AF_XDP-interaction: Implement ethtool_get_max_queues

Need to get configured queues on the NIC device

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

AF_XDP-interaction/ethtool_utils.c

@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+#include <net/if.h>
+#include <sys/ioctl.h>
+#include <linux/ethtool.h>
+#include <linux/sockios.h>
+#ifndef SIOCETHTOOL
+#define SIOCETHTOOL	0x8946		/* Ethtool interface		*/
+#endif
+
+#include <errno.h>
+#include <string.h> /* memcpy */
+#include <unistd.h> /* close */
+
+#ifndef max
+# define max(x, y) ((x) < (y) ? (y) : (x))
+#endif
+
+
+/* Based on xsk_get_max_queues(), but needed info on max_queues before
+ * xsk objects are created.
+ */
+int ethtool_get_max_queues(const char *ifname)
+{
+	struct ethtool_channels channels = { .cmd = ETHTOOL_GCHANNELS };
+	struct ifreq ifr = {};
+	int fd, err, ret;
+
+	fd = socket(AF_LOCAL, SOCK_DGRAM | SOCK_CLOEXEC, 0);
+	if (fd < 0)
+		return -errno;
+
+	ifr.ifr_data = (void *)&channels;
+	memcpy(ifr.ifr_name, ifname, IFNAMSIZ - 1);
+	ifr.ifr_name[IFNAMSIZ - 1] = '\0';
+	err = ioctl(fd, SIOCETHTOOL, &ifr);
+	if (err && errno != EOPNOTSUPP) {
+		ret = -errno;
+		goto out;
+	}
+
+	if (err) {
+		/* If the device says it has no channels, then all traffic
+		 * is sent to a single stream, so max queues = 1.
+		 */
+		ret = 1;
+	} else {
+		/* Take the max of rx, tx, combined. Drivers return
+		 * the number of channels in different ways.
+		 */
+		ret = max(channels.max_rx, channels.max_tx);
+		ret = max(ret, (int)channels.max_combined);
+	}
+
+out:
+	close(fd);
+	return ret;
+}