RFE: Add hook to skip all cleaning on specific block device to HardwareManager

[Daniel King]

It may occur that a user with a custom hardware manager may wish to programmatically reject all cleaning on a specific block device, including the metadata, at runtime rather than by specifying it in properties.skip_block_devices as a device hint. For instance, a user might wish to check for any drives which contain an lvm and a volume group of a specific name, or they might wish to look for certain files or backups on a server with multiple disks and choose that those block devices should not be cleaned.

Currently, there is already the expectation that a user may wish to skip devices based upon skip_block_devices, which is retrieved from HardwareManager.get_skip_list_from_node(). Unfortunately, this presumes that the user knows ahead of time a device hint which will target the desired nodes. It does not allow for custom checks.

What I am proposing is some sort of hook, and abstract member of HardwareManager, which is called using dispatch_to_managers which can allow specific block devices to not be cleaned.

An example of how this might be done is to extend the functionality already being used by HardwareManager.get_skip_list_from_node(). It would be good to leave that code as is, but create a wrapper function HardwareManager.get_skip_list(self, node, block_devices=None, just_raids=False), which is used in each place where get_skip_list_from_node is called. That new method then calls get_skip_list_from_node to collect its skip_list, but additionally combines the output of a call to dispatch_to_managers to load another new method, get_additional_skip_list(self, node, block_devices=None), which is a new abstract method in HardwareManager returning IncompatibleHardwareMethodError, and the GenericHardwareManager could implement it to return an empty skip_list.

The result would be that new custom HardwareManager classes could add a method get_additional_skip_list to run their own custom code to check the list of devices, and if any are desired to be skipped, they could return them in an array.

[Jay Faulkner (jason-oldos)]

RFE approved during Ironic meeting here: https://meetings.opendev.org/irclogs/%23openstack-ironic/%23openstack-ironic.2024-03-25.log.html#t2024-03-25T15:42:33

Some notes:
- Please ensure a detailed release note comes with the patch
- Please create a new example hardware manager providing a usage example with comments