Implement memmap.MappingIdentity for vfs.FileDescription.

PiperOrigin-RevId: 285255855

1 files changed, 13 insertions, 0 deletions

diff --git a/pkg/sentry/vfs/context.go b/pkg/sentry/vfs/context.go
index 32cf9151b..705194ebc 100644
--- a/pkg/sentry/vfs/context.go
+++ b/pkg/sentry/vfs/context.go
@@ -24,6 +24,9 @@ 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. It does
@@ -35,3 +38,13 @@ func MountNamespaceFromContext(ctx context.Context) *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{}
+}