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Johannes Schlatow avatar

Goa - Test running applications on Sculpt

Since its first release, Goa allows test-running applications on the host. We recently added an alternative run target to Goa which enables executing a Goa application on a Sculpt system.

When developing applications with Goa, the binary-compatibility of Genode executables between Linux and microkernels allows for a hassle-free test-running on the host system. However, this often involves emulation or "black-hole-ing" of certain parts such as accessed file systems, ROM modules, or even GPU access. Moreover, we need to resort to other means for test-running applications on other CPU architectures.

What if Goa was able to transfer the run directory to a running Sculpt system and thereby execute a scenario on the remote system instead of the host system?

Luckily, we already added support for run-stage customisation in release 23.10 so that implementing such a feature came naturally. In this article, I am going to explain the underlying concept and show how it is used in practice.


Goa places all files required for running a scenario in the var/run/ directory. By transferring these files to the remote system, we are basically able to launch the scenario on that system. Since we already had a port of lighttpd and Josef recently enabled the mod_webdav module, I opted for using HTTP PUT for file upload. However, in order not to add unnecessary waiting times, we want to omit transferring files that are already present, hence we need a smarter synchronisation solution. The idea was to leverage the server-provided ETags. An HTTP ETag is some kind of server-specific fingerprint of a file. Using the last-known ETag of a file, a client is able to conditionally upload a file only if it has been changed on the remote side.

I implemented this idea in share/goa/lib/ The script stores the ETags of each file in a temporary directory. It always uploads the locally changed files and uses the conditional upload mechanism for unchanged files.

In addition to lighttpd, the remote Sculpt system runs a sub-init that reacts to changes to the config file from the synchronised run directory. Once all prerequisites are synchronised, starting a scenario on the remote system merely consists in uploading the config file. By deleting the config file from the remote system, the scenario is killed.

But how does Goa acquire the log output from the remotely running sub-system?

For this, I used the tcp_terminal component to provide the log output via telnet. Moreover, log output and reports are stored in the HTTP server's directory and are available via directory listing.

I implemented this concept in my goa_testbed project. A ready-to-use archive is available in my depot. The official Sculpt 24.04 image also comes with a goa testbed preset.

With these ingredients, adding the corresponding run target was pretty straightforward. As it turned out, it is much simpler than the default linux target which needs to instantiate additional components for emulating the required services. Since the service routings are controlled on the target system when launching the Goa testbed, the Goa-generated config merely needs to route all services to the parent. See goa help targets for more details.

Goa testbed project

Goa testbed preset


In order to run a Goa project on a remote Sculpt system, you first need to launch goa_testbed. This is either done by enabling the corresponding preset (since Sculpt 24.04) or by installing the package from my depot.

Note that the preset applies label rewriting for the Nic routes as follows so that the session requests from lighttpd and tcp_terminal are re-labelled "http" resp. "telnet":

 <service name="Nic" label_prefix="tcp_terminal">
   <child name="nic_router" label="telnet"/> </service>
 <service name="Nic" label_prefix="lighttpd">
   <child name="nic_router" label="http"/>   </service>
 <service name="Nic"> <!-- for test scenario -->
   <child name="nic_router"/>                </service>

With these label rewritings, you can add the following domains and policies to the Nic router's config (default since Sculpt 24.04):

 <policy label="http" domain="http"/>
 <domain name="http" interface="">
   <dhcp-server ip_first="" ip_last="" dns_config_from="uplink"/>
 <policy label="telnet" domain="telnet"/>
 <domain name="telnet" interface="">
   <dhcp-server ip_first="" ip_last="" dns_config_from="uplink"/>

Also make sure to add corresponding forwarding rules to the uplink domain (external access) and/or the default domain (access from within Linux VM):

 <domain ...>
   <tcp-forward port="80" domain="http" to=""/>
   <tcp-forward port="23" domain="telnet" to=""/>

Having prepared the target system, we can easily test run a Goa scenario by adding --target sculpt to Goa's command line and by specifying the IP address of the target system (see goa help targets for more details). Let's try the calculator app from the previous article:

 calculator> goa run --target sculpt --target-opt-sculpt-server «sculpt-ip»
 uploaded (remote change)
 uploaded config (local change)
 Connected to
 Escape character is '^]'.
 [init -> lomiri-calculator-app] libEGL debug: Native platform type: genode
 Expect: 'interact' received 'strg+c' and was cancelled
 deleted config

The app magically pops up on the target system and the log output is shown on the development system. When hitting ctrl+c, the config is deleted from the target system, which kills the app.

Note that I like to put the --target-opt-server-sculpt argument into my goarc file:

 set target_opt(sculpt-server) «sculpt-ip»


Edit 2024-06-04: Refer to preset in Sculpt 24.04.