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

2 files changed, 7 insertions, 1 deletions

diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 138adb9f7..5cfb0dc4c 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -400,6 +400,7 @@ func (fs *filesystem) unlinkAt(ctx context.Context, rp *vfs.ResolvingPath, dir b
 	}
 	vfsObj := rp.VirtualFilesystem()
 	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
 	parent.dirMu.Lock()
 	defer parent.dirMu.Unlock()
 	childVFSD := parent.vfsd.Child(name)
@@ -934,7 +935,9 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 	if oldParent == newParent && oldName == newName {
 		return nil
 	}
-	if err := vfsObj.PrepareRenameDentry(vfs.MountNamespaceFromContext(ctx), &renamed.vfsd, replacedVFSD); err != nil {
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	if err := vfsObj.PrepareRenameDentry(mntns, &renamed.vfsd, replacedVFSD); err != nil {
 		return err
 	}
 	if err := renamed.file.rename(ctx, newParent.file, newName); err != nil {
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index d0552bd99..d00850e25 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -52,6 +52,9 @@ import (
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
+// Name is the default filesystem name.
+const Name = "9p"
+
 // FilesystemType implements vfs.FilesystemType.
 type FilesystemType struct{}