lxd/fsmonitor: Add constants for driver names.

Signed-off-by: Mark Laing <mark.laing@canonical.com>

lxd/fsmonitor/fsmonitor_interface.go

@@ -1,5 +1,17 @@
 package fsmonitor
 
+const (
+	// DriverNameFANotify is the name of the FANotify driver.
+	//
+	// FANotify should be preferred over INotify because it is more performant and does not need to recursively watch
+	// subdirectories. However, it is not possible to use fanotify if the specified path is not a mountpoint because we
+	// need to use the unix.FAN_MARK_FILESYSTEM flag for this functionality.
+	DriverNameFANotify = "fanotify"
+
+	// DriverNameINotify is the name of the inotify driver.
+	DriverNameINotify = "inotify"
+)
+
 // FSMonitor represents a filesystem monitor.
 type FSMonitor interface {
 	DriverName() string