ext: boilerplate code.

Renamed ext4 to ext since we are targeting ext(2/3/4).
Removed fs.go since we are targeting VFS2.
Added ext.go with filesystem struct.

PiperOrigin-RevId: 257689775

1 files changed, 50 insertions, 0 deletions

diff --git a/pkg/sentry/fs/ext/disklayout/disklayout.go b/pkg/sentry/fs/ext/disklayout/disklayout.go
new file mode 100644
index 000000000..bdf4e2132
--- /dev/null
+++ b/pkg/sentry/fs/ext/disklayout/disklayout.go
@@ -0,0 +1,50 @@
+// 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 provides Linux ext file system's disk level structures
+// which can be directly read into from the underlying device. Structs aim to
+// emulate structures `exactly` how they are layed out on disk.
+//
+// This library aims to be compatible with all ext(2/3/4) systems so it
+// provides a generic interface for all major structures and various
+// implementations (for different versions). The user code is responsible for
+// using appropriate implementations based on the underlying device.
+//
+// Interfacing all major structures here serves a few purposes:
+//   - Abstracts away the complexity of the underlying structure from client
+//     code. The client only has to figure out versioning on set up and then
+//     can use these as black boxes and pass it higher up the stack.
+//   - Having pointer receivers forces the user to use pointers to these
+//     heavy structs. Hence, prevents the client code from unintentionally
+//     copying these by value while passing the interface around.
+//   - Version-based implementation selection is resolved on set up hence
+//     avoiding per call overhead of choosing implementation.
+//   - All interface methods are pretty light weight (do not take in any
+//     parameters by design). Passing pointer arguments to interface methods
+//     can lead to heap allocation as the compiler won't be able to perform
+//     escape analysis on an unknown implementation at compile time.
+//
+// Notes:
+//   - All fields in these structs are exported because binary.Read would
+//     panic otherwise.
+//   - All structures on disk are in little-endian order. Only jbd2 (journal)
+//     structures are in big-endian order.
+//   - All OS dependent fields in these structures will be interpretted using
+//     the Linux version of that field.
+//   - The suffix `Lo` in field names stands for lower bits of that field.
+//   - The suffix `Hi` in field names stands for upper bits of that field.
+//   - The suffix `Raw` has been added to indicate that the field is not split
+//     into Lo and Hi fields and also to resolve name collision with the
+//     respective interface.
+package disklayout