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/os/os-linux.h b/os/os-linux.h
index b766cbf..dd9c5aa 100644
--- a/os/os-linux.h
+++ b/os/os-linux.h
@@ -55,13 +55,13 @@
  * the affinity helpers to work.
  */
 #ifndef GLIBC_2_3_2
-#define fio_setaffinity(td)		\
-	sched_setaffinity((td)->pid, sizeof((td)->o.cpumask), &(td)->o.cpumask)
+#define fio_setaffinity(pid, cpumask)		\
+	sched_setaffinity((pid), sizeof(cpumask), &(cpumask))
 #define fio_getaffinity(pid, ptr)	\
 	sched_getaffinity((pid), sizeof(cpu_set_t), (ptr))
 #else
-#define fio_setaffinity(td)		\
-	sched_setaffinity((td)->pid, &(td)->o.cpumask)
+#define fio_setaffinity(pid, cpumask)	\
+	sched_setaffinity((pid), &(cpumask))
 #define fio_getaffinity(pid, ptr)	\
 	sched_getaffinity((pid), (ptr))
 #endif