Subject: Re: [PATCHv8 bpf-next] samples/bpf: add xdp program on egress for xdp_redirect_map

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 19 Jan 2021 15:51:27 +0100

On Tue, 19 Jan 2021 11:12:07 +0800
Hangbin Liu <[email-masked]> 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.
> 
> Acked-by: Yonghong Song <[email-masked]>
> Signed-off-by: Hangbin Liu <[email-masked]>
> 
> ---
> v8: Fix some checkpatch issues.
> 
> v7:
> a) use bpf_object__find_program_by_name() instad of
>    bpf_object__find_program_by_title()
> b) set default devmap fd to 0
> 
> v6: no code update, only rebase the code on latest bpf-next
> 
> v5:
> a) close fd when err out in get_mac_addr()
> b) exit program when both -S and -X supplied.
> 
> v4:
> a) Update get_mac_addr socket create
> b) Load dummy prog regardless of 2nd xdp prog on egress
> 
> 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 |  79 ++++++++++++++--
>  samples/bpf/xdp_redirect_map_user.c | 140 ++++++++++++++++++++++++----
>  2 files changed, 193 insertions(+), 26 deletions(-)
> 
> diff --git a/samples/bpf/xdp_redirect_map_kern.c b/samples/bpf/xdp_redirect_map_kern.c
> index 6489352ab7a4..e5c0d07a82d8 100644
> --- a/samples/bpf/xdp_redirect_map_kern.c
> +++ b/samples/bpf/xdp_redirect_map_kern.c
> @@ -19,12 +19,22 @@
>  #include <linux/ipv6.h>
>  #include <bpf/bpf_helpers.h>
>  
> +/* The 2nd xdp prog on egress does not support skb mode, so we define two
> + * maps, tx_port_general and tx_port_native.
> + */
>  struct {
>  	__uint(type, BPF_MAP_TYPE_DEVMAP);
>  	__uint(key_size, sizeof(int));
>  	__uint(value_size, sizeof(int));
>  	__uint(max_entries, 100);
> -} tx_port SEC(".maps");
> +} tx_port_general SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_DEVMAP);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(struct bpf_devmap_val));
> +	__uint(max_entries, 100);
> +} tx_port_native SEC(".maps");
>  
>  /* Count RX packets, as XDP bpf_prog doesn't get direct TX-success
>   * feedback.  Redirect TX errors can be caught via a tracepoint.
> @@ -36,6 +46,14 @@ struct {
>  	__uint(max_entries, 1);
>  } rxcnt SEC(".maps");
>  
> +/* map to store egress interface mac address */
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__type(key, u32);
> +	__type(value, __be64);
> +	__uint(max_entries, 1);
> +} tx_mac SEC(".maps");
> +
>  static void swap_src_dst_mac(void *data)
>  {
>  	unsigned short *p = data;
> @@ -52,17 +70,16 @@ static void swap_src_dst_mac(void *data)
>  	p[5] = dst[2];
>  }
>  
> -SEC("xdp_redirect_map")
> -int xdp_redirect_map_prog(struct xdp_md *ctx)
> +static int xdp_redirect_map(struct xdp_md *ctx, void *redirect_map)
>  {
>  	void *data_end = (void *)(long)ctx->data_end;
>  	void *data = (void *)(long)ctx->data;
>  	struct ethhdr *eth = data;
>  	int rc = XDP_DROP;
> -	int vport, port = 0, m = 0;
>  	long *value;
>  	u32 key = 0;
>  	u64 nh_off;
> +	int vport;
>  
>  	nh_off = sizeof(*eth);
>  	if (data + nh_off > data_end)
> @@ -73,13 +90,63 @@ int xdp_redirect_map_prog(struct xdp_md *ctx)
>  
>  	/* count packet in global counter */
>  	value = bpf_map_lookup_elem(&rxcnt, &key);
> -	if (value)
> +	if (value) {
>  		*value += 1;
> +		if (*value % 2 == 1)
> +			vport = 1;

This will also change the base behavior of the program, e.g when we are
not testing the 2nd xdp-prog.  It will become hard to compare the
performance between xdp_redirect and xdp_redirect_map.

