gcs: Add SCSIDevice type with remove operation

SCSI devices must be unplugged by the guest before removal on the host
side, to ensure smooth operation. Previously a SCSI device was unplugged
when a LCOWMappedVirtualDisk entry was removed. However, we want to
support multiple mounts per disk, which means we need to decouple unplug
from unmount.

This change introduces a new SCSIDevice resource type that has a remove
operation that can be used by the host to trigger an explicit unplug via
SCSI.

This is a breaking change to the bridge protocol:
- With new host/old guest, the host will attempt a SCSIDevice remove
  which will fail due to being unsupported by the guest.
- With old host/new guest, the host will expect the device to be
  unplugged when the disk is removed, which will no longer occur.

Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

internal/guest/prot/protocol.go

@@ -534,6 +534,12 @@ func UnmarshalContainerModifySettings(b []byte) (*ContainerModifySettings, error
 
 	// Fill in the ResourceType-specific fields.
 	switch msr.ResourceType {
+	case guestresource.ResourceTypeSCSIDevice:
+		msd := &guestresource.SCSIDevice{}
+		if err := commonutils.UnmarshalJSONWithHresult(msrRawSettings, msd); err != nil {
+			return &request, errors.Wrap(err, "failed to unmarshal settings as SCSIDevice")
+		}
+		msr.Settings = msd
 	case guestresource.ResourceTypeMappedVirtualDisk:
 		mvd := &guestresource.LCOWMappedVirtualDisk{}
 		if err := commonutils.UnmarshalJSONWithHresult(msrRawSettings, mvd); err != nil {

internal/guest/runtime/hcsv2/uvm.go

@@ -540,6 +540,8 @@ func (h *Host) CreateContainer(ctx context.Context, id string, settings *prot.VM
 
 func (h *Host) modifyHostSettings(ctx context.Context, containerID string, req *guestrequest.ModificationRequest) (err error) {
 	switch req.ResourceType {
+	case guestresource.ResourceTypeSCSIDevice:
+		return modifySCSIDevice(ctx, req.RequestType, req.Settings.(*guestresource.SCSIDevice))
 	case guestresource.ResourceTypeMappedVirtualDisk:
 		mvd := req.Settings.(*guestresource.LCOWMappedVirtualDisk)
 		// find the actual controller number on the bus and update the incoming request.
@@ -937,6 +939,23 @@ func newInvalidRequestTypeError(rt guestrequest.RequestType) error {
 	return errors.Errorf("the RequestType %q is not supported", rt)
 }
 
+func modifySCSIDevice(
+	ctx context.Context,
+	rt guestrequest.RequestType,
+	msd *guestresource.SCSIDevice,
+) error {
+	switch rt {
+	case guestrequest.RequestTypeRemove:
+		cNum, err := scsi.ActualControllerNumber(ctx, msd.Controller)
+		if err != nil {
+			return err
+		}
+		return scsi.UnplugDevice(ctx, cNum, msd.Lun)
+	default:
+		return newInvalidRequestTypeError(rt)
+	}
+}
+
 func modifyMappedVirtualDisk(
 	ctx context.Context,
 	rt guestrequest.RequestType,
@@ -977,7 +996,7 @@ func modifyMappedVirtualDisk(
 				return err
 			}
 		}
-		return scsi.UnplugDevice(ctx, mvd.Controller, mvd.Lun)
+		return nil
 	default:
 		return newInvalidRequestTypeError(rt)
 	}

internal/protocol/guestresource/resources.go

@@ -18,6 +18,9 @@ const (
 	// ResourceTypeMappedDirectory is the modify resource type for mapped
 	// directories
 	ResourceTypeMappedDirectory guestrequest.ResourceType = "MappedDirectory"
+	// ResourceTypeSCSIDevice is the modify resources type for SCSI devices.
+	// Currently it only supports Remove, to cleanly remove a SCSI device.
+	ResourceTypeSCSIDevice guestrequest.ResourceType = "SCSIDevice"
 	// ResourceTypeMappedVirtualDisk is the modify resource type for mapped
 	// virtual disks
 	ResourceTypeMappedVirtualDisk guestrequest.ResourceType = "MappedVirtualDisk"
@@ -64,6 +67,12 @@ type WCOWCombinedLayers struct {
 
 // Defines the schema for hosted settings passed to GCS and/or OpenGCS
 
+// ResourceTypeSCSIDevice represents a SCSI disk that is attached to the system.
+type SCSIDevice struct {
+	Controller uint8 `json:"Controller,omitempty"`
+	Lun        uint8 `json:"Lun,omitempty"`
+}
+
 // LCOWMappedVirtualDisk represents a disk on the host which is mapped into a
 // directory in the guest in the V2 schema.
 type LCOWMappedVirtualDisk struct {