Plumb VFS2 inside the Sentry

- Added fsbridge package with interface that can be used to open
  and read from VFS1 and VFS2 files.
- Converted ELF loader to use fsbridge
- Added VFS2 types to FSContext
- Added vfs.MountNamespace to ThreadGroup

Updates #1623

PiperOrigin-RevId: 295183950

1 files changed, 54 insertions, 0 deletions

diff --git a/pkg/sentry/fsbridge/bridge.go b/pkg/sentry/fsbridge/bridge.go
new file mode 100644
index 000000000..8e7590721
--- /dev/null
+++ b/pkg/sentry/fsbridge/bridge.go
@@ -0,0 +1,54 @@
+// Copyright 2020 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 fsbridge provides common interfaces to bridge between VFS1 and VFS2
+// files.
+package fsbridge
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// File provides a common interface to bridge between VFS1 and VFS2 files.
+type File interface {
+	// PathnameWithDeleted returns an absolute pathname to vd, consistent with
+	// Linux's d_path(). In particular, if vd.Dentry() has been disowned,
+	// PathnameWithDeleted appends " (deleted)" to the returned pathname.
+	PathnameWithDeleted(ctx context.Context) string
+
+	// ReadFull read all contents from the file.
+	ReadFull(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error)
+
+	// ConfigureMMap mutates opts to implement mmap(2) for the file.
+	ConfigureMMap(context.Context, *memmap.MMapOpts) error
+
+	// Type returns the file type, e.g. linux.S_IFREG.
+	Type(context.Context) (linux.FileMode, error)
+
+	// IncRef increments reference.
+	IncRef()
+
+	// DecRef decrements reference.
+	DecRef()
+}
+
+// Lookup provides a common interface to open files.
+type Lookup interface {
+	// OpenPath opens a file.
+	OpenPath(ctx context.Context, path string, opts vfs.OpenOptions, remainingTraversals *uint, resolveFinal bool) (File, error)
+}