It looks like you are populating vport=0 and vport=1 with the same ifindex.
Thus, this code is basically doing packet reordering, due to the per
CPU bulking layer (of 16 packets) in devmap.
Is this the intended behavior?

> +	}
>  
>  	swap_src_dst_mac(data);
>  
>  	/* send packet out physical port */
> -	return bpf_redirect_map(&tx_port, vport, 0);
> +	return bpf_redirect_map(redirect_map, vport, 0);
> +}
> +
> +static int xdp_redirect_map_egress(struct xdp_md *ctx, unsigned char *mac)
> +{
> +	void *data_end = (void *)(long)ctx->data_end;
> +	void *data = (void *)(long)ctx->data;
> +	struct ethhdr *eth = data;
> +	u32 key = 0;
> +	u64 nh_off;
> +
> +	nh_off = sizeof(*eth);
> +	if (data + nh_off > data_end)
> +		return XDP_DROP;
> +
> +	__builtin_memcpy(eth->h_source, mac, ETH_ALEN);
> +
> +	return XDP_PASS;
> +}
> +
> +SEC("xdp_redirect_general")
> +int xdp_redirect_map_general(struct xdp_md *ctx)
> +{
> +	return xdp_redirect_map(ctx, &tx_port_general);
> +}
> +
> +SEC("xdp_redirect_native")
> +int xdp_redirect_map_native(struct xdp_md *ctx)
> +{
> +	return xdp_redirect_map(ctx, &tx_port_native);
> +}
> +
> +/* This program will set src mac to 00:00:00:00:00:01 */
> +SEC("xdp_devmap/map_prog_0")
> +int xdp_redirect_map_egress_0(struct xdp_md *ctx)
> +{
> +	unsigned char mac[6] = {0x0, 0x0, 0x0, 0x0, 0x0, 0x1};
> +
> +	return xdp_redirect_map_egress(ctx, mac);
> +}
> +
> +/* This program will set src mac to 00:00:00:00:01:01 */
> +SEC("xdp_devmap/map_prog_1")
> +int xdp_redirect_map_egress_1(struct xdp_md *ctx)
> +{
> +	unsigned char mac[6] = {0x0, 0x0, 0x0, 0x0, 0x1, 0x1};
> +
> +	return xdp_redirect_map_egress(ctx, mac);
>  }
>  
>  /* Redirect require an XDP bpf_prog loaded on the TX device */
> diff --git a/samples/bpf/xdp_redirect_map_user.c b/samples/bpf/xdp_redirect_map_user.c
> index 31131b6e7782..99c3bdea3e49 100644
> --- a/samples/bpf/xdp_redirect_map_user.c
> +++ b/samples/bpf/xdp_redirect_map_user.c
> @@ -14,6 +14,10 @@
>  #include <unistd.h>
>  #include <libgen.h>
>  #include <sys/resource.h>
> +#include <sys/ioctl.h>
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <netinet/in.h>
>  
>  #include "bpf_util.h"
>  #include <bpf/bpf.h>
> @@ -22,6 +26,7 @@
>  static int ifindex_in;
>  static int ifindex_out;
>  static bool ifindex_out_xdp_dummy_attached = true;
> +static bool xdp_devmap_attached;
>  static __u32 prog_id;
>  static __u32 dummy_prog_id;
>  
> @@ -83,6 +88,32 @@ static void poll_stats(int interval, int ifindex)
>  	}
>  }
>  
> +static int get_mac_addr(unsigned int ifindex_out, void *mac_addr)
> +{
> +	char ifname[IF_NAMESIZE];
> +	struct ifreq ifr;
> +	int fd, ret = -1;
> +
> +	fd = socket(AF_INET, SOCK_DGRAM, 0);
> +	if (fd < 0)
> +		return ret;
> +
> +	if (!if_indextoname(ifindex_out, ifname))
