Helper function `bpf_xdp_output`

v5.7

This helper writes a raw data blob into a special BPF perf event held by map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.

Definition

Copyright (c) 2015 The Libbpf Authors. All rights reserved.

Returns 0 on success, or a negative error in case of failure.

static long (* const bpf_xdp_output)(void *ctx, void *map, __u64 flags, void *data, __u64 size) = (void *) 121;

Usage

The perf event must have the following attributes: PERF_SAMPLE_RAW as sample_type, PERF_TYPE_SOFTWARE as type, and PERF_COUNT_SW_BPF_OUTPUT as config.

The flags are used to indicate the index in map for which the value must be put, masked with BPF_F_INDEX_MASK. Alternatively, flags can be set to BPF_F_CURRENT_CPU to indicate that the index of the current CPU core should be used.

The value to write, of size, is passed through eBPF stack and pointed by data.

ctx is a pointer to in-kernel struct xdp_buff.

This helper is similar to bpf_perf_event_output but restricted to raw_tracepoint bpf programs.

Program types

This helper call can be used in the following program types:

BPF_PROG_TYPE_PERF_EVENT

Map types

This helper call can be used with the following map types:

BPF_MAP_TYPE_PERF_EVENT_ARRAY

Example

// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>

char _license[] SEC("license") = "GPL";

struct net_device {
    /* Structure does not need to contain all entries,
     * as "preserve_access_index" will use BTF to fix this...
     */
    int ifindex;
} __attribute__((preserve_access_index));

struct xdp_rxq_info {
    /* Structure does not need to contain all entries,
     * as "preserve_access_index" will use BTF to fix this...
     */
    struct net_device *dev;
    __u32 queue_index;
} __attribute__((preserve_access_index));

struct xdp_buff {
    void *data;
    void *data_end;
    void *data_meta;
    void *data_hard_start;
    unsigned long handle;
    struct xdp_rxq_info *rxq;
} __attribute__((preserve_access_index));

struct meta {
    int ifindex;
    int pkt_len;
};

struct {
    __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
    __type(key, int);
    __type(value, int);
} perf_buf_map SEC(".maps");

__u64 test_result_fentry = 0;
SEC("fentry/FUNC")
int BPF_PROG(trace_on_entry, struct xdp_buff *xdp)
{
    struct meta meta;

    meta.ifindex = xdp->rxq->dev->ifindex;
    meta.pkt_len = bpf_xdp_get_buff_len((struct xdp_md *)xdp);
    bpf_xdp_output(xdp, &perf_buf_map,
               ((__u64) meta.pkt_len << 32) |
               BPF_F_CURRENT_CPU,
               &meta, sizeof(meta));

    test_result_fentry = xdp->rxq->dev->ifindex;
    return 0;
}

__u64 test_result_fexit = 0;
SEC("fexit/FUNC")
int BPF_PROG(trace_on_exit, struct xdp_buff *xdp, int ret)
{
    test_result_fexit = ret;
    return 0;
}

Helper function bpf_xdp_output