From b4820e598681c61fbf0e8a7f4d3436d2599ce53c Mon Sep 17 00:00:00 2001
From: Rahat Mahmood <rahat@google.com>
Date: Fri, 28 Aug 2020 14:29:16 -0700
Subject: Implement StatFS for various VFS2 filesystems.

This mainly involved enabling kernfs' client filesystems to provide a
StatFS implementation.

Fixes #3411, #3515.

PiperOrigin-RevId: 329009864
---
 pkg/sentry/fsimpl/devpts/devpts.go             | 10 +++++++++-
 pkg/sentry/fsimpl/devpts/master.go             |  1 +
 pkg/sentry/fsimpl/devpts/slave.go              |  1 +
 pkg/sentry/fsimpl/fuse/fusefs.go               |  8 +++++++-
 pkg/sentry/fsimpl/host/host.go                 |  1 +
 pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go |  1 +
 pkg/sentry/fsimpl/kernfs/filesystem.go         |  5 ++---
 pkg/sentry/fsimpl/kernfs/inode_impl_util.go    | 16 +++++++++++++---
 pkg/sentry/fsimpl/kernfs/kernfs.go             |  5 +++++
 pkg/sentry/fsimpl/kernfs/kernfs_test.go        |  8 +++++---
 pkg/sentry/fsimpl/kernfs/symlink.go            |  1 +
 pkg/sentry/fsimpl/pipefs/pipefs.go             |  8 +++++---
 pkg/sentry/fsimpl/proc/filesystem.go           |  7 +++++++
 pkg/sentry/fsimpl/proc/subtasks.go             |  9 +++++----
 pkg/sentry/fsimpl/proc/task.go                 |  7 ++++---
 pkg/sentry/fsimpl/proc/task_fds.go             | 19 +++++++++++--------
 pkg/sentry/fsimpl/proc/task_files.go           |  2 ++
 pkg/sentry/fsimpl/proc/tasks.go                |  9 +++++----
 pkg/sentry/fsimpl/proc/tasks_files.go          |  2 ++
 pkg/sentry/fsimpl/sockfs/sockfs.go             |  9 +++++++--
 pkg/sentry/fsimpl/sys/kcov.go                  |  3 ++-
 pkg/sentry/fsimpl/sys/sys.go                   | 14 ++++++++++++++
 22 files changed, 110 insertions(+), 36 deletions(-)

(limited to 'pkg/sentry/fsimpl')

diff --git a/pkg/sentry/fsimpl/devpts/devpts.go b/pkg/sentry/fsimpl/devpts/devpts.go
index 0eaff9087..57580f4d4 100644
--- a/pkg/sentry/fsimpl/devpts/devpts.go
+++ b/pkg/sentry/fsimpl/devpts/devpts.go
@@ -111,12 +111,13 @@ func (fs *filesystem) Release(ctx context.Context) {
 
 // rootInode is the root directory inode for the devpts mounts.
 type rootInode struct {
-	rootInodeRefs
+	implStatFS
 	kernfs.AlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
+	rootInodeRefs
 
 	locks vfs.FileLocks
 
@@ -240,3 +241,10 @@ func (i *rootInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback,
 func (i *rootInode) DecRef(context.Context) {
 	i.rootInodeRefs.DecRef(i.Destroy)
 }
+
+type implStatFS struct{}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.DEVPTS_SUPER_MAGIC), nil
+}
diff --git a/pkg/sentry/fsimpl/devpts/master.go b/pkg/sentry/fsimpl/devpts/master.go
index 3bb397f71..60feb1993 100644
--- a/pkg/sentry/fsimpl/devpts/master.go
+++ b/pkg/sentry/fsimpl/devpts/master.go
@@ -30,6 +30,7 @@ import (
 
 // masterInode is the inode for the master end of the Terminal.
 type masterInode struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
diff --git a/pkg/sentry/fsimpl/devpts/slave.go b/pkg/sentry/fsimpl/devpts/slave.go
index 32e4e1908..a9da7af64 100644
--- a/pkg/sentry/fsimpl/devpts/slave.go
+++ b/pkg/sentry/fsimpl/devpts/slave.go
@@ -29,6 +29,7 @@ import (
 
