kola: Add soft-reboot support for external tests

Implements soft-reboot capabilities for Kola,
it enables tests to use systemd's soft-reboot functionality.

The implementation follows the same pattern as regular reboots but
for `systemctl soft-reboot`, tracks systemd boot
timestamps rather than kernel boot IDs for state detection.

Co-Authored-By: Colin Walters <[email protected]>
Co-Authored-By: Claude <[email protected]>

Signed-off-by: Colin Walters <[email protected]>
Signed-off-by: Joseph Marrero Corchado <[email protected]>

Author: jmarrero

docs/kola/external-tests.md

@@ -110,6 +110,37 @@ it out.
 (Previously the API for this was to send `SIGTERM` to the current process; that
 method is deprecated and will be removed at some point)
 
+## Support for soft-rebooting
+
+Kola also supports soft-rebooting using systemd's `systemctl soft-reboot` command.
+Soft-reboot restarts the userspace while keeping the kernel and hardware state intact.
+This is useful for testing userspace updates without a full system reboot.
+
+The soft-reboot API is similar to the regular reboot API:
+
+```
+#!/bin/bash
+# Example of soft-reboot test
+set -xeuo pipefail
+case "${AUTOPKGTEST_REBOOT_MARK:-}" in
+  "") echo "test beginning"; /tmp/autopkgtest-soft-reboot mark1 ;;
+  mark1) echo "test in mark1"; /tmp/autopkgtest-soft-reboot mark2 ;;
+  mark2) echo "test in mark2" ;;
+  *) echo "unexpected mark: ${AUTOPKGTEST_REBOOT_MARK}"; exit 1;;
+esac
+echo "ok autopkgtest soft-rebooting"
+```
+
+Key differences with soft-reboot:
+- The kernel boot ID (`/proc/sys/kernel/random/boot_id`) remains the same
+- Hardware state and kernel memory are preserved
+- `/run` is not cycled.
+- Only userspace is restarted
+- Uses `systemctl soft-reboot` instead of `reboot`
+
+Both `/tmp/autopkgtest-soft-reboot` and `/tmp/autopkgtest-soft-reboot-prepare` scripts are available,
+analogous to their regular reboot counterparts.
+
 ## HTTP Server
 
 The `kolet` binary is copied into the `/usr/local/bin/` directory on the CoreOS

mantle/cmd/kola/devshell.go

@@ -239,6 +239,8 @@ func runDevShellSSH(ctx context.Context, builder *platform.QemuBuilder, conf *co
 					_ = inst.Kill()
 				case guestStateInReboot:
 					statusMsg = "QEMU guest initiated reboot"
+				case guestStateInSoftReboot:
+					statusMsg = "QEMU guest initiated soft-reboot"
 				case guestStateOpenSshStopped:
 					statusMsg = "QEMU openssh is not listening"
 				case guestStateSshDisconnected:
@@ -285,6 +287,8 @@ const (
 	guestStateInShutdown
 	// guestStateInReboot indicates that the guest has started a reboot
 	guestStateInReboot
+	// guestStateInSoftReboot indicates that the guest has started a soft-reboot
+	guestStateInSoftReboot
 	// guestStateHalted indicates that the guest has halted or shutdown
 	guestStateHalted
 	// guestStateBooting indicates that the instance is in early boot
@@ -325,6 +329,9 @@ func checkWriteState(msg string, c chan<- guestState) {
 	if strings.Contains(msg, "Starting Reboot...") {
 		c <- guestStateInReboot
 	}
+	if strings.Contains(msg, "Reached target soft-reboot") {
+		c <- guestStateInSoftReboot
+	}
 }
 
 type systemdEventMessage struct {
@@ -428,6 +435,11 @@ func watchJournal(builder *platform.QemuBuilder, conf *conf.Conf, stateChan chan
 			messageID:  "7d4958e842da4a758f6c1cdc7b36dcc5",
 			guestState: guestStateInShutdown,
 		},
+		{
+			unit:       "systemd-soft-reboot.service",
+			messageID:  "7d4958e842da4a758f6c1cdc7b36dcc5",
+			guestState: guestStateInSoftReboot,
+		},
 	}
 
 	r, err := builder.VirtioJournal(conf, "-o json --system")

mantle/cmd/kolet/kolet.go

@@ -105,10 +105,25 @@ reboot
 	autopkgtestRebootPrepareScript = `#!/bin/bash
 set -euo pipefail
 exec /usr/local/bin/kolet reboot-request "$1"
+`
+
+	// Soft-reboot support
+	autopkgTestSoftRebootPath   = "/tmp/autopkgtest-soft-reboot"
+	autopkgtestSoftRebootScript = `#!/bin/bash
+set -xeuo pipefail
+/usr/local/bin/kolet soft-reboot-request "$1"
+systemctl soft-reboot
+`
+	autopkgTestSoftRebootPreparePath = "/tmp/autopkgtest-soft-reboot-prepare"
+
+	autopkgtestSoftRebootPrepareScript = `#!/bin/bash
+set -euo pipefail
+exec /usr/local/bin/kolet soft-reboot-request "$1"
 `
 
