mount: add -volumeName to name the disk explicitly (#11165)

* mount: let volumeName take an explicit override

volumeName only ever derived the disk's label from -filer.path, -dir,
or the filer address, so a name that happened to collide with
something else - e.g. a UNC share's own name - could not be changed
without moving what was mounted. Give it an override parameter that
wins over all three; nothing passes one yet.

* mount: add -volumeName to name the disk explicitly

Windows has no equivalent of the "weed fuse" -o passthrough that lets
a Linux or macOS mount override its derived volname, so a name picked
up from -dir - e.g. a UNC share's own name - could not be changed
short of moving what was mounted. -volumeName overrides it on every
platform.

* mount: document -volumeName

* mount: scope -volumeName's help text to macOS and Windows

Linux has no volume-label mount option for -volumeName to feed, so
the flag's own description says where it applies instead of leaving
that unstated.

* mount: forward -volumeName through the weed fuse option parser

weed fuse (the /etc/fstab helper) turns -o key=value into the same
MountOptions weed mount takes, but volumeName had no case, so it fell
through to being forwarded as a literal, unrecognized FUSE option
instead of ever reaching mountOptions.volumeName.

* mount: apply -volumeName to FsName on Linux and FreeBSD

FsName only ever took the filer address and -filer.path, so
-volumeName had nothing to override there and silently did nothing;
the skipAutofs case still forces "fuse", since that name is what
util-linux/mount requires to recognize the pseudo filesystem.

weed/command/fuse_std_test.go

@@ -36,3 +36,32 @@ func TestRunFuseDoesNotSkipOptionAfterConcurrentWriters(t *testing.T) {
 		"child=1,concurrentWriters=2,concurrentReaders=bad,umask=bad",
 	})
 }
+
+func TestRunFuseSetsVolumeName(t *testing.T) {
+	oldVolumeName := mountOptions.volumeName
+	oldConcurrentReaders := mountOptions.concurrentReaders
+	oldDir := mountOptions.dir
+	defer func() {
+		gotVolumeName := mountOptions.volumeName
+		mountOptions.volumeName = oldVolumeName
+		mountOptions.concurrentReaders = oldConcurrentReaders
+		mountOptions.dir = oldDir
+
+		recovered := recover()
+		if recovered == nil {
+			t.Fatal("expected invalid concurrentReaders option to be parsed")
+		}
+		if gotVolumeName == nil {
+			t.Fatal("expected -o volumeName=MyDisk to set mountOptions.volumeName, got nil")
+		}
+		if *gotVolumeName != "MyDisk" {
+			t.Fatalf("expected -o volumeName=MyDisk to set mountOptions.volumeName, got %q", *gotVolumeName)
+		}
+	}()
+
+	runFuse(cmdMount, []string{
+		"/mnt",
+		"-o",
+		"volumeName=MyDisk,concurrentReaders=bad",
+	})
+}