mount: fix --devname and fusermount: unknown option 'fsname' when mounting via rc

In this commit

f4c40bf79d mount: add --devname to set the device name sent to FUSE for mount display

The --devname parameter was added. However it was soon noticed that
attempting to mount via the rc gave this error:

    mount helper error: fusermount: unknown option 'fsname'
    mount FAILED: fusermount: exit status 1

This was because the DeviceName (and VolumeName) parameter was never
being initialised when the mount was called via the rc.

The fix for this was to refactor the rc interface so it called the
same Mount method as the command line mount which initialised the
DeviceName and VolumeName parameters properly.

This also fixes the cmd/mount tests which were breaking in the same
way but since they aren't normally run on the CI we didn't notice.

Fixes #6044

vfs/vfstest/fs.go

@@ -102,16 +102,15 @@ func RunTests(t *testing.T, useVFS bool, fn mountlib.MountFn) {
 
 // Run holds the remotes for a test run
 type Run struct {
-	os           Oser
-	vfs          *vfs.VFS
-	useVFS       bool // set if we are testing a VFS not a mount
-	mountPath    string
-	fremote      fs.Fs
-	fremoteName  string
-	cleanRemote  func()
-	umountResult <-chan error
-	umountFn     mountlib.UnmountFn
-	skip         bool
+	os          Oser
+	vfs         *vfs.VFS
+	useVFS      bool // set if we are testing a VFS not a mount
+	mnt         *mountlib.MountPoint
+	mountPath   string
+	fremote     fs.Fs
+	fremoteName string
+	cleanRemote func()
+	skip        bool
 }
 
 // run holds the master Run data
@@ -125,8 +124,7 @@ var run *Run
 // Finalise() will tidy them away when done.
 func newRun(useVFS bool) *Run {
 	r := &Run{
-		useVFS:       useVFS,
-		umountResult: make(chan error, 1),
+		useVFS: useVFS,
 	}
 	fstest.Initialise()
 
@@ -173,14 +171,16 @@ func findMountPath() string {
 func (r *Run) mount() {
 	log.Printf("mount %q %q", r.fremote, r.mountPath)
 	var err error
-	r.vfs = vfs.New(r.fremote, &vfsflags.Opt)
-	r.umountResult, r.umountFn, err = mountFn(r.vfs, r.mountPath, &mountlib.Opt)
+	r.mnt = mountlib.NewMountPoint(mountFn, r.mountPath, r.fremote, &mountlib.Opt, &vfsflags.Opt)
+
+	_, err = r.mnt.Mount()
 	if err != nil {
 		log.Printf("mount FAILED: %v", err)
 		r.skip = true
 	} else {
 		log.Printf("mount OK")
 	}
+	r.vfs = r.mnt.VFS
 	if r.useVFS {
 		r.os = vfsOs{r.vfs}
 	} else {
@@ -202,17 +202,17 @@ func (r *Run) umount() {
 		}
 	*/
 	log.Printf("Unmounting %q", r.mountPath)
-	err := r.umountFn()
+	err := r.mnt.Unmount()
 	if err != nil {
 		log.Printf("signal to umount failed - retrying: %v", err)
 		time.Sleep(3 * time.Second)
-		err = r.umountFn()
+		err = r.mnt.Unmount()
 	}
 	if err != nil {
 		log.Fatalf("signal to umount failed: %v", err)
 	}
 	log.Printf("Waiting for umount")
-	err = <-r.umountResult
+	err = <-r.mnt.ErrChan
 	if err != nil {
 		log.Fatalf("umount failed: %v", err)
 	}