daemon: add ability to use syscall based reboot (#250)

Reboot in the daemon is currently relying on userspace having a shutdown command. This may not always be the case, as Pebble is used in a wide variety of environments.

Add a SetRebootMode() function to the daemon to allow the daemon to be initialised with a syscall based reboot implementation. The default reboot mode using systemd remains unchanged.

internals/daemon/daemon.go

@@ -517,7 +517,7 @@ func (d *Daemon) HandleRestart(t restart.RestartType) {
 	case restart.RestartSystem:
 		// try to schedule a fallback slow reboot already here
 		// in case we get stuck shutting down
-		if err := reboot(rebootWaitTimeout); err != nil {
+		if err := rebootHandler(rebootWaitTimeout); err != nil {
 			logger.Noticef("%s", err)
 		}
 
@@ -693,11 +693,11 @@ func (d *Daemon) doReboot(sigCh chan<- os.Signal, waitTimeout time.Duration) err
 	}
 	// ask for shutdown and wait for it to happen.
 	// if we exit, pebble will be restarted by systemd
-	if err := reboot(rebootDelay); err != nil {
+	if err := rebootHandler(rebootDelay); err != nil {
 		return err
 	}
 	// wait for reboot to happen
-	logger.Noticef("Waiting for system reboot")
+	logger.Noticef("Waiting for system reboot...")
 	if sigCh != nil {
 		signal.Stop(sigCh)
 		if len(sigCh) > 0 {
@@ -710,21 +710,78 @@ func (d *Daemon) doReboot(sigCh chan<- os.Signal, waitTimeout time.Duration) err
 	return fmt.Errorf("expected reboot did not happen")
 }
 
-var shutdownMsg = "reboot scheduled to update the system"
+const rebootMsg = "reboot scheduled to update the system"
 
-func rebootImpl(rebootDelay time.Duration) error {
+var rebootHandler = systemdModeReboot
+
+type RebootMode int
+
+const (
+	// Reboot uses systemd
+	SystemdMode RebootMode = iota + 1
+	// Reboot uses direct kernel syscalls
+	SyscallMode
+)
+
+// SetRebootMode configures how the system issues a reboot. The default
+// reboot handler mode is SystemdMode, which relies on systemd
+// (or similar) provided functionality to reboot.
+func SetRebootMode(mode RebootMode) {
+	switch mode {
+	case SystemdMode:
+		rebootHandler = systemdModeReboot
+	case SyscallMode:
+		rebootHandler = syscallModeReboot
+	default:
+		panic(fmt.Sprintf("unsupported reboot mode %v", mode))
+	}
+}
+
+// systemdModeReboot assumes a userspace shutdown command exists.
+func systemdModeReboot(rebootDelay time.Duration) error {
 	if rebootDelay < 0 {
 		rebootDelay = 0
 	}
 	mins := int64(rebootDelay / time.Minute)
-	cmd := exec.Command("shutdown", "-r", fmt.Sprintf("+%d", mins), shutdownMsg)
+	cmd := exec.Command("shutdown", "-r", fmt.Sprintf("+%d", mins), rebootMsg)
 	if out, err := cmd.CombinedOutput(); err != nil {
 		return osutil.OutputErr(out, err)
 	}
 	return nil
 }
 
-var reboot = rebootImpl
+var (
+	syscallSync   = syscall.Sync
+	syscallReboot = syscall.Reboot
+)
+
+// syscallModeReboot performs a non-blocking delayed reboot using direct Linux
+// kernel syscalls. If the delay is negative or zero, the reboot is issued
+// immediately.
+//
+// Note: Reboot message not currently supported.
+func syscallModeReboot(rebootDelay time.Duration) error {
+	safeReboot := func() {
+		// As per the requirements of the reboot syscall, we
+		// have to first call sync.
+		syscallSync()
+		err := syscallReboot(syscall.LINUX_REBOOT_CMD_RESTART)
+		if err != nil {
+			logger.Noticef("Failed on reboot syscall: %v", err)
+		}
+	}
+
+	if rebootDelay <= 0 {
+		// Synchronous reboot right now.
+		safeReboot()
+	} else {
+		// Asynchronous non-blocking reboot scheduled
+		time.AfterFunc(rebootDelay, func() {
+			safeReboot()
+		})
+	}
+	return nil
+}
 
 func (d *Daemon) Dying() <-chan struct{} {
 	return d.tomb.Dying()

internals/daemon/daemon_test.go

@@ -32,6 +32,7 @@ import (
 	"github.com/gorilla/mux"
 	. "gopkg.in/check.v1"
 
+	"github.com/canonical/pebble/internals/logger"
 	"github.com/canonical/pebble/internals/osutil"
 	"github.com/canonical/pebble/internals/overlord/patch"
 	"github.com/canonical/pebble/internals/overlord/restart"
@@ -693,15 +694,15 @@ func (s *daemonSuite) TestRestartSystemWiring(c *C) {
 	oldRebootNoticeWait := rebootNoticeWait
 	oldRebootWaitTimeout := rebootWaitTimeout
 	defer func() {
-		reboot = rebootImpl
+		rebootHandler = systemdModeReboot
 		rebootNoticeWait = oldRebootNoticeWait
 		rebootWaitTimeout = oldRebootWaitTimeout
 	}()
 	rebootWaitTimeout = 100 * time.Millisecond
 	rebootNoticeWait = 150 * time.Millisecond
 
