Version: nanbield

Building SDKs

SDK for Erlang and Elixir

The meta-erlang layers includes the possibility to generate development toolchains enabling better and smooth experience for the developer.

One could easily generates a specific SDK with all tools and libraries needed. For example: if your project needs Erlang 22.1.8 and Elixir 1.10, you can generate a SDK having these two dependencies. Then all the developers can share and use the same SDK during the development phase.

In order to use a specific Erlang and Elixir versions, configure the following variables in the file conf/local.conf or in the distro configuration file:

PREFERRED_VERSION_erlang = "23.0.4"
PREFERRED_VERSION_erlang-native = "23.0.4"
PREFERRED_VERSION_nativesdk-erlang = "23.0.4"

PREFERRED_VERSION_elixir = "1.11.2"
PREFERRED_VERSION_elixir-native = "1.11.2"
PREFERRED_VERSION_nativesdk-elixir = "1.11.2"

info

The default PACKAGECONFIG for erlang when nativesdk is to enable wx and observer tools. And if your distribution configuration disables (or removes) the opengl configuration, you will need to add opengl in DISTRO_FEATURES_NATIVESDK variable (in or local.conf for instance). Like this:

DISTRO_FEATURES_NATIVESDK:append = " opengl"

Maybe your team have special version of Erlang or Elixir with some in-house patches, using a SDK created by YP is a good approach to follow. You will have total control from the build until development SDK installation.

Also the SDK have all the dependencies to cross compile applications for target hardware. So the developer has just one installation to perform in order to access all the tools.

The recipe meta-erlang-toolchain is the main entry point when creating a generic toolchain with Erlang and Elixir. And comes with Erlang, Elixir development modules as well rebar3 build tool.

note

The follow two sections are based on Yocto Project Application Development and the Extensible Software Development Kit (eSDK) for Yocto Project 3.1.3 LTS "Dunfell". To get an up-to-date documentation, please, visit the Yocto Project Documentation

Standard SDK

Using the Standard SDK is simple as:

bitbake meta-erlang-toolchain

After finishing the SDK generation command, check the YP TMPDIR. A new file has been created like this: poky-glibc-x86_64-meta-erlang-toolchain-armv7vet2hf-neon-qemuarm-toolchain-3.1.3.sh. The file name depends on many factors like machine configuration and YP version.

The next step is run the toolchain installation script, like this:

~/work/opensource/build/tmp/deploy/sdk/poky-glibc-x86_64-meta-erlang-toolchain-armv7vet2hf-neon-qemuarm-toolchain-3.1.3.sh
Poky (Yocto Project Reference Distro) SDK installer version 3.1.3
=================================================================
Enter target directory for SDK (default: /opt/poky/3.1.3): /opt/poky/3.1.3
You are about to install the SDK to "/opt/poky/3.1.3". Proceed [Y/n]?
Extracting SDK.............................................done
Setting it up...done
SDK has been successfully set up and is ready to be used.
Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
 $ . /opt/poky/3.1.3/environment-setup-armv7vet2hf-neon-poky-linux-gnueabi

As the last sentence says, just source the file environment-setup-armv7vet2hf-neon-poky-linux-gnueabi and we ready to use Erlang and Elixir.

tip

If you need to customize the toolchain, i.e: add or remove tools, YP supports customize the Standard SDK.

Extensible SDK

Extensible SDK is the newly way in order to create SDK with YP. It includes the devtool tool to help the development workflow when working with new recipes or testing with the target hardware.

The instructions for generating an eSDK is as follow:

bitbake core-image-minimal -c populate_sdk_ext

The populate_sdk_ext works only with image recipes. After finishing the command, it is time to install the SDK like this:

joaohf@porco:~/tmp/poky$ ~/work/opensource/build/tmp/deploy/sdk/poky-glibc-x86_64-core-image-minimal-armv7vet2hf-neon-qemuarm-toolchain-ext-3.1.3.sh
Poky (Yocto Project Reference Distro) Extensible SDK installer version 3.1.3
============================================================================
Enter target directory for SDK (default: ~/poky_sdk):
You are about to install the SDK to "/home/joaohf/poky_sdk". Proceed [Y/n]?
Extracting SDK..................................................done
Setting it up...
Extracting buildtools...
Preparing build system...
WARNING: /home/joaohf/poky_sdk/layers/poky/meta-axon/recipes-support/glfw/glfw_3.2.1.bb: distro_features_check.bbclass is deprecated, please use features_check.bbclass instead
Parsing recipes: 100% |#########################################################################################################################################| Time: 0:02:14
Initialising tasks: 100% |######################################################################################################################################| Time: 0:00:01
Loading cache: 100% |###########################################################################################################################################| Time: 0:00:00
Initialising tasks: 100% |######################################################################################################################################| Time: 0:00:00
done
SDK has been successfully set up and is ready to be used.
Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
 $ . /home/joaohf/poky_sdk/environment-setup-armv7vet2hf-neon-poky-linux-gnueabi

Source the environment setup script for each new shell session that you want to use the SDK.

tip

Additional tools can also be included if needed, checkout the Customizing the Extensible SDK documentation.

