dm: rename map_info flush_request to target_request_nr

'target_request_nr' is a more generic name that reflects the fact that
it will be used for both flush and discard support.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 1381cd9..531a6f2 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -22,7 +22,7 @@
 union map_info {
 	void *ptr;
 	unsigned long long ll;
-	unsigned flush_request;
+	unsigned target_request_nr;
 };
 
 /*
@@ -174,7 +174,7 @@
 	 * A number of zero-length barrier requests that will be submitted
 	 * to the target for the purpose of flushing cache.
 	 *
-	 * The request number will be placed in union map_info->flush_request.
+	 * The request number will be placed in union map_info->target_request_nr.
 	 * It is a responsibility of the target driver to remap these requests
 	 * to the real underlying devices.
 	 */