Add FilesystemType.Name method, and FilesystemType field to Filesystem struct.

Both have analogues in Linux:
* struct file_system_type has a char *name field.
* struct super_block keeps a pointer to the file_system_type.

These fields are necessary to support the `filesystem type` field in
/proc/[pid]/mountinfo.

PiperOrigin-RevId: 303434063

4 files changed, 27 insertions, 2 deletions

diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
index f58867066..d1f6dfb45 100644
--- a/pkg/sentry/vfs/anonfs.go
+++ b/pkg/sentry/vfs/anonfs.go
@@ -51,6 +51,19 @@ const (
 	anonFileGID  = auth.RootKGID
 )
 
+// anonFilesystemType implements FilesystemType.
+type anonFilesystemType struct{}
+
+// GetFilesystem implements FilesystemType.GetFilesystem.
+func (anonFilesystemType) GetFilesystem(context.Context, *VirtualFilesystem, *auth.Credentials, string, GetFilesystemOptions) (*Filesystem, *Dentry, error) {
+	panic("cannot instaniate an anon filesystem")
+}
+
+// Name implemenents FilesystemType.Name.
+func (anonFilesystemType) Name() string {
+	return "none"
+}
+
 // anonFilesystem is the implementation of FilesystemImpl that backs
 // VirtualDentries returned by VirtualFilesystem.NewAnonVirtualDentry().
 //
diff --git a/pkg/sentry/vfs/filesystem.go b/pkg/sentry/vfs/filesystem.go
index 7b7d233f9..cd34782ff 100644
--- a/pkg/sentry/vfs/filesystem.go
+++ b/pkg/sentry/vfs/filesystem.go
@@ -42,21 +42,30 @@ type Filesystem struct {
 	// immutable.
 	vfs *VirtualFilesystem
 
+	// fsType is the FilesystemType of this Filesystem.
+	fsType FilesystemType
+
 	// impl is the FilesystemImpl associated with this Filesystem. impl is
 	// immutable. This should be the last field in Dentry.
 	impl FilesystemImpl
 }
 
 // Init must be called before first use of fs.
-func (fs *Filesystem) Init(vfsObj *VirtualFilesystem, impl FilesystemImpl) {
+func (fs *Filesystem) Init(vfsObj *VirtualFilesystem, fsType FilesystemType, impl FilesystemImpl) {
 	fs.refs = 1
 	fs.vfs = vfsObj
+	fs.fsType = fsType
 	fs.impl = impl
 	vfsObj.filesystemsMu.Lock()
 	vfsObj.filesystems[fs] = struct{}{}
 	vfsObj.filesystemsMu.Unlock()
 }
 
+// FilesystemType returns the FilesystemType for this Filesystem.
+func (fs *Filesystem) FilesystemType() FilesystemType {
+	return fs.fsType
+}
+
 // VirtualFilesystem returns the containing VirtualFilesystem.
 func (fs *Filesystem) VirtualFilesystem() *VirtualFilesystem {
 	return fs.vfs
diff --git a/pkg/sentry/vfs/filesystem_type.go b/pkg/sentry/vfs/filesystem_type.go
index bb9cada81..f2298f7f6 100644
--- a/pkg/sentry/vfs/filesystem_type.go
+++ b/pkg/sentry/vfs/filesystem_type.go
@@ -30,6 +30,9 @@ type FilesystemType interface {
 	// along with its mount root. A reference is taken on the returned
 	// Filesystem and Dentry.
 	GetFilesystem(ctx context.Context, vfsObj *VirtualFilesystem, creds *auth.Credentials, source string, opts GetFilesystemOptions) (*Filesystem, *Dentry, error)
+
+	// Name returns the name of this FilesystemType.
+	Name() string
 }
 
 // GetFilesystemOptions contains options to FilesystemType.GetFilesystem.
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 1708c1a53..720b90d8f 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -134,7 +134,7 @@ func (vfs *VirtualFilesystem) Init() error {
 	anonfs := anonFilesystem{
 		devMinor: anonfsDevMinor,
 	}
-	anonfs.vfsfs.Init(vfs, &anonfs)
+	anonfs.vfsfs.Init(vfs, &anonFilesystemType{}, &anonfs)
 	defer anonfs.vfsfs.DecRef()
 	anonMount, err := vfs.NewDisconnectedMount(&anonfs.vfsfs, nil, &MountOptions{})
 	if err != nil {