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Date: Sun, 6 Oct 2019 20:37:34 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: "Daniel T. Lee" <danieltimlee@...il.com>
Cc: Yonghong Song <yhs@...com>, Song Liu <liu.song.a23@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>
Subject: Re: [bpf-next v5] samples: bpf: add max_pckt_size option at xdp_adjust_tail
On Sun, Oct 6, 2019 at 4:58 AM Daniel T. Lee <danieltimlee@...il.com> wrote:
>
> Currently, at xdp_adjust_tail_kern.c, MAX_PCKT_SIZE is limited
> to 600. To make this size flexible, static global variable
> 'max_pcktsz' is added.
>
> By updating new packet size from the user space, xdp_adjust_tail_kern.o
> will use this value as a new max packet size.
>
> This static global variable can be accesible from .data section with
> bpf_object__find_map* from user space, since it is considered as
> internal map (accessible with .bss/.data/.rodata suffix).
>
> If no '-P <MAX_PCKT_SIZE>' option is used, the size of maximum packet
> will be 600 as a default.
>
> Changed the way to test prog_fd, map_fd from '!= 0' to '< 0',
> since fd could be 0 when stdin is closed.
>
> Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
>
> ---
See nit below, but otherwise looks good.
Acked-by: Andrii Nakryiko <andriin@...com>
> Changes in v5:
> - Change pcktsz map to static global variable
> Changes in v4:
> - make pckt_size no less than ICMP_TOOBIG_SIZE
> - Fix code style
> Changes in v2:
> - Change the helper to fetch map from 'bpf_map__next' to
> 'bpf_object__find_map_fd_by_name'.
>
> samples/bpf/xdp_adjust_tail_kern.c | 7 +++++--
> samples/bpf/xdp_adjust_tail_user.c | 32 ++++++++++++++++++++++--------
> 2 files changed, 29 insertions(+), 10 deletions(-)
>
> diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
> index 411fdb21f8bc..c616508befb9 100644
> --- a/samples/bpf/xdp_adjust_tail_kern.c
> +++ b/samples/bpf/xdp_adjust_tail_kern.c
> @@ -25,6 +25,9 @@
> #define ICMP_TOOBIG_SIZE 98
> #define ICMP_TOOBIG_PAYLOAD_SIZE 92
>
> +/* volatile to prevent compiler optimizations */
> +static volatile __u32 max_pcktsz = MAX_PCKT_SIZE;
> +
> struct bpf_map_def SEC("maps") icmpcnt = {
> .type = BPF_MAP_TYPE_ARRAY,
> .key_size = sizeof(__u32),
> @@ -92,7 +95,7 @@ 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_pcktsz - sizeof(struct ethhdr));
> icmp_hdr->checksum = 0;
> ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
> icmp_hdr->checksum = csum;
> @@ -121,7 +124,7 @@ static __always_inline int handle_ipv4(struct xdp_md *xdp)
> int pckt_size = data_end - data;
> int offset;
>
> - if (pckt_size > MAX_PCKT_SIZE) {
> + if (pckt_size > max(max_pcktsz, ICMP_TOOBIG_SIZE)) {
> offset = pckt_size - ICMP_TOOBIG_SIZE;
> if (bpf_xdp_adjust_tail(xdp, 0 - offset))
> return XDP_PASS;
> diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
> index a3596b617c4c..bcdebd3be83e 100644
> --- a/samples/bpf/xdp_adjust_tail_user.c
> +++ b/samples/bpf/xdp_adjust_tail_user.c
> @@ -23,6 +23,7 @@
> #include "libbpf.h"
>
> #define STATS_INTERVAL_S 2U
> +#define MAX_PCKT_SIZE 600
>
> static int ifindex = -1;
> static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
> @@ -72,6 +73,7 @@ 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: %u\n", MAX_PCKT_SIZE);
> printf(" -S use skb-mode\n");
> printf(" -N enforce native mode\n");
> printf(" -F force loading prog\n");
> @@ -85,13 +87,14 @@ 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);
> unsigned int kill_after_s = 0;
> int i, prog_fd, map_fd, opt;
> struct bpf_object *obj;
> - struct bpf_map *map;
> + __u32 max_pckt_size = 0;
> + __u32 key = 0;
> char filename[256];
> int err;
>
> @@ -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;
> @@ -150,15 +156,25 @@ int main(int argc, char **argv)
> if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
> return 1;
>
> - map = bpf_map__next(NULL, obj);
> - if (!map) {
> - printf("finding a map in obj file failed\n");
> + if (prog_fd < 0) {
> + printf("load_bpf_file: %s\n", strerror(errno));
program load error is checked above (bpf_prog_load_xattr check), not
clear why check this again... Maybe just print helpful message there?
> return 1;
> }
> - map_fd = bpf_map__fd(map);
>
> - if (!prog_fd) {
> - printf("load_bpf_file: %s\n", strerror(errno));
> + /* static global var 'max_pcktsz' is accessible from .data section */
> + if (max_pckt_size) {
> + map_fd = bpf_object__find_map_fd_by_name(obj, "xdp_adju.data");
> + if (map_fd < 0) {
> + printf("finding a max_pcktsz map in obj file failed\n");
> + return 1;
> + }
> + bpf_map_update_elem(map_fd, &key, &max_pckt_size, BPF_ANY);
> + }
> +
> + /* fetch icmpcnt map */
> + map_fd = bpf_object__find_map_fd_by_name(obj, "icmpcnt");
> + if (map_fd < 0) {
> + printf("finding a icmpcnt map in obj file failed\n");
> return 1;
> }
>
> --
> 2.20.1
>
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