 	// File used to communicate between the script and the kolet runner internally
-	rebootRequestFifo = "/run/kolet-reboot"
+	rebootRequestFifo     = "/run/kolet-reboot"
+	softRebootRequestFifo = "/run/kolet-soft-reboot"
 )
 
 var (
@@ -140,6 +155,13 @@ var (
 		SilenceUsage: true,
 	}
 
+	cmdSoftReboot = &cobra.Command{
+		Use:          "soft-reboot-request MARK",
+		Short:        "Request a soft reboot",
+		RunE:         runSoftReboot,
+		SilenceUsage: true,
+	}
+
 	cmdHttpd = &cobra.Command{
 		Use:   "httpd",
 		Short: "Start an HTTP server to serve the contents of the file system",
@@ -260,6 +282,11 @@ func initiateReboot(mark string) error {
 }
 
 func mkfifo(path string) error {
+	// Create a FIFO in an idempotent fashion
+	// as /run survives soft-reboots.
+	if _, err := os.Stat(path); err == nil {
+		return nil
+	}
 	c := exec.Command("mkfifo", path)
 	c.Stderr = os.Stderr
 	err := c.Run()
@@ -269,6 +296,20 @@ func mkfifo(path string) error {
 	return nil
 }
 
+func initiateSoftReboot(mark string) error {
+	systemdjournal.Print(systemdjournal.PriInfo, "Processing soft-reboot request")
+	res := kola.KoletResult{
+		SoftReboot: string(mark),
+	}
+	buf, err := json.Marshal(&res)
+	if err != nil {
+		return errors.Wrapf(err, "serializing KoletResult")
+	}
+	fmt.Println(string(buf))
+	systemdjournal.Print(systemdjournal.PriInfo, "Acknowledged soft-reboot request with mark: %s", buf)
+	return nil
+}
+
 func runExtUnit(cmd *cobra.Command, args []string) error {
 	rebootOff, _ := cmd.Flags().GetBool("deny-reboots")
 	// Write the autopkgtest wrappers
@@ -278,10 +319,18 @@ func runExtUnit(cmd *cobra.Command, args []string) error {
 	if err := os.WriteFile(autopkgTestRebootPreparePath, []byte(autopkgtestRebootPrepareScript), 0755); err != nil {
 		return err
 	}
+	// Write the soft-reboot autopkgtest wrappers
+	if err := os.WriteFile(autopkgTestSoftRebootPath, []byte(autopkgtestSoftRebootScript), 0755); err != nil {
+		return err
+	}
+	if err := os.WriteFile(autopkgTestSoftRebootPreparePath, []byte(autopkgtestSoftRebootPrepareScript), 0755); err != nil {
+		return err
+	}
 
 	// Create the reboot cmdline -> login FIFO for the reboot mark and
 	// proxy it into a channel
 	rebootChan := make(chan string)
+	softRebootChan := make(chan string)
 	errChan := make(chan error)
 
 	// We want to prevent certain tests (like non-exclusive tests) from rebooting
@@ -303,6 +352,25 @@ func runExtUnit(cmd *cobra.Command, args []string) error {
 			}
 			rebootChan <- string(buf)
 		}()
+
+		// Create soft-reboot FIFO and channel
+		err = mkfifo(softRebootRequestFifo)
+		if err != nil {
+			return err
+		}
+		go func() {
+			softRebootReader, err := os.Open(softRebootRequestFifo)
+			if err != nil {
+				errChan <- err
+				return
+			}
+			defer softRebootReader.Close()
+			buf, err := io.ReadAll(softRebootReader)
+			if err != nil {
+				errChan <- err
+			}
+			softRebootChan <- string(buf)
+		}()
 	}
 
