Re: [PATCHv3 bpf-next] samples/bpf: add xdp program on egress for xdp_redirect_map

On Tue,  8 Dec 2020 16:18:56 +0800
Hangbin Liu [off-list ref] wrote:

This patch add a xdp program on egress to show that we can modify
the packet on egress. In this sample we will set the pkt's src
mac to egress's mac address. The xdp_prog will be attached when
-X option supplied.

Signed-off-by: Hangbin Liu <redacted>
---
v3:
a) modify the src mac address based on egress mac

v2:
a) use pkt counter instead of IP ttl modification on egress program
b) make the egress program selectable by option -X
---
 samples/bpf/xdp_redirect_map_kern.c |  60 ++++++++++-
 samples/bpf/xdp_redirect_map_user.c | 153 ++++++++++++++++++++--------
 2 files changed, 168 insertions(+), 45 deletions(-)

[...]

I would have expected (like ethtool):
 fd = socket(AF_INET, SOCK_DGRAM, 0);

+	if (fd < 0)
+		return -1;
+
+	if (!if_indextoname(ifindex_out, ifname))
+		return -1;
+
+	strcpy(ifr.ifr_name, ifname);
+
+	if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
+		return -1;
+
+	memcpy(mac_addr, ifr.ifr_hwaddr.sa_data, 6 * sizeof(char));
+	close(fd);
+
+	return 0;
+}

[...]

-	/* Loading dummy XDP prog on out-device */
-	if (bpf_set_link_xdp_fd(ifindex_out, dummy_prog_fd,
-			    (xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST)) < 0) {
-		printf("WARN: link set xdp fd failed on %d\n", ifindex_out);
-		ifindex_out_xdp_dummy_attached = false;
-	}
+	/* If -X supplied, load 2nd xdp prog on egress.
+	 * If not, just load dummy prog on egress.
+	 */

The dummy prog need to be loaded, regardless of 2nd xdp prog on egress.

+	if (xdp_devmap_attached) {
+		unsigned char mac_addr[6];
 
-	memset(&info, 0, sizeof(info));
-	ret = bpf_obj_get_info_by_fd(dummy_prog_fd, &info, &info_len);
-	if (ret) {
-		printf("can't get prog info - %s\n", strerror(errno));
-		return ret;
+		devmap_prog = bpf_object__find_program_by_title(obj, "xdp_devmap/map_prog");
+		if (!devmap_prog) {
+			printf("finding devmap_prog in obj file failed\n");
+			goto out;
+		}
+		devmap_prog_fd = bpf_program__fd(devmap_prog);
+		if (devmap_prog_fd < 0) {
+			printf("finding devmap_prog fd failed\n");
+			goto out;
+		}
+
+		if (get_mac_addr(ifindex_out, mac_addr) < 0) {
+			printf("get interface %d mac failed\n", ifindex_out);
+			goto out;
+		}
+
+		ret = bpf_map_update_elem(tx_mac_map_fd, &key, mac_addr, 0);
+		if (ret) {
+			perror("bpf_update_elem tx_mac_map_fd");
+			goto out;
+		}
+	} else if (ifindex_in != ifindex_out) {
+		dummy_prog = bpf_object__find_program_by_title(obj, "xdp_redirect_dummy");
+		if (!dummy_prog) {
+			printf("finding dummy_prog in obj file failed\n");
+			goto out;
+		}
+
+		dummy_prog_fd = bpf_program__fd(dummy_prog);
+		if (dummy_prog_fd < 0) {
+			printf("find dummy_prog fd failed\n");
+			goto out;
+		}
+
+		if (bpf_set_link_xdp_fd(ifindex_out, dummy_prog_fd,
+					(xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST)) == 0) {
+			ifindex_out_xdp_dummy_attached = true;
+		} else {
+			printf("WARN: link set xdp fd failed on %d\n", ifindex_out);
+		}
+
+		memset(&info, 0, sizeof(info));
+		ret = bpf_obj_get_info_by_fd(dummy_prog_fd, &info, &info_len);
+		if (ret) {
+			printf("can't get prog info - %s\n", strerror(errno));
+		}
+		dummy_prog_id = info.id;
 	}
-	dummy_prog_id = info.id;
 
 	signal(SIGINT, int_exit);
 	signal(SIGTERM, int_exit);
 
-	/* populate virtual to physical port map */
-	ret = bpf_map_update_elem(tx_port_map_fd, &key, &ifindex_out, 0);
+	devmap_val.ifindex = ifindex_out;
+	devmap_val.bpf_prog.fd = devmap_prog_fd;
+	ret = bpf_map_update_elem(tx_port_map_fd, &key, &devmap_val, 0);
 	if (ret) {
-		perror("bpf_update_elem");
+		perror("bpf_update_elem tx_port_map_fd");
 		goto out;
 	}
 
 	poll_stats(2, ifindex_out);
 
 out:
-	return 0;
+	bpf_object__close(obj);
+	return 1;
 }

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer