Added stub FUSE filesystem

Allow FUSE filesystems to be mounted using libfuse.
The appropriate flags and mount options are parsed and
understood by fusefs.

1 files changed, 28 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/fuse/dev.go b/pkg/sentry/fsimpl/fuse/dev.go
index dc33268af..c9e12a94f 100644
--- a/pkg/sentry/fsimpl/fuse/dev.go
+++ b/pkg/sentry/fsimpl/fuse/dev.go
@@ -51,6 +51,9 @@ type DeviceFD struct {
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
 
+	// mounted specifies whether a FUSE filesystem was mounted using the DeviceFD.
+	mounted bool
+
 	// TODO(gvisor.dev/issue/2987): Add all the data structures needed to enqueue
 	// and deque requests, control synchronization and establish communication
 	// between the FUSE kernel module and the /dev/fuse character device.
@@ -61,26 +64,51 @@ func (fd *DeviceFD) Release() {}
 
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *DeviceFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	// Operations on /dev/fuse don't make sense until a FUSE filesystem is mounted.
+	if !fd.mounted {
+		return 0, syserror.EPERM
+	}
+
 	return 0, syserror.ENOSYS
 }
 
 // Read implements vfs.FileDescriptionImpl.Read.
 func (fd *DeviceFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	// Operations on /dev/fuse don't make sense until a FUSE filesystem is mounted.
+	if !fd.mounted {
+		return 0, syserror.EPERM
+	}
+
 	return 0, syserror.ENOSYS
 }
 
 // PWrite implements vfs.FileDescriptionImpl.PWrite.
 func (fd *DeviceFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	// Operations on /dev/fuse don't make sense until a FUSE filesystem is mounted.
+	if !fd.mounted {
+		return 0, syserror.EPERM
+	}
+
 	return 0, syserror.ENOSYS
 }
 
 // Write implements vfs.FileDescriptionImpl.Write.
 func (fd *DeviceFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	// Operations on /dev/fuse don't make sense until a FUSE filesystem is mounted.
+	if !fd.mounted {
+		return 0, syserror.EPERM
+	}
+
 	return 0, syserror.ENOSYS
 }
 
 // Seek implements vfs.FileDescriptionImpl.Seek.
 func (fd *DeviceFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	// Operations on /dev/fuse don't make sense until a FUSE filesystem is mounted.
+	if !fd.mounted {
+		return 0, syserror.EPERM
+	}
+
 	return 0, syserror.ENOSYS
 }