Annotation for preferred rootfs type

Signed-off-by: John Howard <jhoward@microsoft.com>

cmd/runhcs/container.go

@@ -241,6 +241,26 @@ func parseAnnotationsBool(a map[string]string, key string) *bool {
 	return nil
 }
 
+// parseAnnotationsPreferredRootFSType searches `a` for `key` and verifies that the
+// value is in the set of allowed values. If `key` is not found returns `nil`.
+// Otherwise returns the index at which it was found in allowed values.
+func parseAnnotationsPreferredRootFSType(a map[string]string, key string) *uvm.PreferredRootFSType {
+	if v, ok := a[key]; ok {
+		// Following array must match enumeration uvm.PreferredRootFSType indexes
+		possibles := []string{"initrd", "vhd"}
+		for index, possible := range possibles {
+			if possible == v {
+				prfstype := uvm.PreferredRootFSType(index)
+				return &prfstype
+			}
+		}
+		logrus.Warningf("annotation: '%s', with value: '%s' must be one of %q", key, v, possibles)
+		return nil
+
+	}
+	return nil
+}
+
 // parseAnnotationsUint32 searches `a` for `key` and if found verifies that the
 // value is a 32 bit unsigned integer. If `key` is not found returns `nil`.
 func parseAnnotationsUint32(a map[string]string, key string) *uint32 {
@@ -449,6 +469,7 @@ func createContainer(cfg *containerConfig) (_ *container, err error) {
 			annotationEnableDeferredCommit = "io.microsoft.virtualmachine.computetopology.memory.enabledeferredcommit"
 			annotationVPMemCount           = "io.microsoft.virtualmachine.devices.virtualpmem.maximumcount"
 			annotationVPMemSize            = "io.microsoft.virtualmachine.devices.virtualpmem.maximumsizebytes"
+			annotationPreferredRootFSType  = "io.microsoft.virtualmachine.lcow.preferredrootfstype"
 		)
 
 		opts := &uvm.UVMOptions{
@@ -461,6 +482,7 @@ func createContainer(cfg *containerConfig) (_ *container, err error) {
 			EnableDeferredCommit: parseAnnotationsBool(cfg.Spec.Annotations, annotationEnableDeferredCommit),
 			VPMemDeviceCount:     parseAnnotationsUint32(cfg.Spec.Annotations, annotationVPMemCount),
 			VPMemSizeBytes:       parseAnnotationsUint64(cfg.Spec.Annotations, annotationVPMemSize),
+			PreferredRootFSType:  parseAnnotationsPreferredRootFSType(cfg.Spec.Annotations, annotationPreferredRootFSType),
 		}
 
 		shim, err := c.startVMShim(cfg.VMLogFile, opts)

internal/uvm/create.go

@@ -44,20 +44,31 @@ type UVMOptions struct {
 	LayerFolders []string // Set of folders for base layers and scratch. Ordered from top most read-only through base read-only layer, followed by scratch
 
 	// LCOW specific parameters
-	BootFilesPath         string               // Folder in which kernel and root file system reside. Defaults to \Program Files\Linux Containers
-	KernelFile            string               // Filename under BootFilesPath for the kernel. Defaults to `kernel`
-	RootFSFile            string               // Filename under BootFilesPath for the UVMs root file system. Defaults are `initrd.img` or `rootfs.vhd`.
-	PreferredRootFSType   *PreferredRootFSType // Controls searching for the RootFSFile.
-	KernelBootOptions     string               // Additional boot options for the kernel
-	EnableGraphicsConsole bool                 // If true, enable a graphics console for the utility VM
-	ConsolePipe           string               // The named pipe path to use for the serial console.  eg \\.\pipe\vmpipe
-	SCSIControllerCount   *int                 // The number of SCSI controllers. Defaults to 1 if omitted. Currently we only support 0 or 1.
+	BootFilesPath         string // Folder in which kernel and root file system reside. Defaults to \Program Files\Linux Containers
+	KernelFile            string // Filename under BootFilesPath for the kernel. Defaults to `kernel`
+	RootFSFile            string // Filename under BootFilesPath for the UVMs root file system. Defaults are `initrd.img` or `rootfs.vhd`.
+	KernelBootOptions     string // Additional boot options for the kernel
+	EnableGraphicsConsole bool   // If true, enable a graphics console for the utility VM
+	ConsolePipe           string // The named pipe path to use for the serial console.  eg \\.\pipe\vmpipe
+	SCSIControllerCount   *int   // The number of SCSI controllers. Defaults to 1 if omitted. Currently we only support 0 or 1.
 
 	// Fields that can be configured via OCI annotations in runhcs.
-	AllowOvercommit      *bool   // Memory for UVM. Defaults to true. For physical backed memory, set to false. io.microsoft.virtualmachine.computetopology.memory.allowovercommit=true|false
-	EnableDeferredCommit *bool   // Memory for UVM. Defaults to false. For virtual memory with deferred commit, set to true. io.microsoft.virtualmachine.computetopology.memory.enabledeferredcommit=true|false
-	VPMemDeviceCount     *uint32 // Number of VPMem devices. Limit at 128. If booting UVM from VHD, device 0 is taken. LCOW Only. io.microsoft.virtualmachine.devices.virtualpmem.maximumcount
-	VPMemSizeBytes       *uint64 // Size of the VPMem devices. LCOW Only. Defaults to 4GB. io.microsoft.virtualmachine.devices.virtualpmem.maximumsizebytes
+
+	// Memory for UVM. Defaults to true. For physical backed memory, set to false. io.microsoft.virtualmachine.computetopology.memory.allowovercommit=true|false
+	AllowOvercommit *bool
+
+	// Memory for UVM. Defaults to false. For virtual memory with deferred commit, set to true. io.microsoft.virtualmachine.computetopology.memory.enabledeferredcommit=true|false
+	EnableDeferredCommit *bool
+
+	// Number of VPMem devices. Limit at 128. If booting UVM from VHD, device 0 is taken. LCOW Only. io.microsoft.virtualmachine.devices.virtualpmem.maximumcount
+	VPMemDeviceCount *uint32
+
+	// Size of the VPMem devices. LCOW Only. Defaults to 4GB. io.microsoft.virtualmachine.devices.virtualpmem.maximumsizebytes
+	VPMemSizeBytes *uint64
+
+	// Controls searching for the RootFSFile. Defaults to initrd (0). Can be set to VHD (1). io.microsoft.virtualmachine.lcow.preferredrootfstype
+	// Note this uses an arbitrary annotation strict which has no direct mapping to the HCS schema.
+	PreferredRootFSType *PreferredRootFSType
 }
 
 const linuxLogVsockPort = 109
@@ -101,7 +112,7 @@ func Create(opts *UVMOptions) (_ *UtilityVM, err error) {
 	attachments := make(map[string]hcsschema.Attachment)
 	scsi := make(map[string]hcsschema.Scsi)
 	uvm.scsiControllerCount = 1
-	var actualRootFSType PreferredRootFSType = PreferredRootFSTypeInitRd // TODO Should we switch to VPMem/VHD as default?
+	var actualRootFSType PreferredRootFSType = PreferredRootFSTypeInitRd
 
 	if uvm.operatingSystem == "windows" {
 		if len(opts.LayerFolders) < 2 {