 // slaveInode is the inode for the slave end of the Terminal.
 type slaveInode struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index 9717c0e15..810819ae4 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -200,9 +200,9 @@ func (fs *filesystem) Release(ctx context.Context) {
 type inode struct {
 	inodeRefs
 	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNoDynamicLookup
 	kernfs.InodeNotSymlink
-	kernfs.InodeDirectoryNoNewChildren
 	kernfs.OrderedChildren
 
 	locks vfs.FileLocks
@@ -331,3 +331,9 @@ func (i *inode) Stat(ctx context.Context, fs *vfs.Filesystem, opts vfs.StatOptio
 func (i *inode) DecRef(context.Context) {
 	i.inodeRefs.DecRef(i.Destroy)
 }
+
+// StatFS implements kernfs.Inode.StatFS.
+func (i *inode) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
+	// TODO(gvisor.dev/issues/3413): Complete the implementation of statfs.
+	return vfs.GenericStatFS(linux.FUSE_SUPER_MAGIC), nil
+}
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 2d3821f33..7561f821c 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -186,6 +186,7 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 
 // inode implements kernfs.Inode.
 type inode struct {
+	kernfs.InodeNoStatFS
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 
diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index 12adf727a..1ee089620 100644
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
@@ -35,6 +35,7 @@ import (
 // +stateify savable
 type DynamicBytesFile struct {
 	InodeAttrs
+	InodeNoStatFS
 	InodeNoopRefCount
 	InodeNotDirectory
 	InodeNotSymlink
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index e5d6b5c35..0e3011689 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -721,14 +721,13 @@ func (fs *Filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 // StatFSAt implements vfs.FilesystemImpl.StatFSAt.
 func (fs *Filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linux.Statfs, error) {
 	fs.mu.RLock()
-	_, _, err := fs.walkExistingLocked(ctx, rp)
+	_, inode, err := fs.walkExistingLocked(ctx, rp)
 	fs.mu.RUnlock()
 	fs.processDeferredDecRefs(ctx)
 	if err != nil {
 		return linux.Statfs{}, err
 	}
-	// TODO(gvisor.dev/issue/1193): actually implement statfs.
-	return linux.Statfs{}, syserror.ENOSYS
+	return inode.StatFS(ctx, fs.VFSFilesystem())
 }
 
 // SymlinkAt implements vfs.FilesystemImpl.SymlinkAt.
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index f442a5606..c0b863ba4 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -546,12 +546,13 @@ func (InodeSymlink) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.D
 //
 // +stateify savable
 type StaticDirectory struct {
-	StaticDirectoryRefs
-	InodeNotSymlink
-	InodeDirectoryNoNewChildren
 	InodeAttrs
+	InodeDirectoryNoNewChildren
 	InodeNoDynamicLookup
+	InodeNoStatFS
+	InodeNotSymlink
 	OrderedChildren
+	StaticDirectoryRefs
 
 	locks  vfs.FileLocks
 	fdOpts GenericDirectoryFDOptions
@@ -609,3 +610,12 @@ type AlwaysValid struct{}
 func (*AlwaysValid) Valid(context.Context) bool {
 	return true
 }
+
+// InodeNoStatFS partially implements the Inode interface, where the client
+// filesystem doesn't support statfs(2).
+type InodeNoStatFS struct{}
+
+// StatFS implements Inode.StatFS.
+func (*InodeNoStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return linux.Statfs{}, syserror.ENOSYS
+}
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index ca3685800..88fcd54aa 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -320,6 +320,11 @@ type Inode interface {
 	// Precondition: rp.Done(). vfsd.Impl() must be the kernfs Dentry containing
 	// the inode on which Open() is being called.
 	Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error)
+
+	// StatFS returns filesystem statistics for the client filesystem. This
+	// corresponds to vfs.FilesystemImpl.StatFSAt. If the client filesystem
+	// doesn't support statfs(2), this should return ENOSYS.
+	StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error)
 }
 
 type inodeRefs interface {
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_test.go b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
index e376d1736..675587c6b 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_test.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
@@ -98,9 +98,10 @@ func (*attrs) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.S
 type readonlyDir struct {
 	readonlyDirRefs
 	attrs
-	kernfs.InodeNotSymlink
-	kernfs.InodeNoDynamicLookup
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNoDynamicLookup
+	kernfs.InodeNoStatFS
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
 
