Introduce environmental variable handling to kraft build and kraft run

[nderjung]

Feature request summary

This issue tracks allowing the parsing and passing of environmental variables from kraft build and kraft run via the command-line flag -e flag and an env element in the Kraftfile specification such that these key-values are correctly passed into posix-environ

• In the case of kraft build, these can be statically set at compile-time such that these variables are persistent with the unikernel.

• In the case of kraft run, they are passed via uklibparam via the syntax and requiring the KConfig option CONFIG_LIBPOSIX_ENVIRON_LIBPARAM:

  env.vars=[ "${NAME0}=${VALUE0}" "${NAME1}=${VALUE1}" ]
  

When no key is provided, for example kraft run -e HOME, the value should be automatically determined from the host environment via os.Getenv.

A new wrapper library should be introduced in unikraft/export/v0/posix-environ to accommodate handling the list of key-value environmental variables and the correct format to be used when instantiating the VM.

To statically serialize environmental variables, a new top-level env element should be added to the Kraftfile specification such that these are passed in the same way to kraft build and kraft run.

Map form:

spec: v0.6

env:
  KEY: value

List form:

spec: v0.6

env:
- KEY=value

Describe alternatives

No response

Related architectures

None

Related platforms

None

Additional context

See posix-environ: Handling Environmental Variables for additional details.

[LucaSeri]

Is anyone working on this at the moment? If not, can you please assign it to me?

[nderjung]

@LucaSeri 🪄

[nderjung]

@LucaSeri can you also introduce packmanager.PackWithEnv(env ...string) and inject the environmental variables into the ocispec.ImageConfig object?

See:

• Somewhere around here https://github.com/unikraft/kraftkit/blob/staging/oci/pack.go#L239
• https://github.com/unikraft/kraftkit/blob/staging/oci/manifest.go#L210 (New method similar to this, SetEnv(...string))
• https://github.com/opencontainers/image-spec/blob/v1.1.0/specs-go/v1/config.go#L32

Please & thank you! :)

[nderjung]

This draft PR may be interesting for you too see all the bits that need touching: #1286