Add SONiC development docs (#50)

Signed-off-by: Matej Feder <[email protected]>

documentation/sonic/Build.md

@@ -4,20 +4,20 @@ This guide provides step-by-step instructions to build a SONiC image, particular
 
 ## Prerequisites
 
-### Hardware Requirements
+### Hardware requirements
 
 - **CPU**: Minimum 8 cores (more cores for faster builds)
 - **RAM**: Minimum 8 GB, recommended 32 GB
 - **Storage**: At least 300 GB of free disk space
 - **KVM Virtualization Support**: Required for build of VS (virtual switch) platform
 
-### Software Requirements
+### Software requirements
 
 - **Operating System**: Ubuntu 20.04 LTS is recommended
 - **Python 3**: Install via package manager
 - **Docker**: SONiC builds run in Docker containers
 
-### Set Up Environment
+### Set up environment
 
 - Install Required Packages
    ```bash

documentation/sonic/Development.md

@@ -0,0 +1,103 @@
+# SONiC development
+
+To develop on SONiC NOS efficiently, here are the key steps and techniques compiled from various sources.
+
+The SONiC packages often depend on several other packages, some available on PyPI and others within the SONiC codebase.
+To properly build or test SONiC packages, you must install these dependencies manually or let the SONiC build system
+handle the setup. SONiC build system configures a complete environment with all dependencies inside a Docker container.
+
+## Prerequisites
+
+Follow and apply instructions [here](Build.md#prerequisites).
+
+## Development
+
+From the sonic-buildimage directory...
+
+- Checkout a specific branch of `sonic-buildimage` repository. By default, the `master` branch is used, it may be a good idea to
+  develop against this branch. Ensure `master` branch:
+  ```bash
+  git checkout master
+  ```
+- Initialize the build environment
+  ```bash
+  make init
+  ```
+- Execute make configure once to configure ASIC (this may take a while). See full list of supported vendors [here](https://github.com/sonic-net/sonic-buildimage?tab=readme-ov-file#usage).
+  You can use `vm` if you want to test your feature/fix in the virtual switch environment, or you can also use `generic`
+  platform as a placeholder:
+  ```bash
+  make configure PLATFORM=vm
+  ```
+- List build targets to get a list of available `.deb` (debian package) and `.whl` (python wheel) targets
+  for different SONiC components, like `sonic_frr_mgmt_framework` or other platform-specific targets.
+  ```bash
+  $make list
+  ...
+  target/debs/bookworm/sonic-platform-vs_1.0_amd64.deb
+  target/debs/bookworm/sonic-dhcp6relay-dbgsym_1.0.0-0_amd64.deb
+  target/debs/bookworm/sonic-eventd-dbgsym_1.0.0-0_amd64.deb
+  target/debs/bookworm/sonic-rsyslog-plugin_1.0.0-0_amd64.deb
+  target/debs/bookworm/iccpd-dbg_0.0.5_amd64.deb
+  target/debs/bookworm/ipmitool-dbgsym_1.8.19-4+deb12u1_amd64.deb
+  ...
+  target/python-wheels/bookworm/sonic_containercfgd-1.0-py3-none-any.whl
+  target/python-wheels/bookworm/sonic_ctrmgrd-1.0.0-py3-none-any.whl
+  target/python-wheels/bookworm/sonic_dhcp_utilities-1.0-py3-none-any.whl
+  target/python-wheels/bookworm/sonic_frr_mgmt_framework-1.0-py3-none-any.whl
+  target/python-wheels/bookworm/sonic_utilities-1.2-py3-none-any.whl
+  ...
+  ```
+
+- Build the target package, e.g. `sonic_frr_mgmt_framework` python wheel package, within the debian bookworm slave container.
+  Instruct the system to keep the container running after the build completes:
+  ```bash
+  make -f Makefile.work BLDENV=bookworm KEEP_SLAVE_ON=yes target/python-wheels/bookworm/sonic_frr_mgmt_framework-1.0-py3-none-any.whl
+  ```
+  - If the make command immediately finishes with the message "Nothing to do, the package is up-to-date", it indicates
+    that the package has already been built during a previous image build and is up to date. In this case, simply remove
+    the package and proceed:
+    ```bash
+    rm target/python-wheels/bookworm/sonic_frr_mgmt_framework-1.0-py3-none-any.whl
+    ```
+- When the build finishes, your prompt will change to indicate you are inside the slave container. Change into the package directory:
+  ```bash
+  user@58b655f15722:/sonic$ cd src/sonic-utilities/
+  ```
+- Now that you are in the development environment, you can start editing the package source code, build it, or run its unit
+  tests. 
+  - You can edit files on your local, as your local `sonic-buildimage` clone is mounted to `/sonic` directory in the
+    slave container. Validate slave container mounts as follows (from your local): 
+    ```bash
+    $ docker ps | grep sonic
+    58b655f15722   sonic-slave-bookworm-user:c243baccce2   "bash -c 'make -f sl…"   7 minutes ago   Up 7 minutes       22/tcp    peaceful_darwin
+    $ docker inspect -f '{{ .Mounts }}' 58b655f15722
+    ```
+  - Most unit tests in SONiC use the pytest framework. To run tests, use
+  ```bash
+  python3 setup.py test
+  ```  
+  - To build the python package after making changes (to specify the destination for the built package, use the -d option):
+  ```bash
+  python3 setup.py bdist_wheel # -d /desired/output/location
+  ```
+
+## Deploying the developed package on a SONiC device
+
+Obviously, when developing, it is quite inefficient to build the whole SONiC image each time and then do a full installation of it.
+We can choose not to install the image and use the direct upgrade of newly developed package to do a partial upgrade,
+thus improving our development efficiency.
+To do this, upload the new package to the `/etc/sonic` directory of the switch, which will automatically map to the 
+`/etc/sonic` directory inside all containers. Then, enter the relevant container and use the suitable command to install
+the package:
+
+```bash
+# Enter the docker container inside SONiC switch
+docker exec -it <container> bash
+# Install the package
+# For .deb package:
+dpkg -i <deb-package>
+# For python package (note: Don't use "--force-reinstall"): 
+sudo pip uninstall YOUR_WHEEL_PACKAGE
+sudo pip install YOUR_WHEEL_PACKAGE 
+```