feat: Support for creating volumes without a FS

[japokorn]

Currently whenever volume is created without fs_type specification, a filesystem of default type (i.e. xfs) is automatically put on it.
This change allows user to prevent FS creation by using "unformatted" value as a fs_type option. In the same manner it also allows to remove an existing FS. To be able to do that the safe mode has to be off.

Enhancement:

Reason:

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Issue Tracker Tickets (Jira or BZ if any):

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[richm]

Does this require storage_safe_mode: false? Seems kinda dangerous

[japokorn]

Yes, it does. In code the behavior extends the functionality of _reformat method which handles the safe_mode.
Still, fs_type: None 'creation' on empty device will work even with safe_mode on since it is a no-op.

I have added the safe_mode requirement into the commit message, worth mentioning there.

[richm]

What happens now if the fs_type is not specified? e.g. if you use

        storage_pools:
          - name: foo
            disks: "{{ unused_disks }}"
            volumes:
              - name: test1
                size: "{{ volume_size }}"

what happens? Does the role do nothing? Does it remove the fs? Does it create a volume with no fs?

What happens when a user has a playbook with the above, which was working and creating file systems with fs_type xfs, and they upgrade the storage role, and run the playbook again? The user expects that the behavior will not change - that is, it should create fs_type xfs. We cannot easily break that, especially if the default will be destructive, or will just silently fail.

I think a better option to avoid breaking the api is to use a special value for fs_type e.g. fs_type: NOFS which will create the volume with no fs, or remove the fs on an existing volume.

[japokorn]

Using None is in this case recognized and processed differently than when fs_type is not used at all.

For idempotency reasons we already have to be able to identify the situations when some variable is omitted. When that happens, any value found (on possibly already existing device) should remain unchanged.

Otherwise, for example running the role over pre-existing encrypted volume without encryption option in the task would force default absent value on it and change the device.

[richm]

The way the current role (current contents of main, not this PR) works is this: if fs_type is omitted, or has the value of null, an fs is created with a type of xfs (on RHEL 8.9 manage nodes anyway). I don't think we should change this behavior as it would break the existing API. I have verified this by using the test tests_create_disk_then_remove.yml and using various different values for, or omitting, fs_type.

[vojtechtrefny]

I think a better option to avoid breaking the api is to use a special value for fs_type e.g. fs_type: NOFS which will create the volume with no fs, or remove the fs on an existing volume.

We are currently using unformatted in blivet-gui and empty in udisks so these would be also options. There is a (old and probably never really used) filesystem called NoFS so we should probably avoid using that.

[japokorn]

Using ansible 'false' equivalents might be interchangeable with None, so based on discussion with vtrefny I have changed the string from None to all case variations of unformatted.
I added this to README and also modified the commit message accordingly.

[richm]

or maybe this should be "unconfigured"?

[richm]

Not sure how we note destructive operations elsewhere, but seems to me like we should say something like **WARNING**: Using "unconfigured" on an existing filesystem will remove the filesystem.

[japokorn]

Thanks. The correct value is actually 'unformatted' in the code. I made sure the value is unified.
I have also added a warning note into the README.

[richm]

ok - I also did a test with

        storage_pools:
          - name: foo
            disks: "{{ unused_disks }}"
            volumes:
              - name: test1
                size: "{{ volume_size }}"
                fs_type: unformatted

i.e. create a volume without an FS - it worked fine