devicestate: allow auto-refresh when registration is skipped (noregister)

overlord/devicestate/devicestate.go

@@ -33,6 +33,7 @@ import (
 
 	"github.com/snapcore/snapd/asserts"
 	"github.com/snapcore/snapd/boot"
+	"github.com/snapcore/snapd/dirs"
 	"github.com/snapcore/snapd/gadget"
 	"github.com/snapcore/snapd/i18n"
 	"github.com/snapcore/snapd/logger"
@@ -129,6 +130,15 @@ func canAutoRefresh(st *state.State) (bool, error) {
 		return false, nil
 	}
 
+	// Syncloud runs no serial vault and deliberately skips registration via
+	// the noregister marker, so ensureOperational never attempts registration
+	// and ensureOperationalAttempts stays at 0. Without this the serial check
+	// below would disable auto-refresh forever. Allow it when registration was
+	// intentionally opted out.
+	if osutil.FileExists(filepath.Join(dirs.SnapRunDir, "noregister")) {
+		return true, nil
+	}
+
 	// Either we have a serial or we try anyway if we attempted
 	// for a while to get a serial, this would allow us to at
 	// least upgrade core if that can help.

overlord/devicestate/devicestate_test.go

@@ -1036,6 +1036,37 @@ func (s *deviceMgrSuite) TestCanAutoRefreshNoSerialFallback(c *C) {
 	c.Check(canAutoRefresh(), Equals, true)
 }
 
+func (s *deviceMgrSuite) TestCanAutoRefreshNoRegister(c *C) {
+	s.state.Lock()
+	defer s.state.Unlock()
+
+	canAutoRefresh := func() bool {
+		ok, err := devicestate.CanAutoRefresh(s.state)
+		c.Assert(err, IsNil)
+		return ok
+	}
+
+	// seeded, model, no serial, no registration attempts -> no auto-refresh
+	s.state.Set("seeded", true)
+	devicestatetest.SetDevice(s.state, &auth.DeviceState{
+		Brand: "canonical",
+		Model: "pc",
+	})
+	s.makeModelAssertionInState(c, "canonical", "pc", map[string]interface{}{
+		"architecture": "amd64",
+		"kernel":       "pc-kernel",
+		"gadget":       "pc",
+	})
+	c.Check(devicestate.EnsureOperationalAttempts(s.state), Equals, 0)
+	c.Check(canAutoRefresh(), Equals, false)
+
+	// registration deliberately skipped via the noregister marker
+	// -> auto-refresh without a serial or any registration attempts
+	c.Assert(os.MkdirAll(dirs.SnapRunDir, 0755), IsNil)
+	c.Assert(ioutil.WriteFile(filepath.Join(dirs.SnapRunDir, "noregister"), nil, 0644), IsNil)
+	c.Check(canAutoRefresh(), Equals, true)
+}
+
 func (s *deviceMgrSuite) TestCanAutoRefreshOnClassic(c *C) {
 	release.OnClassic = true