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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
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7
samples/bpf/xdp_adjust_tail_kern.c
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@@ -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;