Created attachment 1168412 [details]
engine log

Description of problem:

Failed to edit a vm's disk from bootable-false to true.
Tried to edit vm's disk with both api versions:

Version 3 - 
url:
https://{engine_url}/ovirt-engine/api/vms/{vm_id}/disks/{disk_id}

PUT body:
<disk>
<bootable>true</bootable>
</disk>

Version 4 - 

PUT body:
<disk_attachment>
<bootable>true</bootable>
</disk_attachment>

In both cases I get 400 rc with the error:
[Interface is required]

Did not find any further information on engine.log

Version-Release number of selected component (if applicable):
rhevm-4.0.0.2-0.1.el7ev.noarch

How reproducible:
so far re produced on 2 different envs

Steps to Reproduce:
1. Create a vm with a disk which is not bootable.
2. Wait until disk is up.
3. Try to edit the disk enable bootable option via API as described above

Actual results:
[Interface is required]

Expected results:
Action succeeds, disk is set to booatable.

Additional info:
2016-06-15 17:35:39,687 WARN  [org.ovirt.engine.core.bll.storage.disk.UpdateVmDiskCommand] (default task-8) [disks_update_d85d3afa-1402-4d92] Validation of action 'UpdateVmDisk' failed for user admin@internal-authz. Reasons: VAR__ACTION__
UPDATE,VAR__TYPE__DISK,VALIDATION_DISK_INTERFACE_NOT_NULL
2016-06-15 17:35:39,688 ERROR [org.ovirt.engine.api.restapi.resource.AbstractBackendResource] (default task-8) [] Operation Failed: [Interface is required]