Skip to content
tcpdump like XDP packet capture
Branch: master
Clone or download
arthurfabre Update cbpfc to latest, adapt filter generation
Update cbpfc to the latest release, which includes some breaking API
changes. Rework the eBPF filter generation to use the new single filter
return label, instead of the separate match / no match labels.
Latest commit a5b2182 Apr 26, 2019

README.md

xdpcap

xdpcap is a tcpdump like tool for eXpress Data Path (XDP). It can capture packets and actions / return codes from XDP programs, using standard tcpdump / libpcap filter expressions.

Instrumentation

XDP programs need to expose at least one hook point:

struct bpf_map_def xdpcap_hook = {
	.type = BPF_MAP_TYPE_PROG_ARRAY,
	.key_size = sizeof(int),
	.value_size = sizeof(int),
	.max_entries = 4, // The max value of XDP_* constants
};

This map must be pinned inside a bpffs.

hook.h provides a convenience macro for declaring such maps:

#include "hook.h"

struct bpf_map_def xdpcap_hook = XDPCAP_HOOK();

return XDP_* statements should be modified to "feed" a hook:

#include "hook.h"

struct bpf_map_def xdpcap_hook = XDPCAP_HOOK();

int xdp_main(struct xdp_md *ctx) {
	return xdpcap_exit(ctx, &xdpcap_hook, XDP_PASS);
}

For a full example, see testdata/xdp_hook.c.

Depending on the granularity desired, a program can expose multiple hook points, or a hook can be reused across programs by using the same underlying map.

Package xdpcap provides a wrapper for creating and pinning the hook maps using the newtools/ebpf loader.

Installation

go get -u github.com/cloudflare/xdpcap/cmd/xdpcap

Usage

  • Capture packets to a pcap: xdpcap /path/to/pinned/map dump.pcap "tcp and port 80"

  • Display captured packets: sudo xdpcap /path/to/pinned/map - "tcp and port 80" | sudo tcpdump -r -

Limitations

  • filters run after the instrumented XDP program. If the program modifies the packet, the filter should match the modified packet, not the original input packet.

Tests

  • sudo -E $(which go) test
You can’t perform that action at this time.