krun: Parse libkrun flavor indicated in KRUN_VM_FILE

[tylerfanelli]

To support other libkrun flavors in the future, parse which flavor (and by extension, which handle) should be used before making any libkrun API calls past libkrun_create_ctx. The correct handle to be used can be determined before any other subsequent API calls.

cc @slp

Summary by Sourcery

Parse the KRUN_VM_FILE early to detect the requested libkrun flavor and select the appropriate handle before making further libkrun calls.

Enhancements:

• Extract libkrun_read_vm_config to separate JSON parsing of the VM configuration file.
• Introduce libkrun_configure_flavor to switch between standard and SEV libkrun based on the config file or presence of KRUN_SEV_FILE.
• Update libkrun_exec to invoke the new config parsing and flavor-selection steps prior to VM configuration.

[sourcery-ai]

Reviewer's Guide

This PR refactors VM configuration handling in krun to support multiple libkrun flavors by splitting VM config parsing from flavor selection and wiring the new steps into the execution path.

File-Level Changes

Change	Details	Files
Extract separate VM config reader	Introduce new libkrun_read_vm_config function Move file-reading, JSON parsing and early exit logic into it Adjust parse_json_file call and cleanup variables	src/libcrun/handlers/krun.c
Refactor existing VM configurator to take parsed tree	Change libkrun_configure_vm signature to accept yajl_val pointer Add check for NULL config_tree and return early Update JSON field lookups to use dereferenced tree	src/libcrun/handlers/krun.c
Add flavor detection and selection	New libkrun_configure_flavor reads “flavor” field and KRUN_SEV_FILE Determine whether to use SEV or vanilla handle/context Set kconf->handle, ctx_id and sev flag accordingly	src/libcrun/handlers/krun.c
Wire new config steps into exec path	Remove inline SEV detection block from libkrun_exec Call libkrun_read_vm_config then libkrun_configure_flavor Pass config_tree into libkrun_configure_vm and assign handle/ctx_id from kconf	src/libcrun/handlers/krun.c

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[sourcery-ai]

Hey @tylerfanelli - I've reviewed your changes - here's some feedback:

• Ensure that the parsed YAJL tree (config_tree) is freed (e.g., via yajl_tree_free) after use to avoid memory leaks.
• Avoid calling exit() in libkrun_configure_flavor—return an error code instead to keep error handling consistent and non-terminating within library functions.
• Extract the literal "sev" into a named constant (or enum) to avoid magic strings and make adding future flavors easier.

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[packit-as-a-service]

Ephemeral COPR build failed. @containers/packit-build please check.

[giuseppe]

when do we clean it up (yajl_tree_free (...))?

We exit early on errors so we don't really care in this case, but could we release it before krun_start_enter?

[tylerfanelli]

Thanks for pointing that out, I never did free config_tree. I've modified 13fcca9 to free config_tree before krun_start_enter.

[giuseppe]

LGTM

[slp]

LGTM