Change vfs.Dirent.Off to NextOff.

"d_off is the distance from the start of the directory to the start of the next
linux_dirent." - getdents(2).

PiperOrigin-RevId: 270349685

pkg/sentry/fsimpl/ext/directory.go

@@ -190,10 +190,10 @@ func (fd *directoryFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallba
 			}
 
 			if !cb.Handle(vfs.Dirent{
-				Name: child.diskDirent.FileName(),
-				Type: fs.ToDirentType(childType),
-				Ino:  uint64(child.diskDirent.Inode()),
-				Off:  fd.off,
+				Name:    child.diskDirent.FileName(),
+				Type:    fs.ToDirentType(childType),
+				Ino:     uint64(child.diskDirent.Inode()),
+				NextOff: fd.off + 1,
 			}) {
 				dir.childList.InsertBefore(child, fd.iter)
 				return nil

pkg/sentry/fsimpl/ext/ext_test.go

@@ -584,7 +584,7 @@ func TestIterDirents(t *testing.T) {
 			// Ignore the inode number and offset of dirents because those are likely to
 			// change as the underlying image changes.
 			cmpIgnoreFields := cmp.FilterPath(func(p cmp.Path) bool {
-				return p.String() == "Ino" || p.String() == "Off"
+				return p.String() == "Ino" || p.String() == "NextOff"
 			}, cmp.Ignore())
 			if diff := cmp.Diff(cb.dirents, test.want, cmpIgnoreFields); diff != "" {
 				t.Errorf("dirents mismatch (-want +got):\n%s", diff)

pkg/sentry/fsimpl/memfs/directory.go

@@ -75,10 +75,10 @@ func (fd *directoryFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallba
 
 	if fd.off == 0 {
 		if !cb.Handle(vfs.Dirent{
-			Name: ".",
-			Type: linux.DT_DIR,
-			Ino:  vfsd.Impl().(*dentry).inode.ino,
-			Off:  0,
+			Name:    ".",
+			Type:    linux.DT_DIR,
+			Ino:     vfsd.Impl().(*dentry).inode.ino,
+			NextOff: 1,
 		}) {
 			return nil
 		}
@@ -87,10 +87,10 @@ func (fd *directoryFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallba
 	if fd.off == 1 {
 		parentInode := vfsd.ParentOrSelf().Impl().(*dentry).inode
 		if !cb.Handle(vfs.Dirent{
-			Name: "..",
-			Type: parentInode.direntType(),
-			Ino:  parentInode.ino,
-			Off:  1,
+			Name:    "..",
+			Type:    parentInode.direntType(),
+			Ino:     parentInode.ino,
+			NextOff: 2,
 		}) {
 			return nil
 		}
@@ -112,10 +112,10 @@ func (fd *directoryFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallba
 		// Skip other directoryFD iterators.
 		if child.inode != nil {
 			if !cb.Handle(vfs.Dirent{
-				Name: child.vfsd.Name(),
-				Type: child.inode.direntType(),
-				Ino:  child.inode.ino,
-				Off:  fd.off,
+				Name:    child.vfsd.Name(),
+				Type:    child.inode.direntType(),
+				Ino:     child.inode.ino,
+				NextOff: fd.off + 1,
 			}) {
 				dir.childList.InsertBefore(child, fd.iter)
 				return nil

pkg/sentry/vfs/file_description.go

@@ -199,8 +199,11 @@ type Dirent struct {
 	// Ino is the inode number.
 	Ino uint64
 
-	// Off is this Dirent's offset.
-	Off int64
+	// NextOff is the offset of the *next* Dirent in the directory; that is,
+	// FileDescription.Seek(NextOff, SEEK_SET) (as called by seekdir(3)) will
+	// cause the next call to FileDescription.IterDirents() to yield the next
+	// Dirent. (The offset of the first Dirent in a directory is always 0.)
+	NextOff int64
 }
 
 // IterDirentsCallback receives Dirents from FileDescriptionImpl.IterDirents.