Genode: Running out of capabilities on 64-bit platforms

27 Sep 2021

I am using Genode(with seL4) as the OS platform for demonstrating my research ideas. As with starting with a new platform I have run into some hurdles.

Running the hello_tutorial

The hello_tutorial job on QEMU did not finish to completing and timed out. Below are my steps on Ubuntu 20.04.1. I am using the Genode development container, so the tools should not an issue. I also tried it outside the container, with the same result.

git clone git:// 
cd genode
tool/ports/prepare_port sel4
tool/ports/prepare_port grub2
tool/create_builddir x86_64
cd x86_64/build/
# Change build/x86_64/etc/build.conf. 
# Change kernel to sel4 and add hello_tutorial
diff etc/build.conf.old etc/build.conf
< #KERNEL ?= nova
> KERNEL ?= sel4
> REPOSITORIES += $(GENODE_DIR)/repos/hello_tutorial

make hello
make run/hello 

This times out as shown below.

[init -> hello_server] creating root component [0m [0m
[init -> hello_client] upgrading quota donation for PD session (0 bytes, 4 caps) [0m [0m
[init] child "hello_server" requests resources: cap_quota=3 [0m [0m
[init] child "hello_client" requests resources: ram_quota=0, cap_quota=4 [0m [0m
Error: Test execution timed out

Response from Genode Dev

Thanksfully the Genode Mailing List was able to help out!!

They were able to reproduce the issue and pointed out that the issue is related to the used platform. As the log output states “hello_server” is requesting more resources and requires cap_quota (capability quota) increased during an operation that requires 3 caps. A look into the init configuration (see reveals the following.

<!-- all components get 50 capabilities per default -->
<default caps="50"/>

Now you may grant the component some more caps to make it run successfully by changing to the hello_server start node and running

<start name="hello_server" caps="54">
make run/hello KERNEL=sel4

This results in additional resource requests

[init] child "hello_server" requests resources: ram_quota=0, cap_quota=4

The reason is that the seL4 platforms works quite different from NOVA and expectedly Linux, which results in a higher capability consumption of the used software stack.

The following start nodes render the scenario working again.

<start name="hello_server" caps="58">
<start name="hello_client" caps="51">

Please see Chapters “Resource trading” [1] and “Resource assignment” [2] in the Genode Foundations book for a thorough explanation.

[1] Genode: Resource Trading

[2] Genode: Resource Assignment