1 files changed, 72 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/ext/disklayout/dirent.go b/pkg/sentry/fsimpl/ext/disklayout/dirent.go
new file mode 100644
index 000000000..417b6cf65
--- /dev/null
+++ b/pkg/sentry/fsimpl/ext/disklayout/dirent.go
@@ -0,0 +1,72 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package disklayout
+
+import (
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+)
+
+const (
+	// MaxFileName is the maximum length of an ext fs file's name.
+	MaxFileName = 255
+
+	// DirentSize is the size of ext dirent structures.
+	DirentSize = 263
+)
+
+var (
+	// inodeTypeByFileType maps ext4 file types to vfs inode types.
+	//
+	// See https://www.kernel.org/doc/html/latest/filesystems/ext4/dynamic.html#ftype.
+	inodeTypeByFileType = map[uint8]fs.InodeType{
+		0: fs.Anonymous,
+		1: fs.RegularFile,
+		2: fs.Directory,
+		3: fs.CharacterDevice,
+		4: fs.BlockDevice,
+		5: fs.Pipe,
+		6: fs.Socket,
+		7: fs.Symlink,
+	}
+)
+
+// The Dirent interface should be implemented by structs representing ext
+// directory entries. These are for the linear classical directories which
+// just store a list of dirent structs. A directory is a series of data blocks
+// where is each data block contains a linear array of dirents. The last entry
+// of the block has a record size that takes it to the end of the block. The
+// end of the directory is when you read dirInode.Size() bytes from the blocks.
+//
+// See https://www.kernel.org/doc/html/latest/filesystems/ext4/dynamic.html#linear-classic-directories.
+type Dirent interface {
+	// Inode returns the absolute inode number of the underlying inode.
+	// Inode number 0 signifies an unused dirent.
+	Inode() uint32
+
+	// RecordSize returns the record length of this dirent on disk. The next
+	// dirent in the dirent list should be read after these many bytes from
+	// the current dirent. Must be a multiple of 4.
+	RecordSize() uint16
+
+	// FileName returns the name of the file. Can be at most 255 is length.
+	FileName() string
+
+	// FileType returns the inode type of the underlying inode. This is a
+	// performance hack so that we do not have to read the underlying inode struct
+	// to know the type of inode. This will only work when the SbDirentFileType
+	// feature is set. If not, the second returned value will be false indicating
+	// that user code has to use the inode mode to extract the file type.
+	FileType() (fs.InodeType, bool)
+}