Initial support for bind mounts

Separate MountSource from Mount. This is needed to allow
mounts to be shared by multiple containers within the same
pod.

PiperOrigin-RevId: 249617810
Change-Id: Id2944feb7e4194951f355cbe6d4944ae3c02e468

1 files changed, 108 insertions, 59 deletions

diff --git a/pkg/sentry/fs/mount_test.go b/pkg/sentry/fs/mount_test.go
index 9f7fbeff2..2e2716643 100644
--- a/pkg/sentry/fs/mount_test.go
+++ b/pkg/sentry/fs/mount_test.go
@@ -32,6 +32,27 @@ func cacheReallyContains(cache *DirentCache, d *Dirent) bool {
 	return false
 }
 
+func mountPathsAre(root *Dirent, got []*Mount, want ...string) error {
+	gotPaths := make(map[string]struct{}, len(got))
+	gotStr := make([]string, len(got))
+	for i, g := range got {
+		groot := g.Root()
+		name, _ := groot.FullName(root)
+		groot.DecRef()
+		gotStr[i] = name
+		gotPaths[name] = struct{}{}
+	}
+	if len(got) != len(want) {
+		return fmt.Errorf("mount paths are different, got: %q, want: %q", gotStr, want)
+	}
+	for _, w := range want {
+		if _, ok := gotPaths[w]; !ok {
+			return fmt.Errorf("no mount with path %q found", w)
+		}
+	}
+	return nil
+}
+
 // TestMountSourceOnlyCachedOnce tests that a Dirent that is mounted over only ends
 // up in a single Dirent Cache. NOTE(b/63848693): Having a dirent in multiple
 // caches causes major consistency issues.
@@ -91,8 +112,7 @@ func TestMountSourceOnlyCachedOnce(t *testing.T) {
 	}
 }
 
-// Test that mounts have proper parent/child relationships.
-func TestMountSourceParentChildRelationship(t *testing.T) {
+func TestAllMountsUnder(t *testing.T) {
 	ctx := contexttest.Context(t)
 
 	rootCache := NewDirentCache(100)
@@ -122,101 +142,130 @@ func TestMountSourceParentChildRelationship(t *testing.T) {
 		if err != nil {
 			t.Fatalf("could not find path %q in mount manager: %v", p, err)
 		}
+
 		submountInode := NewMockInode(ctx, NewMockMountSource(nil), StableAttr{
 			Type: Directory,
 		})
 		if err := mm.Mount(ctx, d, submountInode); err != nil {
 			t.Fatalf("could not mount at %q: %v", p, err)
 		}
+		d.DecRef()
 	}
 
-	// mm root should contain all submounts (and does not include the root
-	// mount).
-	allMountSources := rootDirent.Inode.MountSource.Submounts()
-	if err := mountPathsAre(rootDirent, allMountSources, paths...); err != nil {
+	// mm root should contain all submounts (and does not include the root mount).
+	rootMnt := mm.FindMount(rootDirent)
+	submounts := mm.AllMountsUnder(rootMnt)
+	allPaths := append(paths, "/")
+	if err := mountPathsAre(rootDirent, submounts, allPaths...); err != nil {
 		t.Error(err)
 	}
 
 	// Each mount should have a unique ID.
 	foundIDs := make(map[uint64]struct{})
-	for _, m := range allMountSources {
-		id := m.ID()
-		if _, ok := foundIDs[id]; ok {
-			t.Errorf("got multiple mounts with id %d", id)
+	for _, m := range submounts {
+		if _, ok := foundIDs[m.ID]; ok {
+			t.Errorf("got multiple mounts with id %d", m.ID)
 		}
-		foundIDs[id] = struct{}{}
+		foundIDs[m.ID] = struct{}{}
 	}
 
 	// Root mount should have no parent.
-	rootMountSource := mm.root.Inode.MountSource
-	if p := rootMountSource.Parent(); p != nil {
+	if p := rootMnt.ParentID; p != invalidMountID {
 		t.Errorf("root.Parent got %v wanted nil", p)
 	}
 
