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samples: bpf: Add max_pckt_size option at xdp_adjust_tail

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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.

For clarity, change the helper to fetch map from 'bpf_map__next'
to 'bpf_object__find_map_fd_by_name'. Also, 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@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191007172117.3916-1-danieltimlee@gmail.com
This commit is contained in:
Daniel T. Lee 2019-10-08 02:21:17 +09:00 committed by Alexei Starovoitov
parent 72ccd9200f
commit 8fdf5b780a
2 changed files with 25 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
samples/bpf/xdp_adjust_tail_kern.c
View File

@ -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;

29
samples/bpf/xdp_adjust_tail_user.c
View File

@ -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 +156,20 @@ 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");
return 1;
/* 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);
}
map_fd = bpf_map__fd(map);
if (!prog_fd) {
printf("load_bpf_file: %s\n", strerror(errno));
/* 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;
}