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

pkg/sentry/fsimpl/devtmpfs/devtmpfs.go

@@ -42,6 +42,11 @@ type FilesystemType struct {
 	root *vfs.Dentry
 }
 
+// Name implements vfs.FilesystemType.Name.
+func (*FilesystemType) Name() string {
+	return Name
+}
+
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
 func (fst *FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	fst.initOnce.Do(func() {

pkg/sentry/fsimpl/ext/ext.go

@@ -30,6 +30,9 @@ import (
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
+// Name is the name of this filesystem.
+const Name = "ext"
+
 // FilesystemType implements vfs.FilesystemType.
 type FilesystemType struct{}
 
@@ -91,8 +94,13 @@ func isCompatible(sb disklayout.SuperBlock) bool {
 	return true
 }
 
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
-func (FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	// TODO(b/134676337): Ensure that the user is mounting readonly. If not,
 	// EACCESS should be returned according to mount(2). Filesystem independent
 	// flags (like readonly) are currently not available in pkg/sentry/vfs.
@@ -103,7 +111,7 @@ func (FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFile
 	}
 
 	fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
-	fs.vfsfs.Init(vfsObj, &fs)
+	fs.vfsfs.Init(vfsObj, &fsType, &fs)
 	fs.sb, err = readSuperBlock(dev)
 	if err != nil {
 		return nil, nil, err

pkg/sentry/fsimpl/gofer/gofer.go

@@ -199,6 +199,11 @@ const (
 	InteropModeShared
 )
 
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
 func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	mfp := pgalloc.MemoryFileProviderFromContext(ctx)
@@ -374,7 +379,7 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		dentries:       make(map[*dentry]struct{}),
 		specialFileFDs: make(map[*specialFileFD]struct{}),
 	}
-	fs.vfsfs.Init(vfsObj, fs)
+	fs.vfsfs.Init(vfsObj, &fstype, fs)
 
 	// Construct the root dentry.
 	root, err := fs.newDentry(ctx, attachFile, qid, attrMask, &attr)

pkg/sentry/fsimpl/host/host.go

@@ -38,6 +38,19 @@ import (
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
+// filesystemType implements vfs.FilesystemType.
+type filesystemType struct{}
+
+// GetFilesystem implements FilesystemType.GetFilesystem.
+func (filesystemType) GetFilesystem(context.Context, *vfs.VirtualFilesystem, *auth.Credentials, string, vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	panic("cannot instaniate a host filesystem")
+}
+
+// Name implements FilesystemType.Name.
+func (filesystemType) Name() string {
+	return "none"
+}
+
 // filesystem implements vfs.FilesystemImpl.
 type filesystem struct {
 	kernfs.Filesystem
@@ -46,7 +59,7 @@ type filesystem struct {
 // NewMount returns a new disconnected mount in vfsObj that may be passed to ImportFD.
 func NewMount(vfsObj *vfs.VirtualFilesystem) (*vfs.Mount, error) {
 	fs := &filesystem{}
-	fs.Init(vfsObj)
+	fs.Init(vfsObj, &filesystemType{})
 	vfsfs := fs.VFSFilesystem()
 	// NewDisconnectedMount will take an additional reference on vfsfs.
 	defer vfsfs.DecRef()

pkg/sentry/fsimpl/kernfs/kernfs.go

@@ -63,9 +63,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
-// FilesystemType implements vfs.FilesystemType.
-type FilesystemType struct{}
-
 // Filesystem mostly implements vfs.FilesystemImpl for a generic in-memory
 // filesystem. Concrete implementations are expected to embed this in their own
 // Filesystem type.
@@ -138,8 +135,8 @@ func (fs *Filesystem) processDeferredDecRefsLocked() {
 // Init initializes a kernfs filesystem. This should be called from during
 // vfs.FilesystemType.NewFilesystem for the concrete filesystem embedding
 // kernfs.
-func (fs *Filesystem) Init(vfsObj *vfs.VirtualFilesystem) {
-	fs.vfsfs.Init(vfsObj, fs)
+func (fs *Filesystem) Init(vfsObj *vfs.VirtualFilesystem, fsType vfs.FilesystemType) {
+	fs.vfsfs.Init(vfsObj, fsType, fs)
 }
 
 // VFSFilesystem returns the generic vfs filesystem object.

pkg/sentry/fsimpl/kernfs/kernfs_test.go

@@ -187,9 +187,13 @@ func (*dir) NewNode(context.Context, string, vfs.MknodOptions) (*vfs.Dentry, err
 	return nil, syserror.EPERM
 }
 
-func (fst *fsType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opt vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+func (fsType) Name() string {
+	return "kernfs"
+}
+
+func (fst fsType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opt vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	fs := &filesystem{}
-	fs.Init(vfsObj)
+	fs.Init(vfsObj, &fst)
 	root := fst.rootFn(creds, fs)
 	return fs.VFSFilesystem(), root.VFSDentry(), nil
 }

pkg/sentry/fsimpl/proc/filesystem.go

@@ -36,8 +36,13 @@ type FilesystemType struct{}
 
 var _ vfs.FilesystemType = (*FilesystemType)(nil)
 
-// GetFilesystem implements vfs.FilesystemType.
-func (ft *FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
+// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
+func (ft FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	k := kernel.KernelFromContext(ctx)
 	if k == nil {
 		return nil, nil, fmt.Errorf("procfs requires a kernel")
@@ -48,7 +53,7 @@ func (ft *FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virtual
 	}
 
 	procfs := &kernfs.Filesystem{}
-	procfs.VFSFilesystem().Init(vfsObj, procfs)
+	procfs.VFSFilesystem().Init(vfsObj, &ft, procfs)
 
 	var cgroups map[string]string
 	if opts.InternalData != nil {

pkg/sentry/fsimpl/sys/sys.go

@@ -39,10 +39,15 @@ type filesystem struct {
 	kernfs.Filesystem
 }
 
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
-func (FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	fs := &filesystem{}
-	fs.Filesystem.Init(vfsObj)
+	fs.Filesystem.Init(vfsObj, &fsType)
 	k := kernel.KernelFromContext(ctx)
 	maxCPUCores := k.ApplicationCores()
 	defaultSysDirMode := linux.FileMode(0755)

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -63,6 +63,11 @@ type filesystem struct {
 	nextInoMinusOne uint64 // accessed using atomic memory operations
 }
 
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
 func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
 	memFileProvider := pgalloc.MemoryFileProviderFromContext(ctx)
@@ -74,7 +79,7 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		memFile: memFileProvider.MemoryFile(),
 		clock:   clock,
 	}
-	fs.vfsfs.Init(vfsObj, &fs)
+	fs.vfsfs.Init(vfsObj, &fstype, &fs)
 	root := fs.newDentry(fs.newDirectory(creds, 01777))
 	return &fs.vfsfs, &root.vfsd, nil
 }

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().
 //

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

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.

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 {