introducing maxSizeGigabyte rootDeviceHint field

[Rozzii]

User Story

Although the custom root device hint operator issue has been frozen #1159,
I believe introducing a single extra (non Ironic specific) disk size related root device hint type would be beneficial and it would fit logically among the existing options as minSizeGigabye option is already present.

Detailed Description

I would like to introduce the maxSizeGigabye integer field to the rootDeviceHint object and make it visible on the API.

In case both maxSizeGigabyte and minSizeGigabyte would be populated, then it would be up to the provisioner interface to decide how that is interpreted but for the default provisioner (Ironic) I would like to implement a logic that interprets this situation as a range specification and it would execute 1 extra check.

The extra check would be that minSizeGigabyte <= maxSizeGigabyte otherwise the hint[size] wouldn't be populated. I went for not populating hint[size] in case of the extra check fails because the current behavior is the same for all rootDeviceHints for Ironic .

With the introduction of a single Integer field a BMH root device hint could specify the max, the exact and a range of sizes in addition to the already existing min size.

Anything else you would like to add:

• I would like to add this change to the stabilized v1alpha1 as it is not a complex change.
• I am willing to implement the change.

[Miscellaneous information that will assist in solving the issue.]

A few references :

• v1beta1 proposal PR: BareMetalHost API v1beta1 metal3-docs#332
• how BMO handles the hints for Ironic: https://github.com/metal3-io/baremetal-operator/blob/main/pkg/provisioner/ironic/devicehints/devicehints.go
• related section of the CRD:

  baremetal-operator/config/crd/bases/metal3.io_baremetalhosts.yaml

  Line 435 in 5cb7696

  rootDeviceHints:

/cc @dtantsur @zaneb @hroyrh @elfosardo @kashifest
/kind feature

EDITS:

• Formatting
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[zaneb]

+1. Not having this is a giant pain, it turns out.
Please add the min<max check to the validation webhook also.

[Rozzii]

/triage accepted

[metal3-io-bot]

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/lifecycle stale

[Rozzii]

/remove-lifecycle stale
I am just slow, this is still on my list.

[Rozzii]

I have started to work on this

[Rozzii]

After discussion in the Ironic and Oslo.utils communities a new SPEC DSL operator was proposed https://review.opendev.org/c/openstack/oslo.utils/+/908289 that would be used in turn as a new root device hint operator thus
the range specification that was planned for this BMO ticket could be supported as planned:

In case both maxSizeGigabyte and minSizeGigabyte would be populated, 
then it would be up to the provisioner interface to decide how that is interpreted but for the default provisioner (Ironic)
I would like to implement a logic that interprets this situation as a range specification and it would execute 1 extra check.