qemu/qmp: add new function ExecuteBlockdevAddWithCache

ExecuteBlockdevAddWithCache has two more parameters direct and noFlush
than ExecuteBlockdevAdd.
They are cache-related options for block devices that are described in
https://github.com/qemu/qemu/blob/master/qapi/block-core.json.
direct denotes whether use of O_DIRECT (bypass the host page cache)
is enabled.  noFlush denotes whether flush requests for the device are
ignored.

Signed-off-by: Hui Zhu <teawater@hyper.sh>

qemu/qmp.go

@@ -722,11 +722,7 @@ func (q *QMP) ExecuteQuit(ctx context.Context) error {
 	return q.executeCommand(ctx, "quit", nil, nil)
 }
 
-// ExecuteBlockdevAdd sends a blockdev-add to the QEMU instance.  device is the
-// path of the device to add, e.g., /dev/rdb0, and blockdevID is an identifier
-// used to name the device.  As this identifier will be passed directly to QMP,
-// it must obey QMP's naming rules, e,g., it must start with a letter.
-func (q *QMP) ExecuteBlockdevAdd(ctx context.Context, device, blockdevID string) error {
+func (q *QMP) blockdevAddBaseArgs(device, blockdevID string) (map[string]interface{}, map[string]interface{}) {
 	var args map[string]interface{}
 
 	blockdevArgs := map[string]interface{}{
@@ -747,6 +743,39 @@ func (q *QMP) ExecuteBlockdevAdd(ctx context.Context, device, blockdevID string)
 		}
 	}
 
+	return args, blockdevArgs
+}
+
+// ExecuteBlockdevAdd sends a blockdev-add to the QEMU instance.  device is the
+// path of the device to add, e.g., /dev/rdb0, and blockdevID is an identifier
+// used to name the device.  As this identifier will be passed directly to QMP,
+// it must obey QMP's naming rules, e,g., it must start with a letter.
+func (q *QMP) ExecuteBlockdevAdd(ctx context.Context, device, blockdevID string) error {
+	args, _ := q.blockdevAddBaseArgs(device, blockdevID)
+
+	return q.executeCommand(ctx, "blockdev-add", args, nil)
+}
+
+// ExecuteBlockdevAddWithCache has two more parameters direct and noFlush
+// than ExecuteBlockdevAdd.
+// They are cache-related options for block devices that are described in
+// https://github.com/qemu/qemu/blob/master/qapi/block-core.json.
+// direct denotes whether use of O_DIRECT (bypass the host page cache)
+// is enabled.  noFlush denotes whether flush requests for the device are
+// ignored.
+func (q *QMP) ExecuteBlockdevAddWithCache(ctx context.Context, device, blockdevID string, direct, noFlush bool) error {
+	args, blockdevArgs := q.blockdevAddBaseArgs(device, blockdevID)
+
+	if q.version.Major < 2 || (q.version.Major == 2 && q.version.Minor < 9) {
+		return fmt.Errorf("versions of qemu (%d.%d) older than 2.9 do not support set cache-related options for block devices",
+			q.version.Major, q.version.Minor)
+	}
+
+	blockdevArgs["cache"] = map[string]interface{}{
+		"direct":   direct,
+		"no-flush": noFlush,
+	}
+
 	return q.executeCommand(ctx, "blockdev-add", args, nil)
 }
 

qemu/qmp_test.go

@@ -403,6 +403,30 @@ func TestQMPBlockdevAdd(t *testing.T) {
 	<-disconnectedCh
 }
 
+// Checks that the blockdev-add with cache options command is correctly sent.
+//
+// We start a QMPLoop, send the blockdev-add with cache options
+// command and stop the loop.
+//
+// The blockdev-add with cache options command should be correctly sent and
+// the QMP loop should exit gracefully.
+func TestQMPBlockdevAddWithCache(t *testing.T) {
+	connectedCh := make(chan *QMPVersion)
+	disconnectedCh := make(chan struct{})
+	buf := newQMPTestCommandBuffer(t)
+	buf.AddCommand("blockdev-add", nil, "return", nil)
+	cfg := QMPConfig{Logger: qmpTestLogger{}}
+	q := startQMPLoop(buf, cfg, connectedCh, disconnectedCh)
+	q.version = checkVersion(t, connectedCh)
+	err := q.ExecuteBlockdevAddWithCache(context.Background(), "/dev/rbd0",
+		fmt.Sprintf("drive_%s", volumeUUID), true, true)
+	if err != nil {
+		t.Fatalf("Unexpected error %v", err)
+	}
+	q.Shutdown()
+	<-disconnectedCh
+}
+
 // Checks that the netdev_add command is correctly sent.
 //
 // We start a QMPLoop, send the netdev_add command and stop the loop.