 	var delays []time.Duration
-	reboot = func(d time.Duration) error {
+	rebootHandler = func(d time.Duration) error {
 		delays = append(delays, d)
 		return nil
 	}
@@ -768,7 +769,7 @@ func (s *daemonSuite) TestRebootHelper(c *C) {
 	}
 
 	for _, t := range tests {
-		err := reboot(t.delay)
+		err := rebootHandler(t.delay)
 		c.Assert(err, IsNil)
 		c.Check(cmd.Calls(), DeepEquals, [][]string{
 			{"shutdown", "-r", t.delayArg, "reboot scheduled to update the system"},
@@ -1176,3 +1177,129 @@ services:
 	c.Assert(tasks, HasLen, 1)
 	c.Check(tasks[0].Kind(), Equals, "stop")
 }
+
+type rebootSuite struct{}
+
+var _ = Suite(&rebootSuite{})
+
+func (s *rebootSuite) TestSyscallPosRebootDelay(c *C) {
+	wait := make(chan struct{})
+	defer FakeSyscallSync(func() {})()
+	defer FakeSyscallReboot(func(cmd int) error {
+		if cmd == syscall.LINUX_REBOOT_CMD_RESTART {
+			close(wait)
+		}
+		return nil
+	})()
+
+	period := 25 * time.Millisecond
+	syscallModeReboot(period)
+	start := time.Now()
+	select {
+	case <-wait:
+	case <-time.After(10 * time.Second):
+		c.Fatal("syscall did not take place and we timed out")
+	}
+	elapsed := time.Now().Sub(start)
+	c.Assert(elapsed >= period, Equals, true)
+}
+
+func (s *rebootSuite) TestSyscallNegRebootDelay(c *C) {
+	wait := make(chan struct{})
+	defer FakeSyscallSync(func() {})()
+	defer FakeSyscallReboot(func(cmd int) error {
+		if cmd == syscall.LINUX_REBOOT_CMD_RESTART {
+			close(wait)
+		}
+		return nil
+	})()
+
+	// Negative periods will be zeroed, so do not fear the huge negative.
+	// We do supply a rather big value here because this test is
+	// effectively a race, but given the huge timeout, it is not going
+	// to be a problem (c).
+	period := 10 * time.Second
+	go func() {
+		// We need a different thread for the unbuffered wait.
+		syscallModeReboot(-period)
+	}()
+	start := time.Now()
+	select {
+	case <-wait:
+	case <-time.After(10 * time.Second):
+		c.Fatal("syscall did not take place and we timed out")
+	}
+	elapsed := time.Now().Sub(start)
+	c.Assert(elapsed < period, Equals, true)
+}
+
+func (s *rebootSuite) TestSetSyscall(c *C) {
+	wait := make(chan struct{})
+	defer FakeSyscallSync(func() {})()
+	defer FakeSyscallReboot(func(cmd int) error {
+		if cmd == syscall.LINUX_REBOOT_CMD_RESTART {
+			close(wait)
+		}
+		return nil
+	})()
+
+	// We know the default is systemdReboot otherwise the unit tests
+	// above will fail. We need to check the switch works.
+	SetRebootMode(SyscallMode)
+	defer SetRebootMode(SystemdMode)
+
+	err := make(chan error)
+	go func() {
+		// We need a different thread for the unbuffered wait.
+		err <- rebootHandler(0)
+	}()
+
+	select {
+	case <-wait:
+	case <-time.After(10 * time.Second):
+		c.Fatal("syscall did not take place and we timed out")
+	}
+	c.Assert(<-err, IsNil)
+}
+
+type fakeLogger struct {
+	msg      string
+	noticeCh chan int
+}
+
+func (f *fakeLogger) Notice(msg string) {
+	f.msg = msg
+	f.noticeCh <- 1
+}
+
+func (f *fakeLogger) Debug(msg string) {}
+
+func (s *rebootSuite) TestSyscallRebootError(c *C) {
+	defer FakeSyscallSync(func() {})()
+	defer FakeSyscallReboot(func(cmd int) error {
+		return fmt.Errorf("-EPERM")
+	})()
+
+	// We know the default is systemdReboot otherwise the unit tests
+	// above will fail. We need to check the switch works.
+	SetRebootMode(SyscallMode)
+	defer SetRebootMode(SystemdMode)
+
+	complete := make(chan int)
+	l := fakeLogger{noticeCh: complete}
+	old := logger.SetLogger(&l)
+	defer logger.SetLogger(old)
+
+	err := make(chan error)
+	go func() {
+		// We need a different thread for the unbuffered wait.
+		err <- rebootHandler(0)
+	}()
+	select {
+	case <-complete:
+	case <-time.After(10 * time.Second):
+		c.Fatal("syscall did not take place and we timed out")
+	}
+	c.Assert(l.msg, Matches, "*-EPERM")
+	c.Assert(<-err, IsNil)
+}

internals/daemon/export_test.go

@@ -46,3 +46,19 @@ func FakeGetChecks(f func(o *overlord.Overlord) ([]*checkstate.CheckInfo, error)
 		getChecks = old
 	}
 }
+
+func FakeSyscallSync(f func()) (restore func()) {
+	old := syscallSync
+	syscallSync = f
+	return func() {
+		syscallSync = old
+	}
+}
+
+func FakeSyscallReboot(f func(cmd int) error) (restore func()) {
+	old := syscallReboot
+	syscallReboot = f
+	return func() {
+		syscallReboot = old
+	}
+}