1 files changed, 75 insertions, 0 deletions
diff --git a/pkg/sentry/vfs/context.go b/pkg/sentry/vfs/context.go
new file mode 100644
index 000000000..c9e724fef
--- /dev/null
+++ b/pkg/sentry/vfs/context.go
@@ -0,0 +1,75 @@
+// 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 vfs
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+)
+
+// contextID is this package's type for context.Context.Value keys.
+type contextID int
+
+const (
+	// CtxMountNamespace is a Context.Value key for a MountNamespace.
+	CtxMountNamespace contextID = iota
+
+	// CtxRoot is a Context.Value key for a VFS root.
+	CtxRoot
+)
+
+// MountNamespaceFromContext returns the MountNamespace used by ctx. If ctx is
+// not associated with a MountNamespace, MountNamespaceFromContext returns nil.
+//
+// A reference is taken on the returned MountNamespace.
+func MountNamespaceFromContext(ctx context.Context) *MountNamespace {
+	if v := ctx.Value(CtxMountNamespace); v != nil {
+		return v.(*MountNamespace)
+	}
+	return nil
+}
+
+// RootFromContext returns the VFS root used by ctx. It takes a reference on
+// the returned VirtualDentry. If ctx does not have a specific VFS root,
+// RootFromContext returns a zero-value VirtualDentry.
+func RootFromContext(ctx context.Context) VirtualDentry {
+	if v := ctx.Value(CtxRoot); v != nil {
+		return v.(VirtualDentry)
+	}
+	return VirtualDentry{}
+}
+
+type rootContext struct {
+	context.Context
+	root VirtualDentry
+}
+
+// WithRoot returns a copy of ctx with the given root.
+func WithRoot(ctx context.Context, root VirtualDentry) context.Context {
+	return &rootContext{
+		Context: ctx,
+		root:    root,
+	}
+}
+
+// Value implements Context.Value.
+func (rc rootContext) Value(key interface{}) interface{} {
+	switch key {
+	case CtxRoot:
+		rc.root.IncRef()
+		return rc.root
+	default:
+		return rc.Context.Value(key)
+	}
+}