohos_softbus_lite)
+Lay_D(meta_zephyr, yocto)
+@enduml
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