Implement StatFS for various VFS2 filesystems.

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

Fixes #3411, #3515.

PiperOrigin-RevId: 329009864

6 files changed, 27 insertions, 9 deletions

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
 }