> +		goto err_out;
> +
> +	strcpy(ifr.ifr_name, ifname);
> +
> +	if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
> +		goto err_out;
> +
> +	memcpy(mac_addr, ifr.ifr_hwaddr.sa_data, 6 * sizeof(char));
> +	ret = 0;
> +
> +err_out:
> +	close(fd);
> +	return ret;
> +}
> +
>  static void usage(const char *prog)
>  {
>  	fprintf(stderr,
> @@ -90,24 +121,27 @@ static void usage(const char *prog)
>  		"OPTS:\n"
>  		"    -S    use skb-mode\n"
>  		"    -N    enforce native mode\n"
> -		"    -F    force loading prog\n",
> +		"    -F    force loading prog\n"
> +		"    -X    load xdp program on egress\n",
>  		prog);
>  }
>  
>  int main(int argc, char **argv)
>  {
>  	struct bpf_prog_load_attr prog_load_attr = {
> -		.prog_type	= BPF_PROG_TYPE_XDP,
> +		.prog_type	= BPF_PROG_TYPE_UNSPEC,
>  	};
> -	struct bpf_program *prog, *dummy_prog;
> +	struct bpf_program *prog, *dummy_prog, *devmap_prog;
> +	int devmap_prog_fd_0 = 0, devmap_prog_fd_1 = 0;
> +	int prog_fd, dummy_prog_fd;
> +	int tx_port_map_fd, tx_mac_map_fd;
> +	struct bpf_devmap_val devmap_val;
>  	struct bpf_prog_info info = {};
>  	__u32 info_len = sizeof(info);
> -	int prog_fd, dummy_prog_fd;
> -	const char *optstr = "FSN";
> +	const char *optstr = "FSNX";
>  	struct bpf_object *obj;
>  	int ret, opt, key = 0;
>  	char filename[256];
> -	int tx_port_map_fd;
>  
>  	while ((opt = getopt(argc, argv, optstr)) != -1) {
>  		switch (opt) {
> @@ -120,14 +154,21 @@ int main(int argc, char **argv)
>  		case 'F':
>  			xdp_flags &= ~XDP_FLAGS_UPDATE_IF_NOEXIST;
>  			break;
> +		case 'X':
> +			xdp_devmap_attached = true;
> +			break;
>  		default:
>  			usage(basename(argv[0]));
>  			return 1;
>  		}
>  	}
>  
> -	if (!(xdp_flags & XDP_FLAGS_SKB_MODE))
> +	if (!(xdp_flags & XDP_FLAGS_SKB_MODE)) {
>  		xdp_flags |= XDP_FLAGS_DRV_MODE;
> +	} else if (xdp_devmap_attached) {
> +		printf("Load xdp program on egress with SKB mode not supported yet\n");
> +		return 1;
> +	}
>  
>  	if (optind == argc) {
>  		printf("usage: %s <IFNAME|IFINDEX>_IN <IFNAME|IFINDEX>_OUT\n", argv[0]);
> @@ -150,24 +191,28 @@ int main(int argc, char **argv)
>  	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
>  		return 1;
>  
> -	prog = bpf_program__next(NULL, obj);
> -	dummy_prog = bpf_program__next(prog, obj);
> -	if (!prog || !dummy_prog) {
> -		printf("finding a prog in obj file failed\n");
> -		return 1;
> +	if (xdp_flags & XDP_FLAGS_SKB_MODE) {
> +		prog = bpf_object__find_program_by_name(obj, "xdp_redirect_map_general");
> +		tx_port_map_fd = bpf_object__find_map_fd_by_name(obj, "tx_port_general");
> +	} else {
> +		prog = bpf_object__find_program_by_name(obj, "xdp_redirect_map_native");
> +		tx_port_map_fd = bpf_object__find_map_fd_by_name(obj, "tx_port_native");
>  	}