 	locks vfs.FileLocks
@@ -137,9 +138,10 @@ func (d *readonlyDir) DecRef(context.Context) {
 type dir struct {
 	dirRefs
 	attrs
-	kernfs.InodeNotSymlink
 	kernfs.InodeNoDynamicLookup
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
+	kernfs.InodeNoStatFS
 
 	locks vfs.FileLocks
 
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index 2ab3f53fd..64731a3e4 100644
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
@@ -28,6 +28,7 @@ type StaticSymlink struct {
 	InodeAttrs
 	InodeNoopRefCount
 	InodeSymlink
+	InodeNoStatFS
 
 	target string
 }
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs.go b/pkg/sentry/fsimpl/pipefs/pipefs.go
index 2ca793db9..7053ad6db 100644
--- a/pkg/sentry/fsimpl/pipefs/pipefs.go
+++ b/pkg/sentry/fsimpl/pipefs/pipefs.go
@@ -143,14 +143,16 @@ func (i *inode) SetStat(ctx context.Context, vfsfs *vfs.Filesystem, creds *auth.
 	return syserror.EPERM
 }
 
-// TODO(gvisor.dev/issue/1193): kernfs does not provide a way to implement
-// statfs, from which we should indicate PIPEFS_MAGIC.
-
 // Open implements kernfs.Inode.Open.
 func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
 	return i.pipe.Open(ctx, rp.Mount(), vfsd, opts.Flags, &i.locks)
 }
 
+// StatFS implements kernfs.Inode.StatFS.
+func (i *inode) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.PIPEFS_MAGIC), nil
+}
+
 // NewConnectedPipeFDs returns a pair of FileDescriptions representing the read
 // and write ends of a newly-created pipe, as for pipe(2) and pipe2(2).
 //
diff --git a/pkg/sentry/fsimpl/proc/filesystem.go b/pkg/sentry/fsimpl/proc/filesystem.go
index c350ec127..03b5941b9 100644
--- a/pkg/sentry/fsimpl/proc/filesystem.go
+++ b/pkg/sentry/fsimpl/proc/filesystem.go
@@ -121,3 +121,10 @@ func newStaticDir(creds *auth.Credentials, devMajor, devMinor uint32, ino uint64
 type InternalData struct {
 	Cgroups map[string]string
 }
+
+type implStatFS struct{}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.PROC_SUPER_MAGIC), nil
+}
diff --git a/pkg/sentry/fsimpl/proc/subtasks.go b/pkg/sentry/fsimpl/proc/subtasks.go
index 01c0efb3a..d57d94dbc 100644
--- a/pkg/sentry/fsimpl/proc/subtasks.go
+++ b/pkg/sentry/fsimpl/proc/subtasks.go
@@ -31,12 +31,13 @@ import (
 //
 // +stateify savable
 type subtasksInode struct {
-	subtasksInodeRefs
-	kernfs.InodeNotSymlink
-	kernfs.InodeDirectoryNoNewChildren
+	implStatFS
+	kernfs.AlwaysValid
 	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
-	kernfs.AlwaysValid
+	subtasksInodeRefs
 
 	locks vfs.FileLocks
 
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index 66b557abd..dbdb5d929 100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
@@ -32,12 +32,13 @@ import (
 //
 // +stateify savable
 type taskInode struct {
-	taskInodeRefs
-	kernfs.InodeNotSymlink
+	implStatFS
+	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNoDynamicLookup
-	kernfs.InodeAttrs
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
+	taskInodeRefs
 
 	locks vfs.FileLocks
 
diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
index 0527b2de8..3f0d78461 100644
--- a/pkg/sentry/fsimpl/proc/task_fds.go
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
@@ -100,13 +100,14 @@ func (i *fdDir) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, off
 //
 // +stateify savable
 type fdDirInode struct {
+	fdDir
 	fdDirInodeRefs
-	kernfs.InodeNotSymlink
-	kernfs.InodeDirectoryNoNewChildren
+	implStatFS
+	kernfs.AlwaysValid
 	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
-	kernfs.AlwaysValid
-	fdDir
 }
 
 var _ kernfs.Inode = (*fdDirInode)(nil)
@@ -185,6 +186,7 @@ func (i *fdDirInode) DecRef(context.Context) {
 //
 // +stateify savable
 type fdSymlink struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeSymlink
@@ -233,13 +235,14 @@ func (s *fdSymlink) Getlink(ctx context.Context, mnt *vfs.Mount) (vfs.VirtualDen
 //
 // +stateify savable
 type fdInfoDirInode struct {
+	fdDir
 	fdInfoDirInodeRefs
-	kernfs.InodeNotSymlink
-	kernfs.InodeDirectoryNoNewChildren
+	implStatFS
+	kernfs.AlwaysValid
 	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
-	kernfs.AlwaysValid
-	fdDir
 }
 
