Use kernfs.Dentry for kernfs.Lookup.

Updates #1193.

PiperOrigin-RevId: 332939026

3 files changed, 8 insertions, 13 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 89ed265dc..03bcfb1e2 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -127,20 +127,15 @@ func (fs *Filesystem) revalidateChildLocked(ctx context.Context, vfsObj *vfs.Vir
 		}
 	}
 	if child == nil {
-		// Dentry isn't cached; it either doesn't exist or failed
-		// revalidation. Attempt to resolve it via Lookup.
-		//
-		// FIXME(gvisor.dev/issue/1193): Inode.Lookup() should return
-		// *(kernfs.)Dentry, not *vfs.Dentry, since (kernfs.)Filesystem assumes
-		// that all dentries in the filesystem are (kernfs.)Dentry and performs
-		// vfs.DentryImpl casts accordingly.
-		childVFSD, err := parent.inode.Lookup(ctx, name)
+		// Dentry isn't cached; it either doesn't exist or failed revalidation.
+		// Attempt to resolve it via Lookup.
+		c, err := parent.inode.Lookup(ctx, name)
 		if err != nil {
 			return nil, err
 		}
 		// Reference on childVFSD dropped by a corresponding Valid.
-		child = childVFSD.Impl().(*Dentry)
-		parent.InsertChildLocked(name, child)
+		parent.InsertChildLocked(name, c)
+		child = c
 	}
 	return child, nil
 }
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 6ee353ace..1ea4f1c7b 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -130,7 +130,7 @@ func (InodeNotDirectory) Rename(context.Context, string, string, *vfs.Dentry, *v
 }
 
 // Lookup implements Inode.Lookup.
-func (InodeNotDirectory) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+func (InodeNotDirectory) Lookup(ctx context.Context, name string) (*Dentry, error) {
 	panic("Lookup called on non-directory inode")
 }
 
@@ -152,7 +152,7 @@ func (InodeNotDirectory) Valid(context.Context) bool {
 type InodeNoDynamicLookup struct{}
 
 // Lookup implements Inode.Lookup.
-func (InodeNoDynamicLookup) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+func (InodeNoDynamicLookup) Lookup(ctx context.Context, name string) (*Dentry, error) {
 	return nil, syserror.ENOENT
 }
 
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 163f26ceb..7a63e1410 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -449,7 +449,7 @@ type inodeDynamicLookup interface {
 	//
 	// Lookup returns the child with an extra reference and the caller owns this
 	// reference.
-	Lookup(ctx context.Context, name string) (*vfs.Dentry, error)
+	Lookup(ctx context.Context, name string) (*Dentry, error)
 
 	// Valid should return true if this inode is still valid, or needs to
 	// be resolved again by a call to Lookup.