netdev - [RFC PATCH bpf-next 2/4] libbpf: check for channels.max_{t,r}x in xsk_get_max

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Message-Id: <20190603131907.13395-3-maciej.fijalkowski@intel.com>
Date:   Mon,  3 Jun 2019 15:19:05 +0200
From:   Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
To:     magnus.karlsson@...el.com, bjorn.topel@...el.com,
        netdev@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, jakub.kicinski@...ronome.com,
        jonathan.lemon@...il.com, songliubraving@...com
Subject: [RFC PATCH bpf-next 2/4] libbpf: check for channels.max_{t,r}x in xsk_get_max_queues

When it comes down to ethtool's get channels API, various drivers are
reporting the queue count in two ways - they are setting max_combined or
max_tx/max_rx fields. When creating the eBPF maps for xsk socket, this
API is used so that we have an entries in maps per each queue.
In case where driver (mlx4, ice) reports queues in max_tx/max_rx, we end
up with eBPF maps with single entries, so it's not possible to attach an
AF_XDP socket onto queue other than 0 - xsk_set_bpf_maps() would try to
call bpf_map_update_elem() with key set to xsk->queue_id.

To fix this, let's look for channels.max_{t,r}x as well in
xsk_get_max_queues.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
---
 tools/lib/bpf/xsk.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 57dda1389870..514ab3fb06f4 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -339,21 +339,23 @@ static int xsk_get_max_queues(struct xsk_socket *xsk)
 	ifr.ifr_data = (void *)&channels;
 	strncpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ);
 	err = ioctl(fd, SIOCETHTOOL, &ifr);
-	if (err && errno != EOPNOTSUPP) {
-		ret = -errno;
-		goto out;
-	}
+	close(fd);
+
+	if (err && errno != EOPNOTSUPP)
+		return -errno;
 
-	if (channels.max_combined == 0 || errno == EOPNOTSUPP)
+	if (channels.max_combined)
+		ret = channels.max_combined;
+	else if (channels.max_rx && channels.max_tx)
+		ret = min(channels.max_rx, channels.max_tx);
+	else if (channels.max_combined == 0 || errno == EOPNOTSUPP)
 		/* If the device says it has no channels, then all traffic
 		 * is sent to a single stream, so max queues = 1.
 		 */
 		ret = 1;
 	else
-		ret = channels.max_combined;
+		ret = -1;
 
-out:
-	close(fd);
 	return ret;
 }
 
-- 
2.16.1