#4534: Remove multi irq support for mmio devices

[andr3wy]

Changes

-Utilized Option instead of Vector to store IRQ lines for MMIO devices.
-Add test to test this.
-Update existing tests
...

Reason

Currently, Firecracker have an ability to create multiple irqs for MMIO devices; however, no more than one IRQ is ever used. Therefore, it was suggested to change this to use an Option instead of a vector of length 0 or 1.
...

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

• If a specific issue led to this PR, this PR closes the issue.
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this
  PR.
• API changes follow the Runbook for Firecracker API changes.
• User-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.
• New TODOs link to an issue.
• Commits meet
  contribution quality standards.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.31%. Comparing base (9104425) to head (65e0e84).

Files with missing lines	Patch %	Lines
src/vmm/src/device_manager/mmio.rs	91.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4601   +/-   ##
=======================================
  Coverage   84.31%   84.31%           
=======================================
  Files         249      249           
  Lines       27521    27516    -5     
=======================================
- Hits        23205    23201    -4     
+ Misses       4316     4315    -1     

Flag	Coverage Δ
5.10-c5n.metal	84.54% <100.00%> (-0.01%)	⬇️
5.10-m5n.metal	84.52% <100.00%> (-0.01%)	⬇️
5.10-m6a.metal	83.81% <100.00%> (+<0.01%)	⬆️
5.10-m6g.metal	80.89% <90.00%> (-0.01%)	⬇️
5.10-m6i.metal	84.52% <100.00%> (+<0.01%)	⬆️
5.10-m7g.metal	80.89% <90.00%> (-0.01%)	⬇️
6.1-c5n.metal	84.54% <100.00%> (?)
6.1-m5n.metal	84.52% <100.00%> (?)
6.1-m6a.metal	83.81% <100.00%> (?)
6.1-m6g.metal	80.89% <90.00%> (?)
6.1-m6i.metal	84.51% <100.00%> (?)
6.1-m7g.metal	80.89% <90.00%> (?)

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[roypat]

Hi @andr3wy,
Thanks for your PR! There's a couple formatting and build issues on ARM that'll need to be fixed (see https://buildkite.com/firecracker/firecracker-pr/builds/9851 for what exactly is failing). For the formatting, you can run ./tools/devtool fmt to fix it up (and to check that the style checks will all pass, you can run ./tools/devtool checkstyle). For the build error on ARM, you can do cargo check --target aarch64-unknown-linux-gnu. That should allow you to validate the build without needing a cross-compilation toolchain. Also, please squash all the commits into a single one, and give it a meaningful description. Thanks!

[andr3wy]

Issues should be resolved.

[roypat]

Thanks for squashing the commits! It seems that a rebase went a bit awry though, your branch now has some commits that are already on main :( Could you drop those, so that only your commit remains part of this PR? Also, please add a commit body message - it's required for the style CI step to pass - just rephrasing the what you put under "Reason" in the PR description will be fine :).

Also I think there's still a compilation issue on ARM, could you have a look at that, too?

[andr3wy]

Wanted to write that I won't have access to a computer for at least a month (out of town), so this will have to be on the back burner for a while.

[JonathanWoollett-Light]

Related to #4534

[roypat]

Wanted to write that I won't have access to a computer for at least a month (out of town), so this will have to be on the back burner for a while.

Hi @andr3wy,
are you still interested in working on this?

[roypat]

Hi @andr3wy,
I've gone ahead and rebased the PR, and fixed the remaining outstanding compiler warnings. Thanks again for your contribution here!