Re: [PATCH] samples: bpf: add max_pckt_size option at xdp_adjust_tail

[Maciej Fijalkowski <maciejromanfijalkowski@gmail.com>]

On Mon, 26 Aug 2019 18:57:22 +0900
"Daniel T. Lee" <danieltimlee@gmail.com> wrote:

> Currently, at xdp_adjust_tail_kern.c, MAX_PCKT_SIZE is limited
> to 600. To make this size flexible, a new map 'pcktsz' is added.
> 
> By updating new packet size to this map from the userland,
> xdp_adjust_tail_kern.o will use this value as a new max_pckt_size.
> 
> If no '-P <MAX_PCKT_SIZE>' option is used, the size of maximum packet
> will be 600 as a default.
> 
> Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> ---
>  samples/bpf/xdp_adjust_tail_kern.c | 23 +++++++++++++++++++----
>  samples/bpf/xdp_adjust_tail_user.c | 21 +++++++++++++++++++--
>  2 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
> index 411fdb21f8bc..4d53af370b68 100644
> --- a/samples/bpf/xdp_adjust_tail_kern.c
> +++ b/samples/bpf/xdp_adjust_tail_kern.c
> @@ -25,6 +25,13 @@
>  #define ICMP_TOOBIG_SIZE 98
>  #define ICMP_TOOBIG_PAYLOAD_SIZE 92
>  
> +struct bpf_map_def SEC("maps") pcktsz = {
> +	.type = BPF_MAP_TYPE_ARRAY,
> +	.key_size = sizeof(__u32),
> +	.value_size = sizeof(__u32),
> +	.max_entries = 1,
> +};
> +
>  struct bpf_map_def SEC("maps") icmpcnt = {
>  	.type = BPF_MAP_TYPE_ARRAY,
>  	.key_size = sizeof(__u32),
> @@ -64,7 +71,8 @@ static __always_inline void ipv4_csum(void *data_start, int data_size,
>  	*csum = csum_fold_helper(*csum);
>  }
>  
> -static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
> +static __always_inline int send_icmp4_too_big(struct xdp_md *xdp,
> +					      __u32 max_pckt_size)
>  {
>  	int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
>  
> @@ -92,7 +100,7 @@ static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
>  	orig_iph = data + off;
>  	icmp_hdr->type = ICMP_DEST_UNREACH;
>  	icmp_hdr->code = ICMP_FRAG_NEEDED;
> -	icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));
> +	icmp_hdr->un.frag.mtu = htons(max_pckt_size - sizeof(struct ethhdr));
>  	icmp_hdr->checksum = 0;
>  	ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
>  	icmp_hdr->checksum = csum;
> @@ -118,14 +126,21 @@ static __always_inline int handle_ipv4(struct xdp_md *xdp)
>  {
>  	void *data_end = (void *)(long)xdp->data_end;
>  	void *data = (void *)(long)xdp->data;
> +	__u32 max_pckt_size = MAX_PCKT_SIZE;
> +	__u32 *pckt_sz;
> +	__u32 key = 0;
>  	int pckt_size = data_end - data;
>  	int offset;
>  
> -	if (pckt_size > MAX_PCKT_SIZE) {
> +	pckt_sz = bpf_map_lookup_elem(&pcktsz, &key);
> +	if (pckt_sz && *pckt_sz)
> +		max_pckt_size = *pckt_sz;
> +
> +	if (pckt_size > max_pckt_size) {
>  		offset = pckt_size - ICMP_TOOBIG_SIZE;
>  		if (bpf_xdp_adjust_tail(xdp, 0 - offset))
>  			return XDP_PASS;
> -		return send_icmp4_too_big(xdp);
> +		return send_icmp4_too_big(xdp, max_pckt_size);
>  	}
>  	return XDP_PASS;
>  }
> diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
> index a3596b617c4c..dd3befa5e1fe 100644
> --- a/samples/bpf/xdp_adjust_tail_user.c
> +++ b/samples/bpf/xdp_adjust_tail_user.c
> @@ -72,6 +72,7 @@ static void usage(const char *cmd)
>  	printf("Usage: %s [...]\n", cmd);
>  	printf("    -i <ifname|ifindex> Interface\n");
>  	printf("    -T <stop-after-X-seconds> Default: 0 (forever)\n");
> +	printf("    -P <MAX_PCKT_SIZE> Default: 600\n");
>  	printf("    -S use skb-mode\n");
>  	printf("    -N enforce native mode\n");
>  	printf("    -F force loading prog\n");
> @@ -85,9 +86,11 @@ int main(int argc, char **argv)
>  		.prog_type	= BPF_PROG_TYPE_XDP,
>  	};
>  	unsigned char opt_flags[256] = {};
> -	const char *optstr = "i:T:SNFh";
> +	const char *optstr = "i:T:P:SNFh";
>  	struct bpf_prog_info info = {};
>  	__u32 info_len = sizeof(info);
> +	__u32 max_pckt_size = 0;
> +	__u32 key = 0;
>  	unsigned int kill_after_s = 0;
>  	int i, prog_fd, map_fd, opt;
>  	struct bpf_object *obj;
> @@ -110,6 +113,9 @@ int main(int argc, char **argv)
>  		case 'T':
>  			kill_after_s = atoi(optarg);
>  			break;
> +		case 'P':
> +			max_pckt_size = atoi(optarg);
> +			break;
>  		case 'S':
>  			xdp_flags |= XDP_FLAGS_SKB_MODE;
>  			break;
> @@ -150,9 +156,20 @@ int main(int argc, char **argv)
>  	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
>  		return 1;
>  
> +	/* update pcktsz map */
>  	map = bpf_map__next(NULL, obj);
>  	if (!map) {
> -		printf("finding a map in obj file failed\n");
> +		printf("finding a pcktsz map in obj file failed\n");
> +		return 1;
> +	}
> +	map_fd = bpf_map__fd(map);

Consider using bpf_object__find_map_fd_by_name() here.

> +	if (max_pckt_size)
> +		bpf_map_update_elem(map_fd, &key, &max_pckt_size, BPF_ANY);
> +
> +	/* fetch icmpcnt map */
> +	map = bpf_map__next(map, obj);
> +	if (!map) {
> +		printf("finding a icmpcnt map in obj file failed\n");
>  		return 1;
>  	}
>  	map_fd = bpf_map__fd(map);