-	// Root mount should have 2 children: foo and waldo.
-	rootChildren := rootMountSource.Children()
-	if err := mountPathsAre(rootDirent, rootChildren, "/foo", "/waldo"); err != nil {
-		t.Error(err)
-	}
-	// All root mount children should have root as parent.
-	for _, c := range rootChildren {
-		if p := c.Parent(); p != rootMountSource {
-			t.Errorf("root mount child got parent %+v, wanted root mount", p)
-		}
-	}
-
-	// "foo" mount should have two children: /foo/bar, and /foo/qux.
+	// Check that "foo" mount has 3 children.
 	maxTraversals = 0
 	d, err := mm.FindLink(ctx, rootDirent, nil, "/foo", &maxTraversals)
 	if err != nil {
 		t.Fatalf("could not find path %q in mount manager: %v", "/foo", err)
 	}
-	fooMountSource := d.Inode.MountSource
-	fooMountSourceChildren := fooMountSource.Children()
-	if err := mountPathsAre(rootDirent, fooMountSourceChildren, "/foo/bar", "/foo/qux"); err != nil {
-		t.Error(err)
-	}
-	// Each child should have fooMountSource as parent.
-	for _, c := range fooMountSourceChildren {
-		if p := c.Parent(); p != fooMountSource {
-			t.Errorf("foo mount child got parent %+v, wanted foo mount", p)
-		}
-	}
-	// Submounts of foo are /foo/bar, /foo/qux, and /foo/bar/baz.
-	if err := mountPathsAre(rootDirent, fooMountSource.Submounts(), "/foo/bar", "/foo/qux", "/foo/bar/baz"); err != nil {
+	defer d.DecRef()
+	submounts = mm.AllMountsUnder(mm.FindMount(d))
+	if err := mountPathsAre(rootDirent, submounts, "/foo", "/foo/bar", "/foo/qux", "/foo/bar/baz"); err != nil {
 		t.Error(err)
 	}
 
-	// "waldo" mount should have no submounts or children.
+	// "waldo" mount should have no children.
 	maxTraversals = 0
 	waldo, err := mm.FindLink(ctx, rootDirent, nil, "/waldo", &maxTraversals)
 	if err != nil {
 		t.Fatalf("could not find path %q in mount manager: %v", "/waldo", err)
 	}
-	waldoMountSource := waldo.Inode.MountSource
-	if got := len(waldoMountSource.Children()); got != 0 {
-		t.Errorf("waldo got %d children, wanted 0", got)
-	}
-	if got := len(waldoMountSource.Submounts()); got != 0 {
-		t.Errorf("waldo got %d children, wanted 0", got)
+	defer waldo.DecRef()
+	submounts = mm.AllMountsUnder(mm.FindMount(waldo))
+	if err := mountPathsAre(rootDirent, submounts, "/waldo"); err != nil {
+		t.Error(err)
 	}
 }
 
-func mountPathsAre(root *Dirent, got []*MountSource, want ...string) error {
-	if len(got) != len(want) {
-		return fmt.Errorf("mount paths have different lengths: got %d want %d", len(got), len(want))
+func TestUnmount(t *testing.T) {
+	ctx := contexttest.Context(t)
+
+	rootCache := NewDirentCache(100)
+	rootInode := NewMockInode(ctx, NewMockMountSource(rootCache), StableAttr{
+		Type: Directory,
+	})
+	mm, err := NewMountNamespace(ctx, rootInode)
+	if err != nil {
+		t.Fatalf("NewMountNamespace failed: %v", err)
 	}
-	gotPaths := make(map[string]struct{}, len(got))
-	for _, g := range got {
-		groot := g.Root()
-		n, _ := groot.FullName(root)
-		groot.DecRef()
-		gotPaths[n] = struct{}{}
+	rootDirent := mm.Root()
+	defer rootDirent.DecRef()
+
+	// Add mounts at the following paths:
+	paths := []string{
+		"/foo",
+		"/foo/bar",
+		"/foo/bar/goo",
+		"/foo/bar/goo/abc",
+		"/foo/abc",
+		"/foo/def",
+		"/waldo",
+		"/wally",
 	}
-	for _, w := range want {
-		if _, ok := gotPaths[w]; !ok {
-			return fmt.Errorf("no mount with path %q found", w)
+
+	var maxTraversals uint
+	for _, p := range paths {
+		maxTraversals = 0
+		d, err := mm.FindLink(ctx, rootDirent, nil, p, &maxTraversals)
+		if err != nil {
+			t.Fatalf("could not find path %q in mount manager: %v", p, err)
+		}
+
+		submountInode := NewMockInode(ctx, NewMockMountSource(nil), StableAttr{
+			Type: Directory,
+		})
+		if err := mm.Mount(ctx, d, submountInode); err != nil {
+			t.Fatalf("could not mount at %q: %v", p, err)
+		}
+		d.DecRef()
+	}
+
+	allPaths := make([]string, len(paths)+1)
+	allPaths[0] = "/"
+	copy(allPaths[1:], paths)
+
+	rootMnt := mm.FindMount(rootDirent)
+	for i := len(paths) - 1; i >= 0; i-- {
+		maxTraversals = 0
+		p := paths[i]
+		d, err := mm.FindLink(ctx, rootDirent, nil, p, &maxTraversals)
+		if err != nil {
+			t.Fatalf("could not find path %q in mount manager: %v", p, err)
+		}
+
+		if err := mm.Unmount(ctx, d, false); err != nil {
+			t.Fatalf("could not unmount at %q: %v", p, err)
+		}
+		d.DecRef()
+
+		// Remove the path that has been unmounted and the check that the remaining
+		// mounts are still there.
+		allPaths = allPaths[:len(allPaths)-1]
+		submounts := mm.AllMountsUnder(rootMnt)
+		if err := mountPathsAre(rootDirent, submounts, allPaths...); err != nil {
+			t.Error(err)
 		}
 	}
-	return nil
 }