Development session example

This section shows an example about how to use the SDK during a development session and exploring how we can use the command devtool to help fixing a bug in an Erlang application.

We are going to perform the following steps:

created a new bitbake recipe for an Erlang application
build the recipe
create an image and run it using QEMU
execute the Erlang application on QEMU
make a change in the application and use hot code swapping to change the application, that is, without stop the running application or restart the QEMU machine
clean up the target QEMU
finish up the recipe

One can use the same approach when working with a real hardware.

note

This session is far from be generic steps in order to develop, build, test and deploy Erlang/Elixir projects using Yocto Project. The purpose here is just to demonstrate one of multiple workflows.

Let's start loading the SDK setup environment:

$ cd ~/poky_sdk
$ source environment-setup-armv7vet2hf-neon-poky-linux-gnueabi
SDK environment now set up; additionally you may now run devtool to perform development tasks.
Run devtool --help for further details.

For this experience we are going to use a small Erlang application called elock. Clone it and build using rebar3 build tool.

$ git clone https://github.com/joaohf/elock
$ cd elock
$ rebar3 compile

Alright, the SDK is working as expected. The rebar3 tool is included into the SDK as well all the Erlang development requirements. The next step is create an elock bitbake recipe.

Still in the elock folder, call the devtool add in order to create a standard bitbake recipe:

$ devtool add elock .
NOTE: Starting bitbake server...
NOTE: Starting bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
NOTE: Reconnecting to bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
NOTE: Retrying server connection (#1)...
NOTE: Starting bitbake server...
INFO: Using source tree as build directory since that would be the default for this recipe
INFO: Recipe /home/joaohf/poky_sdk/workspace/recipes/elock/elock_git.bb has been automatically created; further editing may be required to make it fully functional

devtool created a new recipe call elock_git.bb. This recipe does not work because Yocto Project doesn't know how to read an Erlang/Elixir project and generate a proper bitbake recipe. So we need to use a rebar3 plugin called rebar3_bitbake which knows how to create a proper recipe:

$ rebar3 bitbake
$ cp elock_0.1.0.bb /home/joaohf/poky_sdk/workspace/recipes/elock/elock_git.bb

Now, elock recipe is ready. As the last step before the build, let's fix the recipe version because we want to build and release the version 0.1.0. So, still using devtool to change the recipe name do:

$ devtool rename -V 0.1.0 elock
NOTE: Starting bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:00
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:01
Parsing of 1943 .bb files complete (1937 cached, 6 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
INFO: Renaming /home/joaohf/poky_sdk/workspace/appends/elock_git.bbappend to /home/joaohf/poky_sdk/workspace/appends/elock_0.1.0.bbappend
INFO: Renaming /home/joaohf/poky_sdk/workspace/recipes/elock/elock_git.bb to /home/joaohf/poky_sdk/workspace/recipes/elock/elock_0.1.0.bb

Finally, call devtool to build the elock recipe like this:

$ devtool build elock
NOTE: Starting bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:00
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:00
Parsing of 1943 .bb files complete (1942 cached, 1 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:04
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:00
Parsing of 1943 .bb files complete (1942 cached, 1 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
NOTE: Resolving any missing task queue dependencies
Initialising tasks: 100% |#############################################################################################################################################| Time: 0:00:00
Sstate summary: Wanted 13 Found 1 Missed 12 Current 137 (7% match, 92% complete)
NOTE: Executing Tasks
NOTE: elock: compiling from external source tree /home/joaohf/work/projetos/elock
NOTE: Tasks Summary: Attempted 613 tasks of which 608 didn't need to be rerun and all succeeded.

Awesome, everything works. Now we need to build an image which has a working Linux distro made with Yocto Project:

$ devtool build-image core-image-minimal
NOTE: Starting bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:00
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:00
Parsing of 1943 .bb files complete (1942 cached, 1 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
INFO: Building image core-image-minimal with the following additional packages: elock
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:04
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:00
Parsing of 1943 .bb files complete (1941 cached, 2 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
NOTE: Resolving any missing task queue dependencies
Initialising tasks: 100% |#############################################################################################################################################| Time: 0:00:05
Sstate summary: Wanted 98 Found 1 Missed 97 Current 877 (1% match, 90% complete)
NOTE: Executing Tasks
NOTE: Tasks Summary: Attempted 2649 tasks of which 2423 didn't need to be rerun and all succeeded.
INFO: Successfully built core-image-minimal. You can find output files in /home/joaohf/poky_sdk/tmp/deploy/images/qemuarm

So far we build elock application as well the core-image-minimal. Now, it is time to running the image using qemu.

Open a new shell session and source again the SDK environment variables. This is necessary because QEMU will block the terminal.

