Use tmpfs for snapshots

main.go

@@ -183,6 +183,12 @@ func umount(v *ofsVolume, rt *ofsVolumeRt) error {
 					log.WithFields(log.Fields{"name": v.Volume.Name, "snapshot": i}).Trace("Snapshot unmounted on unmount.")
 				}
 			}
+
+			if err := exec.Command("umount", snapshotsPath).Run(); err != nil {
+				log.WithFields(log.Fields{"name": v.Volume.Name}).Warn("Failed to unmount a snapshots tmpfs on unmount.")
+			} else {
+				log.WithFields(log.Fields{"name": v.Volume.Name}).Trace("Snapshot tmpfs unmounted on unmount.")
+			}
 		} else {
 			log.WithFields(log.Fields{"name": v.Volume.Name, "Error": err}).Warn("Cannot determine existing snapshot mounts on unmount")
 		}
@@ -339,6 +345,12 @@ func (d *ofsDriver) Mount(r *volume.MountRequest) (*volume.MountResponse, error)
 					}
 				}
 
+				// Mount a tmpfs there so it becomes machine specific and we can promptly delete directories
+				// that are outside of filteredSnapshots
+				if err := exec.Command("/bin/mount", "-t", "tmpfs", "-o", "size=8m", "tmpfs", snapshotsPath).Run(); err != nil {
+					log.WithFields(log.Fields{"name": r.Name, "directory": snapshotsDirectory}).Warn("Failed to create tmpfs in the snapshots mount directory.")
+				}
+
 				for cmd.ProcessState == nil {
 					if snapshotRulesB, err := applyEnv(exec.Command("/sbin/mount.objectivefs", "snapshot", "-l", v.Fs), v.Env).Output(); err == nil {
 						log.WithFields(log.Fields{"name": r.Name, "snapshotRules": string(snapshotRulesB)}).Debug("Current snapshot rules")
@@ -367,8 +379,6 @@ func (d *ofsDriver) Mount(r *volume.MountRequest) (*volume.MountResponse, error)
 											}
 
 											// Unmount snapshots that are no longer in filteredSnapshots to conserve RAM
-											// Note: We cannot remove the directory as other machines may have different
-											//	filteredSnapshots and may be using them.
 											for i, path := range setMinus(existingMounts, setIntersect(expectedSnapshots, filteredSnapshots)) {
 												if err := exec.Command("umount", path).Run(); err != nil {
 													log.WithFields(log.Fields{"name": r.Name, "snapshot": i}).Warn("Failed to unmount an expired snapshot.")
@@ -378,9 +388,9 @@ func (d *ofsDriver) Mount(r *volume.MountRequest) (*volume.MountResponse, error)
 											}
 
 											// Remove left-over dirs of expired snapshots
-											// Note: That is directories that no other machine would use as the snapshots are not
-											//	mounted due to filteredSnapshots but because they are not even in expectedSnapshots.
-											for i, path := range setMinus(existingMountDirs, expectedSnapshots) {
+											// Note: As our root shall be on tmpfs deleting the directories does not affect
+											//	other machines with different filteredSnapshots
+											for i, path := range setMinus(existingMountDirs, setIntersect(expectedSnapshots, filteredSnapshots)) {
 												if err := os.Remove(path); err != nil {
 													log.WithFields(log.Fields{"name": r.Name, "snapshot": i}).Warn("Failed to remove directory of an expired snapshot.")
 												}