pkg/machine/qemu: start VM check if qemu is alive

When trying to connect to the qemu ready socket we should check if the
qemu process is still running, if it is not we can just error out. There
is no point in retrying.
To do so we have to directly call wait with WNOHANG.

Also change StartProcess to os/exec package which is higher level and
allows us to use a buffer as qemu stderr fd.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

pkg/machine/qemu/machine.go

@@ -5,6 +5,7 @@ package qemu
 
 import (
 	"bufio"
+	"bytes"
 	"context"
 	"encoding/base64"
 	"encoding/json"
@@ -138,7 +139,7 @@ func (p *Provider) NewMachine(opts machine.InitOptions) (machine.VM, error) {
 	cmd = append(cmd, []string{
 		"-device", "virtio-serial",
 		// qemu needs to establish the long name; other connections can use the symlink'd
-		// Note both id and chardev start with an extra "a" becuase qemu requires that it
+		// Note both id and chardev start with an extra "a" because qemu requires that it
 		// starts with an letter but users can also use numbers
 		"-chardev", "socket,path=" + vm.ReadySocket.Path + ",server=on,wait=off,id=a" + vm.Name + "_ready",
 		"-device", "virtserialport,chardev=a" + vm.Name + "_ready" + ",name=org.fedoraproject.port.0",
@@ -573,15 +574,25 @@ func (v *MachineVM) Start(name string, _ machine.StartOptions) error {
 	files := []*os.File{dnr, dnw, dnw, fd}
 	attr.Files = files
 	logrus.Debug(v.CmdLine)
-	cmd := v.CmdLine
+	cmdLine := v.CmdLine
 
 	// Disable graphic window when not in debug mode
 	// Done in start, so we're not suck with the debug level we used on init
 	if !logrus.IsLevelEnabled(logrus.DebugLevel) {
-		cmd = append(cmd, "-display", "none")
+		cmdLine = append(cmdLine, "-display", "none")
 	}
 
-	_, err = os.StartProcess(v.CmdLine[0], cmd, attr)
+	stderrBuf := &bytes.Buffer{}
+
+	cmd := &exec.Cmd{
+		Args:       cmdLine,
+		Path:       cmdLine[0],
+		Stdin:      dnr,
+		Stdout:     dnw,
+		Stderr:     stderrBuf,
+		ExtraFiles: []*os.File{fd},
+	}
+	err = cmd.Start()
 	if err != nil {
 		// check if qemu was not found
 		if !errors.Is(err, os.ErrNotExist) {
@@ -592,15 +603,17 @@ func (v *MachineVM) Start(name string, _ machine.StartOptions) error {
 		if err != nil {
 			return err
 		}
-		cmd[0], err = cfg.FindHelperBinary(QemuCommand, true)
+		cmdLine[0], err = cfg.FindHelperBinary(QemuCommand, true)
 		if err != nil {
 			return err
 		}
-		_, err = os.StartProcess(cmd[0], cmd, attr)
+		cmd.Path = cmdLine[0]
+		err = cmd.Start()
 		if err != nil {
 			return fmt.Errorf("unable to execute %q: %w", cmd, err)
 		}
 	}
+	defer cmd.Process.Release() //nolint:errcheck
 	fmt.Println("Waiting for VM ...")
 	socketPath, err := getRuntimeDir()
 	if err != nil {
@@ -615,6 +628,16 @@ func (v *MachineVM) Start(name string, _ machine.StartOptions) error {
 		if err == nil {
 			break
 		}
+		// check if qemu is still alive
+		var status syscall.WaitStatus
+		pid, err := syscall.Wait4(cmd.Process.Pid, &status, syscall.WNOHANG, nil)
+		if err != nil {
+			return fmt.Errorf("failed to read qemu process status: %w", err)
+		}
+		if pid > 0 {
+			// child exited
+			return fmt.Errorf("qemu exited unexpectedly with exit code %d, stderr: %s", status.ExitStatus(), stderrBuf.String())
+		}
 		time.Sleep(wait)
 		wait++
 	}