 	ctx := context.Background()
@@ -344,6 +412,8 @@ func runExtUnit(cmd *cobra.Command, args []string) error {
 			return err
 		case reboot := <-rebootChan:
 			return initiateReboot(reboot)
+		case softReboot := <-softRebootChan:
+			return initiateSoftReboot(softReboot)
 		case m := <-unitevents:
 			for n := range m {
 				if n == unitname {
@@ -397,6 +467,35 @@ func runReboot(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+// runSoftReboot handles soft-reboot requests similar to runReboot but for systemctl soft-reboot
+func runSoftReboot(cmd *cobra.Command, args []string) error {
+	if _, err := os.Stat(softRebootRequestFifo); os.IsNotExist(err) {
+		return errors.New("Soft-reboots are not supported for this test, softRebootRequestFifo does not exist.")
+	}
+
+	mark := args[0]
+	systemdjournal.Print(systemdjournal.PriInfo, "Requesting soft-reboot with mark: %s", mark)
+	err := mkfifo(kola.KoletRebootAckFifo)
+	if err != nil {
+		return err
+	}
+	err = os.WriteFile(softRebootRequestFifo, []byte(mark), 0644)
+	if err != nil {
+		return err
+	}
+	f, err := os.Open(kola.KoletRebootAckFifo)
+	if err != nil {
+		return err
+	}
+	buf := make([]byte, 1)
+	_, err = f.Read(buf)
+	if err != nil {
+		return err
+	}
+	systemdjournal.Print(systemdjournal.PriInfo, "Soft-reboot request acknowledged")
+	return nil
+}
+
 func runHttpd(cmd *cobra.Command, args []string) error {
 	port, _ := cmd.Flags().GetString("port")
 	path, _ := cmd.Flags().GetString("path")
@@ -413,6 +512,8 @@ func main() {
 	root.AddCommand(cmdRunExtUnit)
 	cmdReboot.Args = cobra.ExactArgs(1)
 	root.AddCommand(cmdReboot)
+	cmdSoftReboot.Args = cobra.ExactArgs(1)
+	root.AddCommand(cmdSoftReboot)
 	cmdHttpd.Flags().StringP("port", "", "80", "port")
 	cmdHttpd.Flags().StringP("path", "", "./", "path to filesystem contents to serve")
 	cmdHttpd.Args = cobra.ExactArgs(0)

mantle/kola/harness.go

@@ -255,7 +255,8 @@ const (
 
 // KoletResult is serialized JSON passed from kolet to the harness
 type KoletResult struct {
-	Reboot string
+	Reboot     string
+	SoftReboot string
 }
 
 const KoletExtTestUnit = "kola-runext"
@@ -1105,6 +1106,10 @@ func runExternalTest(c cluster.TestCluster, mach platform.Machine, testNum int)
 		if err != nil {
 			return errors.Wrapf(err, "getting boot id")
 		}
+		softrebootCount, err := platform.GetMachineSoftRebootCount(mach)
+		if err != nil {
+			return errors.Wrapf(err, "getting soft reboot count")
+		}
 		plog.Debug("Starting kolet run-test-unit")
 		if previousRebootState != "" {
 			// quote around the value for systemd
@@ -1137,27 +1142,47 @@ func runExternalTest(c cluster.TestCluster, mach platform.Machine, testNum int)
 				return errors.Wrapf(err, "parsing kolet json %s", string(stdout))
 			}
 		}
-		// If no  reboot is requested, we're done
-		if koletRes.Reboot == "" {
+		// If no reboot or soft-reboot is requested, we're done
+		if koletRes.Reboot == "" && koletRes.SoftReboot == "" {
 			return nil
 		}
 
-		// A reboot is requested
-		previousRebootState = koletRes.Reboot
-		plog.Debugf("Reboot request with mark='%s'", previousRebootState)
-		// This signals to the subject that we have saved the mark, and the subject
-		// can proceed with rebooting.  We stop sshd to ensure that the wait below
-		// doesn't log in while ssh is shutting down.
-		_, _, err = mach.SSH(fmt.Sprintf("sudo /bin/sh -c 'systemctl stop sshd && echo > %s'", KoletRebootAckFifo))
-		if err != nil {
-			return errors.Wrapf(err, "failed to acknowledge reboot")
+		// Handle regular reboot
+		if koletRes.Reboot != "" {
+			previousRebootState = koletRes.Reboot
+			plog.Debugf("Reboot request with mark='%s'", previousRebootState)
+			// This signals to the subject that we have saved the mark, and the subject
+			// can proceed with rebooting.  We stop sshd to ensure that the wait below
+			// doesn't log in while ssh is shutting down.
+			_, _, err = mach.SSH(fmt.Sprintf("sudo /bin/sh -c 'systemctl stop sshd && echo > %s'", KoletRebootAckFifo))
+			if err != nil {
+				return errors.Wrapf(err, "failed to acknowledge reboot")
+			}
+			plog.Debug("Waiting for reboot")
+			err = mach.WaitForReboot(120*time.Second, bootID)
+			if err != nil {
+				return errors.Wrapf(err, "Waiting for reboot")
+			}
+			plog.Debug("Reboot complete")
 		}
-		plog.Debug("Waiting for reboot")
-		err = mach.WaitForReboot(120*time.Second, bootID)
-		if err != nil {
-			return errors.Wrapf(err, "Waiting for reboot")
+
+		// Handle soft-reboot
+		if koletRes.SoftReboot != "" {
+			previousRebootState = koletRes.SoftReboot
+			plog.Debugf("Soft-reboot request with mark='%s'", previousRebootState)
+			// Use the soft reboot count we collected at the beginning of this loop iteration
+			// Acknowledge the soft-reboot request
+			_, _, err = mach.SSH(fmt.Sprintf("sudo /bin/sh -c 'echo > %s'", KoletRebootAckFifo))
+			if err != nil {
+				return errors.Wrapf(err, "failed to acknowledge soft-reboot")
+			}
+			plog.Debug("Waiting for soft-reboot")
+			err = mach.WaitForSoftReboot(120*time.Second, softrebootCount)
+			if err != nil {
+				return errors.Wrapf(err, "Waiting for soft-reboot")
+			}
+			plog.Debug("Soft-reboot complete")
 		}
-		plog.Debug("Reboot complete")
 	}
 }
 

