allow specifying custom cpu template inline in config json

[roypat]

When starting firecracker without the API server and configuring it through a config files, specifying a custom cpu template requires writing this cpu template into a separate json file, and then passing the path to this separate json file in the config json file. This is a bit silly, since everything is just json. So additionally allow just directly specifying the custom cpu template inside the config file.

Changes

...

Reason

...

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
• When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.93%. Comparing base (114c87f) to head (6a58dba).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5175      +/-   ##
==========================================
+ Coverage   82.87%   82.93%   +0.05%     
==========================================
  Files         250      250              
  Lines       26932    26936       +4     
==========================================
+ Hits        22321    22339      +18     
+ Misses       4611     4597      -14     

Flag	Coverage Δ
5.10-c5n.metal	83.37% <100.00%> (+<0.01%)	⬆️
5.10-m5n.metal	83.36% <100.00%> (+<0.01%)	⬆️
5.10-m6a.metal	82.58% <100.00%> (-0.01%)	⬇️
5.10-m6g.metal	79.19% <100.00%> (+<0.01%)	⬆️
5.10-m6i.metal	83.35% <100.00%> (-0.01%)	⬇️
5.10-m7a.metal-48xl	82.58% <100.00%> (?)
5.10-m7g.metal	79.19% <100.00%> (+<0.01%)	⬆️
5.10-m7i.metal-24xl	83.32% <100.00%> (?)
5.10-m7i.metal-48xl	83.32% <100.00%> (?)
5.10-m8g.metal-24xl	79.19% <100.00%> (?)
5.10-m8g.metal-48xl	79.19% <100.00%> (?)
6.1-c5n.metal	83.42% <100.00%> (+<0.01%)	⬆️
6.1-m5n.metal	83.41% <100.00%> (-0.01%)	⬇️
6.1-m6a.metal	82.63% <100.00%> (+<0.01%)	⬆️
6.1-m6g.metal	79.19% <100.00%> (+<0.01%)	⬆️
6.1-m6i.metal	83.40% <100.00%> (+<0.01%)	⬆️
6.1-m7a.metal-48xl	82.62% <100.00%> (?)
6.1-m7g.metal	79.19% <100.00%> (-0.01%)	⬇️
6.1-m7i.metal-24xl	83.42% <100.00%> (?)
6.1-m7i.metal-48xl	83.43% <100.00%> (?)
6.1-m8g.metal-24xl	79.18% <100.00%> (?)
6.1-m8g.metal-48xl	79.19% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[zulinx86]

If I remember correctly, the reason why we made such a decision is that we anticipated users don't want to have the very long CPU template definition for each machine configuration (i.e. if users have 10 different machine configs with the same CPU template, when they want to change a single bit of the CPU template, they will have to change all the machine config JSON files). So the design is not so silly. I believe accepting both must be better though :D

[roypat]

If I remember correctly, the reason why we made such a decision is that we anticipated users don't want to have the very long CPU template definition for each machine configuration (i.e. if users have 10 different machine configs with the same CPU template, when they want to change a single bit of the CPU template, they will have to change all the machine config JSON files). So the design is not so silly. I believe accepting both must be better though :D

Ah, that's fair - my usecase was more than I had a single CPU template that only needed to modify a single cpuid leaf, and so it was easier to just have it straight in there. What you're saying makes sense though, I shouldn't have judged so soon 😔