feat: add support for passing extra arguments to the SPICE viewer

[lvillani]

Description

This PR adds support for passing additional arguments to the SPICE viewer. The feature was added mainly to support passing --spice-usbredir-redirect-on-connect in order to support automatic USB device redirection. For example (in a configuration file):

viewer_extra_args="--spice-usbredir-redirect-on-connect=-1,0x1234,0x5678,-1,1"

Where 0x1234 and 0x5678 are example USB VID and PID, respectively.

The string format is described at https://www.spice-space.org/usbredir.html#filter-string-format.

This PR also contains a minor style commit (removing trailing whitespace) and another commit clarifying that "viewer" actually refers to the SPICE viewer.

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation (updates the documentation)

Checklist:

• I have performed a self-review of my code
• I have tested my code in common scenarios and confirmed there are no regressions
• I have added comments to my code, particularly in hard-to-understand sections
• I have made corresponding changes to the documentation

[cubic-dev-ai]

1 issue found across 2 files

Confidence score: 4/5

• Mild risk: in quickemu, --viewer-extra-args values containing spaces will be split in the desktop shortcut Exec line, which can break viewer invocation with multi-word args.
• This looks contained to shortcut generation and is a moderate usability issue rather than a core functionality break, so it seems safe to merge with awareness.
• Pay close attention to quickemu - quote or escape Exec line args to preserve spaces.

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="quickemu">

<violation number="1" location="quickemu:2720">
P2: `--viewer-extra-args` values containing spaces will break the generated desktop shortcut because the Exec line is not quoted, so additional viewer args are split into separate CLI options. Quote/escape the value when adding it to `SHORTCUT_OPTIONS` so it stays a single argument in the desktop file.</violation>
</file>

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[lvillani]

I updated commit messages to follow the current style a bit more closely (namely, I added the quickemu scope).

I'm a bit unsure about the remark from cubic since the feature is implemented nearly the same was as --extra-args.

[flexiondotorg]

@lvillani Thanks for contributing to the project 🙇 I've been reflecting on the growing number of arguments in quickemu. I'm planning to remove most of the advanced configuration from arguments and expose it exclusively through options in the VM configuration. This is to simplify the code a little and also focus the command execution on common use cases.

So, I won't be merging this pull request as it stands, but if you want to refactor it to be automatically enabled when appropriate or exposed only via a configuration option, I'd welcome that 👍

[lvillani]

Thanks for the feedback! I completely agree with the goal of simplifying the arguments and expose this setting only in the VM configuration file instead. I'll update the PR to implement it that way in a few days.

[lvillani]

I've updated the implementation so that viewer_extra_args is now exclusively read from the configuration file. I also realized I missed documenting this option in quickemu_conf.5.md earlier, so I've added that now.

I'm converting this PR to a draft while I perform more thorough testing. I'll mark it as ready for review once that's complete.

[lvillani]

I have rebased my branch against master and set the PR ready for review. I'm a bit unsure about the way I documented viewer_extra_args in quickemu_conf.5.md (I wrote an example of how I use the option to set-up automatic USB redirection even though the option is general-purpose).

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Small documentation updates (clarifying SPICE viewer) and minor feature addition (viewer_extra_args config option). 28 lines across 3 files. No destructive operations, credentials, or critical path a}

[lvillani]

Rebased against the master branch and fixed commit ordering. The build now appears to fail for reasons unrelated to this PR.

[lvillani]

@flexiondotorg Just bumping this since it's now ready for review! The changes reflect your feedback to move this directly to the VM configuration. Let me know what you think.