mantle/platform/machine/aws/machine.go

@@ -80,6 +80,10 @@ func (am *machine) WaitForReboot(timeout time.Duration, oldBootId string) error
 	return platform.WaitForMachineReboot(am, am.journal, timeout, oldBootId)
 }
 
+func (am *machine) WaitForSoftReboot(timeout time.Duration, oldSoftRebootsCount string) error {
+	return platform.WaitForMachineSoftReboot(am, am.journal, timeout, oldSoftRebootsCount)
+}
+
 func (am *machine) Destroy() {
 	origConsole, err := am.cluster.flight.api.GetConsoleOutput(am.ID())
 	if err != nil {

mantle/platform/machine/azure/machine.go

@@ -108,6 +108,15 @@ func (am *machine) WaitForReboot(timeout time.Duration, oldBootId string) error
 	return am.refetchIPs()
 }
 
+func (am *machine) WaitForSoftReboot(timeout time.Duration, oldSoftRebootsCount string) error {
+	err := platform.WaitForMachineSoftReboot(am, am.journal, timeout, oldSoftRebootsCount)
+	if err != nil {
+		return err
+	}
+	// For soft-reboot, IP addresses should not change, but let's refetch to be safe
+	return am.refetchIPs()
+}
+
 func (am *machine) Destroy() {
 	if err := am.saveConsole(); err != nil {
 		// log error, but do not fail to terminate instance

mantle/platform/machine/do/machine.go

@@ -77,6 +77,10 @@ func (dm *machine) WaitForReboot(timeout time.Duration, oldBootId string) error
 	return platform.WaitForMachineReboot(dm, dm.journal, timeout, oldBootId)
 }
 
+func (dm *machine) WaitForSoftReboot(timeout time.Duration, oldSoftRebootsCount string) error {
+	return platform.WaitForMachineSoftReboot(dm, dm.journal, timeout, oldSoftRebootsCount)
+}
+
 func (dm *machine) Destroy() {
 	if err := dm.cluster.flight.api.DeleteDroplet(context.TODO(), dm.droplet.ID); err != nil {
 		plog.Errorf("Error deleting droplet %v: %v", dm.droplet.ID, err)

mantle/platform/machine/esx/machine.go

@@ -78,6 +78,10 @@ func (em *machine) WaitForReboot(timeout time.Duration, oldBootId string) error
 	return platform.WaitForMachineReboot(em, em.journal, timeout, oldBootId)
 }
 
+func (em *machine) WaitForSoftReboot(timeout time.Duration, oldSoftRebootsCount string) error {
+	return platform.WaitForMachineSoftReboot(em, em.journal, timeout, oldSoftRebootsCount)
+}
+
 func (em *machine) Destroy() {
 	if err := em.cluster.flight.api.TerminateDevice(em.ID()); err != nil {
 		plog.Errorf("Error terminating device %v: %v", em.ID(), err)

mantle/platform/machine/gcloud/machine.go

@@ -78,6 +78,10 @@ func (gm *machine) WaitForReboot(timeout time.Duration, oldBootId string) error
 	return platform.WaitForMachineReboot(gm, gm.journal, timeout, oldBootId)
 }
 
+func (gm *machine) WaitForSoftReboot(timeout time.Duration, oldSoftRebootsCount string) error {
+	return platform.WaitForMachineSoftReboot(gm, gm.journal, timeout, oldSoftRebootsCount)
+}
+
 func (gm *machine) Destroy() {
 	if err := gm.saveConsole(); err != nil {
 		plog.Errorf("Error saving console for instance %v: %v", gm.ID(), err)