addressed review comments

Author: faisalabujabal

pkg/util/cns.go

@@ -18,6 +18,26 @@ type ControllerID struct {
 	BusNumber      int32
 }
 
+var (
+	// MaxSCSISlotsByType is the maximum number of devices per SCSI controller 
+	// type.
+	// Note: The controller itself occupies one slot.
+	MaxSCSISlotsByType = map[vmopv1.SCSIControllerType]int32{
+		vmopv1.SCSIControllerTypeParaVirtualSCSI: 63, // 64 targets - 1 for controller
+		vmopv1.SCSIControllerTypeBusLogic:        15, // 16 targets - 1 for controller
+		vmopv1.SCSIControllerTypeLsiLogic:        15, // 16 targets - 1 for controller
+		vmopv1.SCSIControllerTypeLsiLogicSAS:     15, // 16 targets - 1 for controller
+	}
+
+	// MaxSCSIControllersPerVM is the maximum number of SCSI controllers 
+	// allowed per VM. (4 controllers, indexed 0-3).
+	MaxSCSIControllersPerVM = int32(4)
+
+	// SCSIControllerUnitNumber is the unit number reserved for SCSI controller 
+	// on its own bus.
+	SCSIControllerUnitNumber = int32(7)
+)
+
 // CNSAttachmentNameForVolume returns the name of the CnsNodeVmAttachment based
 // on the VM and Volume name.
 // This matches the naming used in previous code but there are situations where
@@ -57,3 +77,64 @@ func SanitizeCNSErrorMessage(msg string) string {
 
 	return msg
 }
+
+// MaxSlotsForControllerType returns the maximum number of slots for a
+// controller type.
+// If the controller type is unknown, it defaults to ParaVirtual.
+//
+// PVSCSI supports 64 devices per controller starting
+// vSphere 6.7+. Since min supported vSphere version is >=
+// 8.0, this is a safe assumption.
+//
+// For all these sub-types, the max slots is 1 less than the capacity
+// since SCSI slot 7 is reserved for the controller itself.
+func MaxSlotsForControllerType(ctrlType vmopv1.SCSIControllerType) int32 {
+	if _, ok := MaxSCSISlotsByType[ctrlType]; !ok {
+		// Unknown controller type, default to ParaVirtual
+		return MaxSCSISlotsByType[vmopv1.SCSIControllerTypeParaVirtualSCSI]
+	}
+
+	return MaxSCSISlotsByType[ctrlType]
+}
+
+// ControllerHasAvailableSlots checks if a controller has available slots for
+// new devices.
+func ControllerHasAvailableSlots(
+	controller *vmopv1.SCSIControllerSpec,
+	busNumber int32,
+	statusDeviceCounts, volumeAssignments map[int32]int32,
+) bool {
+	// Get max slots for this controller type
+	maxSlots := MaxSlotsForControllerType(controller.Type)
+
+	// Get current device count from status
+	currentDevices := statusDeviceCounts[busNumber]
+
+	// Get number of volumes already assigned to this controller in this mutation
+	assignedVolumes := volumeAssignments[busNumber]
+
+	// Check if adding one more volume would exceed capacity
+	return (currentDevices + assignedVolumes + 1) <= maxSlots
+}
+
+// FindControllerWithSharing finds a controller with the specified sharing mode
+// and has available slots.
+// Returns the controller if found, nil otherwise.
+func FindControllerWithSharing(
+	sharingMode vmopv1.VirtualControllerSharingMode,
+	controllers map[int32]*vmopv1.SCSIControllerSpec,
+	statusDeviceCounts, volumeAssignments map[int32]int32,
+) *vmopv1.SCSIControllerSpec {
+
+	for busNum := range MaxSCSIControllersPerVM {
+		if controller, exists := controllers[busNum]; exists {
+			if controller.SharingMode == sharingMode &&
+				ControllerHasAvailableSlots(controller, busNum,
+					statusDeviceCounts, volumeAssignments) {
+				return controller
+			}
+		}
+	}
+
+	return nil
+}