Assignment sets, implicit device assignment and release

Rather than explicit device assignment, which is carried out by the VM2000 or VM administrator, it is also possible for guest system operators to assign devices to the VM themselves (implicitly), provided the requirements for the VM and the device specified below are met.

Assignment sets

Assignment sets are groups of devices with the ASSIGN-BY-GUEST attribute which, for organizational reasons, are regarded as a unit for implicit device assignment to VMs. VMs can consequently also be separated from each other when devices are assigned implicitly.

Assignment sets are created using /CREATE-VM-ASSIGNMENT-SET and are assigned a unique name (SET-NAME). The assignment set *STDSET is created when VM2000 operation is initialized.

Information on the assignment sets which have been created and the VMs to which they are assigned can be obtained using /SHOW-VM-ASSIGNMENT-SET. The devices which are assigned to an assignment set can be ascertained using /SHOW-VM-DEVICE-STATUS.

Assignment sets are canceled again using /DELETE-VM-ASSIGNMENT-SET. The assignment set *STDSET cannot be deleted.

Requirements of the device for implicit device assignment

Each device which is envisaged for implicit assignment to a VM must have the ASSIGN-BY-GUEST attribute. Devices are assigned the ASSIGN-BY-GUEST attribute using /MODIFY-VM-DEVICE-ATTRIBUTES and in the process are assigned precisely to one created assignment set. This command can also be used to assign the ASSIGN-BY-GUEST attribute and an assignment set to new devices (see "Dynamic I/O configuration modification").

The default value for the ASSIGN-BY-GUEST attribute can be set in the VM2000 parameter file in the monitor system (see "Setting the VM2000 parameters in the parameter service").

Information on whether a device has the ASSIGN-BY-GUEST attribute and the assignment set to which it is assigned can be obtained using /SHOW-VM-DEVICE-STATUS.

The ASSIGN-BY-GUEST attribute can be withdrawn from the device again using /MODIFY-VM-DEVICE-ATTRIBUTES.

Requirements of the VM for implicit device assignment

Each VM which is to be able to implicitly assign itself devices must have the ASSIGN-BY-GUEST privilege for the assignment set to which the required device is assigned. This privilege can be set when the VM is initialized (see "Initializing a VM") or with /MODIFY-VM-ATTRIBUTES; the assignment sets required are then assigned to the VM.

Assignment sets for a VM can be entered in the VM definition with /CREATE- or /MODIFY-VM-DEFINITION. Detailed information can be found in the section "Working with VM definitions".

Information on whether a VM has the ASSIGN-BY-GUEST privilege and the assignment sets which are assigned to it can be obtained using /SHOW-VM-ATTRIBUTES/-RESOURCES INFORMATION=*PRIVILEGES.

/MODIFY-VM-ATTRIBUTES enables to modify the set of assignment sets which is assigned to a VM or to remove the ASSIGN-BY-GUEST privilege from the VM.

Using /SHOW-VM-DEVICE-STATUS SELECT=*PARAMETERS(ASSIGN-BY-GUEST=*YES(SET-NAME=*BY-GUEST(GUEST=<vm-id>))) (/SHOW-VM-DEVICE-STATUS GUEST=<vm-id> for short), the devices can be ascertained which a guest system may assign itself implicitly.

The BS2000 command /SHOW-DEVICE-CONFIGURATION provides information on implicit device assignment options in the guest system (see the “Commands” manual [13] and section "SHOW-DEVICE-CONFIGURATION (Display system configuration and availability)").

A BS2000 console, the home pubset and the paging disks activated at startup must be assigned to the VM explicitly before the guest system is started. Implicit device assignment is not available for devices which should already be attached when the guest system starts up.

Implicit device assignment

The BS2000 command /ATTACH-DEVICE assigns the affected devices to the VM implicitly. At the same time the command attaches the devices in the guest system. The BS2000 commands /UNLOCK-DEVICE and /SHOW-DEVICE-CONFIGURATION UNIT=*PUBSET-DEVICES also use implicit device assignment for the duration of command processing.

Usage mode in the case of implicit device assignment (see section "Usage mode of a device"):

• Disk devices and CRD devices are assigned for shared use (usage mode SHARED).
  Exception: FastDPAV alias devices (SU /390) and emulated disk devices (MU) are assigned for exclusive use.

• Other devices are assigned for exclusive use (usage mode EXCLUSIVE).

• Devices that are already assigned exclusively to another VM cannot be assigned implicitly (exception: MTC devices in the KEEP state, see "Implicit release of devices (state KEEP)").

Implicit release of devices

The BS2000 command /DETACH-DEVICE releases the implicitly assigned devices in the guest system; they are removed from the VM.

The following points are worth noting about the implicit release of devices:

• Devices assigned to a VM implicitly are released at shutdown of the guest system or at /RESET-VM, /DELETE-VM or /START-VM (normal IPL) for the relevant VM.

• In the following cases, implicitly assigned disk devices remain with the VM for diagnostic reasons:

  • abnormal system termination in the guest system

  • system shutdown in the guest system with automatic SLED, e.g. in the case of automatic restart and the restart option DUMP=*SLED

  • /START-VM ...,DIAGNOSTIC-IPL=*YES for the VM

  Exclusive use is changed to shared use. Other, implicitly assigned devices are released.

• For MTC devices that are connected to a tape library system, the implicit device assignment may be preserved after /DETACH-DEVICE. A device like this takes on the status KEEP. Additionally, implicitly assigned MTC devices and emulated disks get the status KEEP temporarily during a VM Migration (SU /390). 

  If /SHOW-VM-DEVICE-STATUS is specified, GUEST(KEEP) appears for this device in the ASSIGNED-BY output column.

  Another VM can assign devices with the status KEEP implicitly. A device with the status KEEP can be released explicitly by means of /REMOVE-VM-DEVICES or /SWITCH-VM-DEVICES ...,FORCE=*NO.

• In the event of an (automatic) restart of the monitor system, the devices assigned implicitly to the monitor VM are released before SYSTEM READY. Message VMS5227 (SU /390) resp. message VMS4009 with Insert BY IPL (SU x86) indicate this for each device that is removed.