// SPDX-License-Identifier: GPL-2.0
/* Copyright Leon Hwang */

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>

#define ERRMSG_LEN 64

struct xdp_errmsg {
        char msg[ERRMSG_LEN];
};

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

struct xdp_attach_error_ctx {
        unsigned long unused;

        /*
         * bpf does not support tracepoint __data_loc directly.
         *
         * Actually, this field is a 32 bit integer whose value encodes
         * information on where to find the actual data. The first 2 bytes is
         * the size of the data. The last 2 bytes is the offset from the start
         * of the tracepoint struct where the data begins.
         * -- https://github.com/iovisor/bpftrace/pull/1542
         */
        __u32 msg; // __data_loc char[] msg;
};

/*
 * Catch the error message at the tracepoint.
 */

SEC("tp/xdp/bpf_xdp_link_attach_failed")
int tp__xdp__bpf_xdp_link_attach_failed(struct xdp_attach_error_ctx *ctx)
{
        char *msg = (void *)(__u64) ((void *) ctx + (__u16) ctx->msg);
        struct xdp_errmsg errmsg = {};

        bpf_probe_read_kernel_str(&errmsg.msg, ERRMSG_LEN, msg);
        bpf_perf_event_output(ctx, &xdp_errmsg_pb, BPF_F_CURRENT_CPU, &errmsg,
                              ERRMSG_LEN);
        return 0;
}

/*
 * Reuse the XDP program in xdp_dummy.c.
 */

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