Add support for async IO verification offload

This adds support for setting up a number of IO verification offload
threads, instead of doing the offload inline. An option for controlling
the CPU affinity of those threads are always added.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/file.h b/file.h
index 6aa5b50..dc22d4e 100644
--- a/file.h
+++ b/file.h
@@ -133,6 +133,7 @@
 extern int add_file(struct thread_data *, const char *);
 extern void get_file(struct fio_file *);
 extern int __must_check put_file(struct thread_data *, struct fio_file *);
+extern void put_file_log(struct thread_data *, struct fio_file *);
 extern void lock_file(struct thread_data *, struct fio_file *, enum fio_ddir);
 extern void unlock_file(struct thread_data *, struct fio_file *);
 extern void unlock_file_all(struct thread_data *, struct fio_file *);