Tutorial: Tracing02 - monitor xdp raw tracepoints

In this lesson we will show how to attach to and monitor all xdp related raw tracepoints and some related info to user space stat application.

Table of Contents

• RAW tracepoints
• Assignments
  • Assignment 1: Monitor all xdp tracepoints

RAW tracepoints

The RAW tracepoint is eBPF alternative to standard tracepoint, which allows attaching eBPF program to tracepoint without the perf layer being involved/executed.

The bpf library expects the raw tracepoint eBPF program to be stored in a section with following name:

raw_tracepoint/<sys>/<tracepoint>

where <sys> is the tracepoint subsystem and <tracepoint> is the tracepoint name, which can be done with following construct:

SEC("raw_tracepoint/xdp/xdp_exception")
int trace_xdp_exception(struct xdp_exception_ctx *ctx)

The libbpf library exports interface to load and attach raw tracepoint programs, following call will load every program in the cfg->filename object as raw tracepoint programs:

err = bpf_prog_load(cfg->filename, BPF_PROG_TYPE_RAW_TRACEPOINT, &obj, &bpf_fd));

You can then iterate through all the programs and attach every program to the raw tracepoint:

bpf_object__for_each_program(prog, obj) {
	...
	bpf_fd = bpf_program__fd(prog);
	...
	err = bpf_raw_tracepoint_open(tp, bpf_fd);
	...
}

for more details please check load_bpf_and_trace_attach function in trace_load_and_stats.c object.

Assignments

Assignment 1: Monitor all xdp tracepoints

$ sudo ./trace_load_and_stats
XDP-event       CPU:to  pps          drop-pps     extra-info
XDP_REDIRECT    total   0            0            Success
XDP_REDIRECT    total   0            0            Error
Exception       0       0            11           XDP_UNKNOWN
Exception       1       0            2            XDP_UNKNOWN
Exception       2       0            36           XDP_UNKNOWN
Exception       3       0            29           XDP_UNKNOWN
Exception       4       0            3            XDP_UNKNOWN
Exception       5       0            8            XDP_UNKNOWN
Exception       total   0            91           XDP_UNKNOWN
cpumap-kthread  total   0            0            0          
devmap-xmit     total   0            0            0.00