> -	/* bpf_prog_load_xattr gives us the pointer to first prog's fd,
> -	 * so we're missing only the fd for dummy prog
> -	 */
> +	dummy_prog = bpf_object__find_program_by_name(obj, "xdp_redirect_dummy_prog");
> +	if (!prog || dummy_prog < 0 || tx_port_map_fd < 0) {
> +		printf("finding prog/dummy_prog/tx_port_map in obj file failed\n");
> +		goto out;
> +	}
> +	prog_fd = bpf_program__fd(prog);
>  	dummy_prog_fd = bpf_program__fd(dummy_prog);
> -	if (prog_fd < 0 || dummy_prog_fd < 0) {
> +	if (prog_fd < 0 || dummy_prog_fd < 0 || tx_port_map_fd < 0) {
>  		printf("bpf_prog_load_xattr: %s\n", strerror(errno));
>  		return 1;
>  	}
>  
> -	tx_port_map_fd = bpf_object__find_map_fd_by_name(obj, "tx_port");
> +	tx_mac_map_fd = bpf_object__find_map_fd_by_name(obj, "tx_mac");
>  	rxcnt_map_fd = bpf_object__find_map_fd_by_name(obj, "rxcnt");
> -	if (tx_port_map_fd < 0 || rxcnt_map_fd < 0) {
> +	if (tx_mac_map_fd < 0 || rxcnt_map_fd < 0) {
>  		printf("bpf_object__find_map_fd_by_name failed\n");
>  		return 1;
>  	}
> @@ -199,11 +244,66 @@ int main(int argc, char **argv)
>  	}
>  	dummy_prog_id = info.id;
>  
> +	/* Load 2nd xdp prog on egress. */
> +	if (xdp_devmap_attached) {
> +		unsigned char mac_addr[6];
> +
> +		devmap_prog = bpf_object__find_program_by_name(obj, "xdp_redirect_map_egress_0");
> +		if (!devmap_prog) {
> +			printf("finding devmap_prog in obj file failed\n");
> +			goto out;
> +		}
> +		devmap_prog_fd_0 = bpf_program__fd(devmap_prog);
> +		if (devmap_prog_fd_0 < 0) {
> +			printf("finding devmap_prog fd failed\n");
> +			goto out;
> +		}
> +
> +		devmap_prog = bpf_object__find_program_by_name(obj, "xdp_redirect_map_egress_1");
> +		if (!devmap_prog) {
> +			printf("finding devmap_prog in obj file failed\n");
> +			goto out;
> +		}
> +		devmap_prog_fd_1 = bpf_program__fd(devmap_prog);
> +		if (devmap_prog_fd_1 < 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;
> +		}
> +	}
> +
>  	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 prog 0 will set src mac to 00:00:00:00:00:01
> +	 * if 2nd xdp prog attached on egress
> +	 */
> +	key = 0;
> +	devmap_val.ifindex = ifindex_out;

(ifindex_out same as below)

> +	devmap_val.bpf_prog.fd = devmap_prog_fd_0;
> +	ret = bpf_map_update_elem(tx_port_map_fd, &key, &devmap_val, 0);
> +	if (ret) {
> +		perror("bpf_update_elem");
> +		goto out;
> +	}
> +
> +	/* devmap prog 1 will set src mac to 00:00:00:00:01:01
> +	 * if 2nd xdp prog attached on egress
> +	 */
> +	key = 1;
> +	devmap_val.ifindex = ifindex_out;

(ifindex_out same as above)

> +	devmap_val.bpf_prog.fd = devmap_prog_fd_1;
> +	ret = bpf_map_update_elem(tx_port_map_fd, &key, &devmap_val, 0);
>  	if (ret) {
>  		perror("bpf_update_elem");
>  		goto out;

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