DAOS-19260 control: Add capability to format storage of specific engine

[tanabarr]

Add optional engine_idx parameter to StorageFormatReq to allow formatting
storage for a specific engine instance rather than all engines on a host.

Features: control

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is 'Allow format on specific engine instance'
Status is 'Open'
https://daosio.atlassian.net/browse/DAOS-19260

[daosbuild3]

Test stage Unit Test completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18604/1/testReport/

[knard38]

If the engine-idx default-value issue I raised is confirmed, I think it should be fixed before landing. It would also be good to add unit test coverage for the new --engine-idx feature.

[knard38]

From my understanding, using cmd.EngineIdx without cmd.Rank defined and cmd.Replace true makes no sense and can even lead to some unexpected behaviour. If I am correct, the same kind of consistency checking done for cmd.Rank should be done for cmd.EngineIdx:

if cmd.EngineIdx != nil && cmd.Rank == nil {
    return errors.New("--engine-idx option is only valid when used with --rank")
}

[knard38]

From my understanding, the MaxUint32 sentinel for "no filter, format all engines" is only ever set in control.StorageFormat() (src/control/lib/control/storage.go), after convert.Types() runs. Any other code path (such as auto-format) that builds a ctlpb.StorageFormatReq directly gets the Go zero value (0) for EngineIdx, which this check reads as "filter to engine 0 only".

From my investigation, latest version of protoc support "optional" field. Sadly, the version used by DAOS seems to not support such feature. Then, one solution could be to add a bool field engine_idx_enabled to the proto message StorageFormatReq and to update the code in the following way:

Suggested change

	if req.EngineIdx != ^uint32(0) {
	if req.Replace && req.EngineIdxEnabled {

We could also keep the sentinel solution but we will have to fix all the code using this protoc struct and setting the replace field to true.