virtcontainers: add method to get hypervisor PID

hypervisor PID can be used to move the whole process and its
threads into a new cgroup.

Signed-off-by: Julio Montes <[email protected]>

virtcontainers/fc.go

@@ -702,3 +702,7 @@ func (fc *firecracker) getThreadIDs() (*threadIDs, error) {
 func (fc *firecracker) cleanup() error {
 	return nil
 }
+
+func (fc *firecracker) pid() int {
+	return fc.info.PID
+}

virtcontainers/hypervisor.go

@@ -609,4 +609,5 @@ type hypervisor interface {
 	hypervisorConfig() HypervisorConfig
 	getThreadIDs() (*threadIDs, error)
 	cleanup() error
+	pid() int
 }

virtcontainers/mock_hypervisor.go

@@ -14,6 +14,7 @@ import (
 )
 
 type mockHypervisor struct {
+	mockPid int
 }
 
 func (m *mockHypervisor) capabilities() types.Capabilities {
@@ -100,3 +101,7 @@ func (m *mockHypervisor) getThreadIDs() (*threadIDs, error) {
 func (m *mockHypervisor) cleanup() error {
 	return nil
 }
+
+func (m *mockHypervisor) pid() int {
+	return m.mockPid
+}

virtcontainers/qemu.go

@@ -8,6 +8,7 @@ package virtcontainers
 import (
 	"context"
 	"fmt"
+	"io/ioutil"
 	"math"
 	"os"
 	"path/filepath"
@@ -500,6 +501,8 @@ func (q *qemu) createSandbox(ctx context.Context, id string, hypervisorConfig *H
 		return err
 	}
 
+	pidFile := q.pidFile()
+
 	qemuConfig := govmmQemu.Config{
 		Name:        fmt.Sprintf("sandbox-%s", q.id),
 		UUID:        q.state.UUID,
@@ -518,6 +521,7 @@ func (q *qemu) createSandbox(ctx context.Context, id string, hypervisorConfig *H
 		VGA:         "none",
 		GlobalParam: "kvm-pit.lost_tick_policy=discard",
 		Bios:        firmwarePath,
+		PidFile:     pidFile,
 	}
 
 	if ioThread != nil {
@@ -1567,3 +1571,23 @@ func (q *qemu) cleanup() error {
 
 	return nil
 }
+
+func (q *qemu) pidFile() string {
+	return filepath.Join(store.RunVMStoragePath, q.id, "pid")
+}
+
+func (q *qemu) pid() int {
+	data, err := ioutil.ReadFile(q.pidFile())
+	if err != nil {
+		q.Logger().WithError(err).Error("Could not read qemu pid file")
+		return 0
+	}
+
+	pid, err := strconv.Atoi(strings.Trim(string(data), "\n\t "))
+	if err != nil {
+		q.Logger().WithError(err).Error("Could not convert string to int")
+		return 0
+	}
+
+	return pid
+}