lib/net: give an informative error when not enough queues

While tuning the number of instances of the functional blocks,
the configuration may exceed the maximum number of queues that
the NICs support. When this happens, the error message in the log
is not informative. For example:

Ethdev port_id=0 nb_rx_queues=43 > 8
Main/0 2024-06-25 17:07:22 ERR init_iface(back): failed to configure interface (errno=22): Invalid argument

This commit identifies the problem and gives a helpful error message:

Main/0 2024-06-25 17:38:22 ERR check_if_queues(back): the current configuration requires 43 RX queues, but the interface supports at most 8 RX queues. It may be possible to reduce the number of instances of the GK or GT functional block to reduce the number of queues. If not, more capable NICs are needed.
Main/0 2024-06-25 17:38:22 ERR init_iface(back): interface doesn't support a critical hardware capability (errno=28): No space left on device

This commit closes #620.

lib/net.c

@@ -1141,6 +1141,42 @@ randomize_rss_key(struct gatekeeper_if *iface)
 	return 0;
 }
 
+static int
+check_if_queues(struct gatekeeper_if *iface,
+	const struct rte_eth_dev_info *dev_info, struct rte_eth_conf *port_conf)
+{
+	const char *type_queues;
+	unsigned int requested_queues, max_queues;
+
+	/*
+	 * DPDK API quirk: rte_eth_dev_configure() receives the numbers of
+	 * RX and TX queues as parameters instead of fields in @port_conf.
+	 */
+	RTE_SET_USED(port_conf);
+
+	if (unlikely(iface->num_rx_queues > dev_info->max_rx_queues)) {
+		type_queues = "RX";
+		requested_queues = iface->num_rx_queues;
+		max_queues = dev_info->max_rx_queues;
+		goto error;
+	}
+
+	if (unlikely(iface->num_tx_queues > dev_info->max_tx_queues)) {
+		type_queues = "TX";
+		requested_queues = iface->num_tx_queues;
+		max_queues = dev_info->max_tx_queues;
+		goto error;
+	}
+
+	return 0;
+
+error:
+	G_LOG(ERR, "%s(%s): the current configuration requires %u %s queues, but the interface supports at most %u %s queues. It may be possible to reduce the number of instances of the GK or GT functional block to reduce the number of queues. If not, more capable NICs are needed.\n",
+		__func__, iface->name, requested_queues, type_queues,
+		max_queues, type_queues);
+	return -ENOSPC;
+}
+
 /*
  * Split up RTE_ETH_RSS_IP into IPv4-related and IPv6-related hash functions.
  * For each type of IP being used in Gatekeeper, check the supported
@@ -1435,6 +1471,10 @@ check_if_offloads(struct gatekeeper_if *iface, struct rte_eth_conf *port_conf)
 		return ret;
 	}
 
+	ret = check_if_queues(iface, &dev_info, port_conf);
+	if (unlikely(ret < 0))
+		return ret;
+
 	ret = check_if_rss(iface, &dev_info, port_conf);
 	if (unlikely(ret < 0))
 		return ret;