IB/iser: New receive buffer posting logic

Currently, the recv buffer posting logic is based on the transactional
nature of iSER which allows for posting a buffer before sending a PDU.
Change this to post only when the number of outstanding recv buffers
is below a water mark and in a batched manner, thus simplifying and
optimizing the data path.  Use a pre-allocated ring of recv buffers
instead of allocating from kmem cache.  A special treatment is given
to the login response buffer whose size must be 8K unlike the size of
buffers used for any other purpose which is 128 bytes.

Signed-off-by: Or Gerlitz <ogerlitz@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c b/drivers/infiniband/ulp/iser/iscsi_iser.c
index 5f7a6fc..355470e 100644
--- a/drivers/infiniband/ulp/iser/iscsi_iser.c
+++ b/drivers/infiniband/ulp/iser/iscsi_iser.c
@@ -283,7 +283,7 @@
 	 * due to issues with the login code re iser sematics
 	 * this not set in iscsi_conn_setup - FIXME
 	 */
-	conn->max_recv_dlength = 128;
+	conn->max_recv_dlength = ISER_RECV_DATA_SEG_LEN;
 
 	iser_conn = conn->dd_data;
 	conn->dd_data = iser_conn;