 var _ kernfs.Inode = (*fdInfoDirInode)(nil)
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index 830b78949..356036b9b 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -648,6 +648,7 @@ func (o *oomScoreAdj) Write(ctx context.Context, src usermem.IOSequence, offset
 //
 // +stateify savable
 type exeSymlink struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeSymlink
@@ -832,6 +833,7 @@ func (s *namespaceSymlink) Getlink(ctx context.Context, mnt *vfs.Mount) (vfs.Vir
 // namespaceInode is a synthetic inode created to represent a namespace in
 // /proc/[pid]/ns/*.
 type namespaceInode struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
diff --git a/pkg/sentry/fsimpl/proc/tasks.go b/pkg/sentry/fsimpl/proc/tasks.go
index 863c4467e..3ea00ab87 100644
--- a/pkg/sentry/fsimpl/proc/tasks.go
+++ b/pkg/sentry/fsimpl/proc/tasks.go
@@ -37,12 +37,13 @@ const (
 //
 // +stateify savable
 type tasksInode struct {
-	tasksInodeRefs
-	kernfs.InodeNotSymlink
-	kernfs.InodeDirectoryNoNewChildren
+	implStatFS
+	kernfs.AlwaysValid
 	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
-	kernfs.AlwaysValid
+	tasksInodeRefs
 
 	locks vfs.FileLocks
 
diff --git a/pkg/sentry/fsimpl/proc/tasks_files.go b/pkg/sentry/fsimpl/proc/tasks_files.go
index 7d8983aa5..8c41729e4 100644
--- a/pkg/sentry/fsimpl/proc/tasks_files.go
+++ b/pkg/sentry/fsimpl/proc/tasks_files.go
@@ -32,6 +32,7 @@ import (
 )
 
 type selfSymlink struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeSymlink
@@ -74,6 +75,7 @@ func (*selfSymlink) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials,
 }
 
 type threadSelfSymlink struct {
+	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeSymlink
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
index c61818ff6..94a998568 100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -81,10 +81,10 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 
 // inode implements kernfs.Inode.
 type inode struct {
-	kernfs.InodeNotDirectory
-	kernfs.InodeNotSymlink
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
 }
 
 // Open implements kernfs.Inode.Open.
@@ -92,6 +92,11 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentr
 	return nil, syserror.ENXIO
 }
 
+// StatFS implements kernfs.Inode.StatFS.
+func (i *inode) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.SOCKFS_MAGIC), nil
+}
+
 // NewDentry constructs and returns a sockfs dentry.
 //
 // Preconditions: mnt.Filesystem() must have been returned by NewFilesystem().
diff --git a/pkg/sentry/fsimpl/sys/kcov.go b/pkg/sentry/fsimpl/sys/kcov.go
index 92710d877..73f3d3309 100644
--- a/pkg/sentry/fsimpl/sys/kcov.go
+++ b/pkg/sentry/fsimpl/sys/kcov.go
@@ -39,8 +39,9 @@ func (fs *filesystem) newKcovFile(ctx context.Context, creds *auth.Credentials)
 type kcovInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
-	kernfs.InodeNotSymlink
 	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+	implStatFS
 }
 
 func (i *kcovInode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index ea30a4ec2..39952d2d0 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -163,9 +163,16 @@ func (d *dir) DecRef(context.Context) {
 	d.dirRefs.DecRef(d.Destroy)
 }
 
+// StatFS implements kernfs.Inode.StatFS.
+func (d *dir) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.SYSFS_MAGIC), nil
+}
+
 // cpuFile implements kernfs.Inode.
 type cpuFile struct {
+	implStatFS
 	kernfs.DynamicBytesFile
+
 	maxCores uint
 }
 
@@ -182,3 +189,10 @@ func (fs *filesystem) newCPUFile(creds *auth.Credentials, maxCores uint, mode li
 	d.Init(c)
 	return d
 }
+
+type implStatFS struct{}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.SYSFS_MAGIC), nil
+}
-- 
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