drbd: New configuration parameters for dealing with network congestion

net {
    on_congestion {block|pull-ahead|disconnect};
    congestion-fill {sectors};
    congestion-extents {al-extents};
}

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index ef44c7a..03a08ba 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -96,6 +96,12 @@
 	OND_SUSPEND_IO
 };
 
+enum drbd_on_congestion {
+	OC_BLOCK,
+	OC_PULL_AHEAD,
+	OC_DISCONNECT,
+};
+
 /* KEEP the order, do not delete or insert. Only append. */
 enum drbd_ret_codes {
 	ERR_CODE_BASE		= 100,
@@ -146,6 +152,7 @@
 	ERR_PERM		= 152,
 	ERR_NEED_APV_93		= 153,
 	ERR_STONITH_AND_PROT_A  = 154,
+	ERR_CONG_NOT_PROTO_A	= 155,
 
 	/* insert new ones above this line */
 	AFTER_LAST_ERR_CODE