samples: bpf: Add max_pckt_size option at xdp_adjust_tail

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

diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
index 411fdb21f8bcf62efac06bdf8a80997e3615c7f5..c616508befb98ba83ae2e9cc6b3063e1c5f2f7bf 100644 (file)
--- 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 a3596b617c4ce836f8908efa4d3ad54d66093db9..d86e9ad0356bd60131ab49359968412d603a5a25 100644 (file)
--- 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 +156,20 @@ 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;
        }