Re: [PATCH 06/20] drbd: add RDMA transport implementation

[Leon Romanovsky]

On Wed, Apr 08, 2026 at 02:01:43PM +0200, Christoph Böhmwalder wrote:
> On Tue, Apr 07, 2026 at 10:42:55PM -0700, Christoph Hellwig wrote:
> > You really need to add the RDMA mailing list before adding new RDMA
> > code.  I'll try to review the bits I still remember, but you also
> > need a maintainer ACK.
> 
> Thanks for the hint and your detailed feedback. I'll address all that
> in v2 (plus some other similar fixes).

Thanks Christoph for adding us.
I fast-forward read the patch and immediately spotted two things:
1. Please don't call directly to HW drivers.
+	err = device->ops.query_device(device, &dev_attr, &uhw);
+	if (err) {
+		tr_err(transport, "ib_query_device: %d\n", err);
+		return err;
+	}

2. Add any missing API to RDMA subsystem, don't leave it to the users:
+	} else if (reduced) {
+		/* ib_create_qp() may return -ENOMEM if max_send_wr or max_recv_wr are
+		   too big. Unfortunately there is no way to find the working maxima.
+		   http://www.rdmamojo.com/2012/12/21/ibv_create_qp/
+		   Suggests "Trial end error" to find the maximal number. */
+
+		tr_warn(transport, "Needed to adjust buffer sizes for HCA\n");
+		tr_warn(transport, "rcvbuf = %d sndbuf = %d \n",
+			path->flow[DATA_STREAM].rx_descs_max * DRBD_SOCKET_BUFFER_SIZE,
+			path->flow[DATA_STREAM].tx_descs_max * DRBD_SOCKET_BUFFER_SIZE);
+		tr_warn(transport, "It is recommended to apply this change to the configuration\n");
+	}
+

Thanks


> 
> Thanks,
> Christoph