Add support for write_iops_log

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/iolog.h b/iolog.h
index dd4d647..d8140f2 100644
--- a/iolog.h
+++ b/iolog.h
@@ -93,6 +93,7 @@
 				unsigned int);
 extern void add_bw_sample(struct thread_data *, enum fio_ddir, unsigned int,
 				struct timeval *);
+extern void add_iops_sample(struct thread_data *, enum fio_ddir, struct timeval *);
 extern void show_run_stats(void);
 extern void init_disk_util(struct thread_data *);
 extern void update_rusage_stat(struct thread_data *);