smb: server: correct value for smb_direct_max_fragmented_recv_size

We should make it clear that we use this strange value
instead of hiding it in same code flow.

Note this value is mainly ignored currently,
as we do the calculation again with
the negotiated max_recv_size in smb_direct_prepare().
So this is only a cosmetic change in order to
avoid confusion.

In future we may change the logic and
adjust the number of recv buffers instead
of the max_fragmented_recv_size.

Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: metze-samba

fs/smb/server/transport_rdma.c

@@ -70,8 +70,23 @@ static int smb_direct_send_credit_target = 255;
 /* The maximum single message size can be sent to remote peer */
 static int smb_direct_max_send_size = 1364;
 
-/*  The maximum fragmented upper-layer payload receive size supported */
-static int smb_direct_max_fragmented_recv_size = 1024 * 1024;
+/*
+ * The maximum fragmented upper-layer payload receive size supported
+ *
+ * Assume max_payload_per_credit is
+ * smb_direct_receive_credit_max - 24 = 1340
+ *
+ * The maximum number would be
+ * smb_direct_receive_credit_max * max_payload_per_credit
+ *
+ *                       1340 * 255 = 341700 (0x536C4)
+ *
+ * The minimum value from the spec is 131072 (0x20000)
+ *
+ * For now we use the logic we used before:
+ *                 (1364 * 255) / 2 = 173910 (0x2A756)
+ */
+static int smb_direct_max_fragmented_recv_size = (1364 * 255) / 2;
 
 /*  The maximum single-message size which can be received */
 static int smb_direct_max_receive_size = 1364;
@@ -2531,6 +2546,29 @@ static int smb_direct_prepare(struct ksmbd_transport *t)
 				  le32_to_cpu(req->max_receive_size));
 	sp->max_fragmented_send_size =
 		le32_to_cpu(req->max_fragmented_size);
+	/*
+	 * The maximum fragmented upper-layer payload receive size supported
+	 *
+	 * Assume max_payload_per_credit is
+	 * smb_direct_receive_credit_max - 24 = 1340
+	 *
+	 * The maximum number would be
+	 * smb_direct_receive_credit_max * max_payload_per_credit
+	 *
+	 *                       1340 * 255 = 341700 (0x536C4)
+	 *
+	 * The minimum value from the spec is 131072 (0x20000)
+	 *
+	 * For now we use the logic we used before:
+	 *                 (1364 * 255) / 2 = 173910 (0x2A756)
+	 *
+	 * We need to adjust this here in case the peer
+	 * lowered sp->max_recv_size.
+	 *
+	 * TODO: instead of adjusting max_fragmented_recv_size
+	 * we should adjust the number of available buffers,
+	 * but for now we keep the current logic.
+	 */
 	sp->max_fragmented_recv_size =
 		(sp->recv_credit_max * sp->max_recv_size) / 2;
 	sc->recv_io.credits.target = le16_to_cpu(req->credits_requested);