overlord/fdestate/fdestate.go: fix path to data mount point on hybrid

We used a path that is not a mount point on hybrid to discover the
data disk. Instead we now use / for hybrid, and /writable on core.

overlord/fdestate/fdemgr_test.go

@@ -24,6 +24,7 @@ import (
 	"crypto"
 	"fmt"
 	"os"
+	"path/filepath"
 	"testing"
 
 	. "gopkg.in/check.v1"
@@ -36,6 +37,7 @@ import (
 	"github.com/snapcore/snapd/overlord/fdestate"
 	"github.com/snapcore/snapd/overlord/fdestate/backend"
 	"github.com/snapcore/snapd/overlord/state"
+	"github.com/snapcore/snapd/release"
 	"github.com/snapcore/snapd/secboot"
 	"github.com/snapcore/snapd/snapdenv"
 	"github.com/snapcore/snapd/testutil"
@@ -82,6 +84,8 @@ func (s *fdeMgrSuite) SetUpTest(c *C) {
 	}
 	err := m.WriteTo(dirs.GlobalRootDir)
 	c.Assert(err, IsNil)
+
+	s.AddCleanup(release.MockOnClassic(true))
 }
 
 type instrumentedUnlocker struct {
@@ -101,10 +105,14 @@ func (u *instrumentedUnlocker) Relock() {
 	u.relocked += 1
 }
 
-func (s *fdeMgrSuite) startedManager(c *C) *fdestate.FDEManager {
+func (s *fdeMgrSuite) startedManager(c *C, onClassic bool) *fdestate.FDEManager {
 	defer fdestate.MockDMCryptUUIDFromMountPoint(func(mountpoint string) (string, error) {
 		switch mountpoint {
-		case dirs.SnapdStateDir(dirs.GlobalRootDir):
+		case dirs.GlobalRootDir:
+			c.Check(onClassic, Equals, true)
+			return "aaa", nil
+		case filepath.Join(dirs.GlobalRootDir, "writable"):
+			c.Check(onClassic, Equals, false)
 			return "aaa", nil
 		case dirs.SnapSaveDir:
 			return "bbb", nil
@@ -132,9 +140,10 @@ func (s *fdeMgrSuite) startedManager(c *C) *fdestate.FDEManager {
 	return manager
 }
 
-func (s *fdeMgrSuite) TestGetManagerFromState(c *C) {
+func (s *fdeMgrSuite) testGetManagerFromState(c *C, onClassic bool) {
 	st := s.st
-	manager := s.startedManager(c)
+	s.AddCleanup(release.MockOnClassic(onClassic))
+	manager := s.startedManager(c, onClassic)
 
 	st.Lock()
 	defer st.Unlock()
@@ -151,6 +160,16 @@ func (s *fdeMgrSuite) TestGetManagerFromState(c *C) {
 	c.Check(primaryKey.Digest.Digest, DeepEquals, []byte{5, 6, 7, 8})
 }
 
+func (s *fdeMgrSuite) TestGetManagerFromStateClassic(c *C) {
+	const onClassic = true
+	s.testGetManagerFromState(c, onClassic)
+}
+
+func (s *fdeMgrSuite) TestGetManagerFromStateCore(c *C) {
+	const onClassic = false
+	s.testGetManagerFromState(c, onClassic)
+}
+
 type mockModel struct {
 }
 
@@ -180,7 +199,9 @@ func (m *mockModel) SignKeyID() string {
 
 func (s *fdeMgrSuite) TestUpdateState(c *C) {
 	st := s.st
-	manager := s.startedManager(c)
+	const onClassic = true
+	s.AddCleanup(release.MockOnClassic(onClassic))
+	manager := s.startedManager(c, onClassic)
 
 	st.Lock()
 	defer st.Unlock()
@@ -209,7 +230,9 @@ func (s *fdeMgrSuite) TestUpdateState(c *C) {
 
 func (s *fdeMgrSuite) TestUpdateReseal(c *C) {
 	st := s.st
-	manager := s.startedManager(c)
+	const onClassic = true
+	s.AddCleanup(release.MockOnClassic(onClassic))
+	manager := s.startedManager(c, onClassic)
 
 	st.Lock()
 	defer st.Unlock()
@@ -261,7 +284,7 @@ type mountResolveTestCase struct {
 func (s *fdeMgrSuite) testMountResolveError(c *C, tc mountResolveTestCase) {
 	defer fdestate.MockDMCryptUUIDFromMountPoint(func(mountpoint string) (string, error) {
 		switch mountpoint {
-		case dirs.SnapdStateDir(dirs.GlobalRootDir):
+		case dirs.GlobalRootDir:
 			// ubuntu-data
 			if tc.dataResolveErr != nil {
 				return "", tc.dataResolveErr

overlord/fdestate/fdestate.go

@@ -22,6 +22,7 @@ import (
 	"crypto"
 	"errors"
 	"fmt"
+	"path/filepath"
 
 	"github.com/snapcore/snapd/asserts"
 	"github.com/snapcore/snapd/dirs"
@@ -30,6 +31,7 @@ import (
 	"github.com/snapcore/snapd/osutil"
 	"github.com/snapcore/snapd/osutil/disks"
 	"github.com/snapcore/snapd/overlord/state"
+	"github.com/snapcore/snapd/release"
 	"github.com/snapcore/snapd/secboot"
 )
 
@@ -218,7 +220,14 @@ func initializeState(st *state.State) error {
 
 	// FIXME mount points will be different in recovery or factory-reset modes
 	// either inspect degraded.json, or use boot.HostUbuntuDataForMode()
-	dataUUID, dataErr := disksDMCryptUUIDFromMountPoint(dirs.SnapdStateDir(dirs.GlobalRootDir))
+
+	// On Classic, the data disk is mounted as /
+	dataDir := dirs.GlobalRootDir
+	if !release.OnClassic {
+		// If on Core /writable is a bind mount from data dir
+		dataDir = filepath.Join(dirs.GlobalRootDir, "writable")
+	}
+	dataUUID, dataErr := disksDMCryptUUIDFromMountPoint(dataDir)
 	saveUUID, saveErr := disksDMCryptUUIDFromMountPoint(dirs.SnapSaveDir)
 	if errors.Is(saveErr, disks.ErrMountPointNotFound) {
 		// TODO: do we need to care about old cases where there is no save partition?

overlord/managers_test.go

@@ -7461,7 +7461,9 @@ func (s *mgrsSuiteCore) testRemodelUC20WithRecoverySystem(c *C, encrypted bool)
 
 	restore = fdestate.MockDMCryptUUIDFromMountPoint(func(mountpoint string) (string, error) {
 		switch mountpoint {
-		case dirs.SnapdStateDir(dirs.GlobalRootDir):
+		case filepath.Join(dirs.GlobalRootDir, "writable"):
+			return "root-uuid", nil
+		case dirs.GlobalRootDir:
 			return "root-uuid", nil
 		case dirs.SnapSaveDir:
 			return "save-uuid", nil