$ cd ~/poky_sdk
$ source environment-setup-armv7vet2hf-neon-poky-linux-gnueabi

And then, start the QEMU:

$ devtool runqemu core-image-minimal

QEMU will start its booting process and we can connect over ssh to the IP address 192.168.7.2 using root as ssh user.

But our main aim now is to install the elock application into the QEMU instance. The core-image-minimal does not have the elock installed. So, let's install it right now calling devtool and the deploy-target subcommand, like this:

$ devtool deploy-target elock root@192.168.7.2
NOTE: Starting bitbake server...
NOTE: Reconnecting to bitbake server...
NOTE: Retrying server connection (#1)...
Loading cache: 100% |##################################################################################################################################################| Time: 0:00:00
Loaded 3037 entries from dependency cache.
Parsing recipes: 100% |################################################################################################################################################| Time: 0:00:00
Parsing of 1943 .bb files complete (1942 cached, 1 parsed). 3038 targets, 113 skipped, 0 masked, 0 errors.
INFO: Successfully deployed /home/joaohf/poky_sdk/tmp/work/armv7vet2hf-neon-poky-linux-gnueabi/elock/0.1.0-r0/image

elock has been installed, however it is not started yet. In order to start it for the first time, open a new terminal, connect over ssh and start elock application:

ssh root@192.168.7.2
root@qemuarm:~# cd /usr/lib/elock/bin
root@qemuarm:/usr/lib/elock/bin# ./elock
Erlang/OTP 23 [erts-11.1.3] [source] [smp:1:1] [ds:1:1:10] [async-threads:1]

=WARNING REPORT==== 20-Nov-2020::20:14:43.909058 ===
Setting Ranch options together with socket options is deprecated. Please use the new map syntax that allows specifying socket options separately from other options.

Eshell V11.1.3  (abort with ^G)
1>

Ok, elock is up and running. Back to the development terminal and let's test if elock is working:

$ ssh -p 4050 admin@192.168.7.2
The authenticity of host '[192.168.7.2]:4050 ([192.168.7.2]:4050)' can't be established.
RSA key fingerprint is SHA256:VXMXRo0wQnsCC5rFxuOy4rT3NSc5NLjoxvtcLpa0OFI.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '[192.168.7.2]:4050' (RSA) to the list of known hosts.
SSH server
Enter password for "admin"
password:
Enter command or `help`
elock> get_code
---> {ok,<<"12345">>}
elock> exit

Nice, it works! But, we want to change the default code from 12345 to 7777. What we are going to do is fix the default code, redeploy and verify if the hot swap code worked as expected:

Change the elock application like this:

diff --git a/src/elock_statem.erl b/src/elock_statem.erl
index fc0b10e..3f88dd4 100644
--- a/src/elock_statem.erl
+++ b/src/elock_statem.erl
@@ -24,7 +24,7 @@ get_timeout() ->
 set_timeout(Tmo) -> ok.

 get_code() ->
-    {ok, <<"12345">>}.
+    {ok, <<"77777">>}.

Build the recipe with the changes made.

$ devtool build elock

And deploy elock. The deploy-target subcommand will take care about copying the files to the target directory.

$ devtool deploy-target elock root@192.168.7.2

Switch to the ssh session and load the elock_statem code using code:load_file/1. This is the most basic way to perform hot code swapping.

code:load_file(elock_statem).
{module,elock_statem}

Now, it is time to connect again over ssh 4050 port and check if the new pass code takes effect:

$ ssh -p 4050 admin@192.168.7.2
The authenticity of host '[192.168.7.2]:4050 ([192.168.7.2]:4050)' can't be established.
RSA key fingerprint is SHA256:VXMXRo0wQnsCC5rFxuOy4rT3NSc5NLjoxvtcLpa0OFI.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '[192.168.7.2]:4050' (RSA) to the list of known hosts.
SSH server
Enter password for "admin"
password:
Enter command or `help`
elock> get_code
---> {ok,<<"77777">>}

It works! We are very very happy with all these changes. Time to clean up the target hardware, that is, remove the elock files (this is not strict necessary, but just to show that it is possible):

$ devtool undeploy-target elock root@192.168.7.2

Now, the last step is to finish up all the recipe changes. The subcommand finish creates any patches corresponding to commits in the local repository, moves the new recipe to a specific layer and resets the recipe moving it from the workspace to the layer.

$ devtool finish -f elock meta-axon

Finally, just check the final recipe results: ~/poky_sdk/layers/poky/meta-axon/recipes-elock/elock/elock_0.1.0.bb

All done. We've created a recipe, change the Erlang application, deployed it on the target hardware, applied a fix using hot code swapping without stopping the application, checked the fix and finished up the recipe changes.

Building SDKs

SDK for Erlang and Elixir​

Standard SDK​

Extensible SDK​

Development session example​

SDK for Erlang and Elixir

Standard SDK

Extensible SDK

Development session example