Clarify: dedicated disk handling

[johnarwe]

POST /guests allows a list of dedicate_vdevs when creating a guest. The associated request sample omits it, so the format of each entry is ambiguous (string? dict?). DirMaint 7.2's DIRM DEDICATE command documentation suggests that a system device name (rdev or volid) is minimally required for each dedicated device, unless this API carries an implicit assumption that the corresponding directory entry statements would be populated out of band (I find zero other mentions of "dedicated" in the entire REST API doc page).

It's also unclear how any dedicated devices would behave if their vdevs are included on the 3 /guests/{userid}/disks method calls. Presumably (by omission) Feilong does not support adding dedicated disks after the guest is created. Modify and delete might apply regardless of how the disk was created, however.

[johnarwe]

Attach volume and the corresponding Detach API might also figure into this issue. If Attach-volume, for example, adds a DEDICATE statement in the directory entry and/or runs CP ATTACH rdev guest vdev.

[jichenjc]

attach volume is only focus on FCP now, which is DEDICATE XXXX XXXX
while the XXXX is the FCP number ...

[jichenjc]

I don't remember we have dedicate_vdevs for ECKD disk use case, so for ECKD from dasd group
we use MDISK XXX to represent and for persistent storage, DEDICATE XXXX XXXX is used