qmp: add dump-guest-memory support

By adding `dump-guest-memory` command, user can get kernel
memory dump when guest panic occurred.

Fixes: #152

Signed-off-by: bin liu <bin@hyper.sh>

qemu/qmp.go

@@ -268,7 +268,7 @@ func (q *QMP) readLoop(fromVMCh chan<- []byte) {
 	for scanner.Scan() {
 		line := scanner.Bytes()
 		if q.cfg.Logger.V(1) {
-			q.cfg.Logger.Infof("%s", string(line))
+			q.cfg.Logger.Infof("read from QMP: %s", string(line))
 		}
 
 		// Since []byte channel type transfer slice info(include slice underlying array pointer, len, cap)
@@ -1654,3 +1654,14 @@ func (q *QMP) ExecQomGet(ctx context.Context, path, property string) (interface{
 
 	return response, nil
 }
+
+// ExecuteDumpGuestMemory dump guest memory to host
+func (q *QMP) ExecuteDumpGuestMemory(ctx context.Context, protocol string, paging bool, format string) error {
+	args := map[string]interface{}{
+		"protocol": protocol,
+		"paging":   paging,
+		"format":   format,
+	}
+
+	return q.executeCommand(ctx, "dump-guest-memory", args, nil)
+}

qemu/qmp_test.go

@@ -1794,3 +1794,22 @@ func TestExecQomGet(t *testing.T) {
 	q.Shutdown()
 	<-disconnectedCh
 }
+
+// Checks dump-guest-memory
+func TestExecuteDumpGuestMemory(t *testing.T) {
+	connectedCh := make(chan *QMPVersion)
+	disconnectedCh := make(chan struct{})
+	buf := newQMPTestCommandBuffer(t)
+	buf.AddCommand("dump-guest-memory", nil, "return", nil)
+	cfg := QMPConfig{Logger: qmpTestLogger{}}
+	q := startQMPLoop(buf, cfg, connectedCh, disconnectedCh)
+	checkVersion(t, connectedCh)
+
+	err := q.ExecuteDumpGuestMemory(context.Background(), "file:/tmp/dump.xxx.yyy", false, "elf")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	q.Shutdown()
+	<-disconnectedCh
+}