Great!

ccache might just require a little bit of extra set up. We have something similar for p4c:
https://github.com/p4lang/p4c/blob/main/.github/workflows/disabled/ci-ubuntu-18-nightly.yml#L41

You may also have to set the directory: https://github.com/p4lang/p4c/blob/main/tools/ci-build.sh#L133

Also, please sign the DCO:
https://github.com/p4lang/p4c/blob/main/CONTRIBUTING.md#contributing-license

The current workflow for p4c (https://github.com/p4lang/p4c/blob/main/.github/workflows/ci-container-image.yml) uses the Dockerx build step which differs from the one you mentioned in https://github.com/p4lang/p4c/blob/main/.github/workflows/disabled/ci-ubuntu-18-nightly.yml#L41.
To get it to work with Dockerx building, I now mount a cache volume for ccache to the Docker image which should work without the need for the export_ccache.sh script.

However, the cache hit rate seems marginal:

 #14 7068.5 Summary:
#14 7068.5   Hits:               84 /  6185 (1.36 %)
#14 7068.5     Direct:           59 /  6254 (0.94 %)
#14 7068.5     Preprocessed:     25 /  6173 (0.40 %)
#14 7068.5   Misses:           6101
#14 7068.5     Direct:         6195
#14 7068.5     Preprocessed:   6148
#14 7068.5   Uncacheable:      1099
#14 7068.5 Primary storage:
#14 7068.5   Hits:              143 / 12485 (1.15 %)
#14 7068.5   Misses:          12342
#14 7068.5   Cache size (GB):  0.40 /  5.00 (7.97 %)

The DCO verifier should be happy now.

EDIT: Seems that #98 has broken something for the Docker CI:

#14 5437.4 [ 35%] Generating bf_kdrv.ko
#14 5437.4 make[3]: *** modules: No such file or directory.  Stop.
#14 5437.4 make[2]: *** [pkgsrc/bf-drivers/kdrv/bf_kdrv/CMakeFiles/bf_kdrv.dir/build.make:76: pkgsrc/bf-drivers/kdrv/bf_kdrv/bf_kdrv.ko] Error 2
#14 5437.4 make[1]: *** [CMakeFiles/Makefile2:7197: pkgsrc/bf-drivers/kdrv/bf_kdrv/CMakeFiles/bf_kdrv.dir/all] Error 2
#14 5437.4 make[1]: *** Waiting for unfinished jobs....
#14 5437.4 [ 35%] Building C object pkgsrc/bf-drivers/src/dru_sim/CMakeFiles/dru_model.dir/dru_intf_tcp.c.o
#14 5437.4 [ 35%] Building C object pkgsrc/bf-drivers/src/dru_sim/CMakeFiles/dru_model.dir/__/lld/lld_dr_regs_tof.c.o
#14 5437.4 [ 35%] Building C object pkgsrc/bf-drivers/src/dru_sim/CMakeFiles/dru_model.dir/__/lld/lld_dr_regs_tof2.c.o
#14 5437.4 [ 35%] Built target dru_sim_o
#14 5437.4 [ 35%] Building C object pkgsrc/bf-drivers/src/dru_sim/CMakeFiles/dru_model.dir/__/lld/lld_dr_regs_tof3.c.o
#14 5437.4 [ 35%] Building C object pkgsrc/bf-drivers/src/dru_sim/CMakeFiles/dru_model.dir/__/lld/lld_dr_regs.c.o
#14 5437.4 [ 35%] Linking C static library ../../../../../install/lib/libdru_model.a
#14 5437.4 [ 35%] Built target dru_model
#14 5437.4 make: *** [Makefile:156: all] Error 2
#14 5437.4   - libcrafter: Cmd 'make --jobs=4 install' took: 0:00:17.641680, status: 2
#14 5437.4 
#14 5437.4 For more details, see: /open-p4studio/p4studio/logs/p4studio_2025-06-25_10-27-33.log
#14 5437.4 Error: Installation completed unsuccessfully
#14 ERROR: process "/bin/sh -c ./p4studio/p4studio profile apply --jobs $(nproc) ./p4studio/profiles/docker.yaml &&     ccache -s" did not complete successfully: exit code: 1

Not sure why though... It works for the testing CI

The current workflow for p4c (https://github.com/p4lang/p4c/blob/main/.github/workflows/ci-container-image.yml) uses the Dockerx build step which differs from the one you mentioned in https://github.com/p4lang/p4c/blob/main/.github/workflows/disabled/ci-ubuntu-18-nightly.yml#L41.

Yes, for the container workflow in P4C we have the same problem that ccache does not work actually. For the Ubuntu 18.04 workflow things were working using the steps I provided. We can leave it for now and figure it out later, but it would be nice to make use of ccache. Otherwise the build will take a loooong time.

EDIT: Seems that #98 has broken something for the Docker CI:

This step builds a kernel module. Possible that these folders are not mapped in Docker?

Alright, I will create an issue later so that the ccache feature for the docker CI does not fall into oblivion :) Should I also remove all ccache related parts for now?

Yes, it seems that this is the problem, and building kernel modules in Docker does not look that straightforward. Is there a configuration flag or environment variable that we could set to disable kernel module building?

Is there a configuration flag or environment variable that we could set to disable kernel module building?

Yes, there should be an option in the CMakelists to build kernel modules, You can toggle that.

Feel free to create the issue and remove the ccache changes. Maybe add them to the issue for the future.

Is there a configuration flag or environment variable that we could set to disable kernel module building?

Yes, there should be an option in the CMakelists to build kernel modules, You can toggle that.

I tried to set it with CMAKE_ARGS="-DKERNEL-MODULES=OFF" ./p4studio/p4studio profile apply --jobs $(nproc) ./p4studio/profiles/docker.yaml and CMAKE_FLAGS without success. I now simply added a sed replace to the Dockerfile.

Is there a configuration flag or environment variable that we could set to disable kernel module building?

Yes, there should be an option in the CMakelists to build kernel modules, You can toggle that.

I tried to set it with CMAKE_ARGS="-DKERNEL-MODULES=OFF" ./p4studio/p4studio profile apply --jobs $(nproc) ./p4studio/profiles/docker.yaml and CMAKE_FLAGS without success. I now simply added a sed replace to the Dockerfile.

There is a way to pass CMake args to the studio build, or use the configuration file to pass the CMake arguments. But I do not quite remember how. I would need to check.

If passing this option does not work its a bug. Let's not use the sed hack.

@fruffy , @n1tr0-5urf3r !

Sorry for chiming in late, but if you are using p4studio tool to build open-p4studio (and I think that this is the right approach, since that's what others will use anyway), then p4studio's profiles have a standard parameter that turns building the kernel modules on or off.

Here is a trivial profile for your reference:

global-options: {}
features:
  drivers:
    kernel-modules: true
  p4-examples:
  - p4-16-programs
architectures:
- tofino

You can set this kernel-modules: parameter to true or false and be done in no time.

You can set this kernel-modules: parameter to true or false and be done in no time.

Thank you @vgurevich, this was exactly what I was looking for! I further added the kernel-modules flag to p4studio/profiles/README.md for documentation.