// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

#define CLOCK_MONOTONIC 1

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

struct elem {
        struct bpf_timer timer;
};

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, 1);
        __type(key, int);
        __type(value, struct elem);
} timer_map SEC(".maps");

volatile int in_timer_start;
volatile int tp_called;

static int timer_cb(void *map, int *key, struct elem *value)
{
        return 0;
}

SEC("tp_btf/hrtimer_cancel")
int BPF_PROG(tp_hrtimer_cancel, struct hrtimer *hrtimer)
{
        struct bpf_timer *timer;
        int key = 0;

        if (!in_timer_start)
                return 0;

        tp_called = 1;
        timer = bpf_map_lookup_elem(&timer_map, &key);

        /*
         * Call bpf_timer_start() from the tracepoint within hrtimer logic
         * on the same timer to make sure it doesn't deadlock.
         */
        bpf_timer_start(timer, 1000000000, 0);
        return 0;
}

SEC("syscall")
int start_timer(void *ctx)
{
        struct bpf_timer *timer;
        int key = 0;

        timer = bpf_map_lookup_elem(&timer_map, &key);
        /* claude may complain here that there is no NULL check. Ignoring it. */
        bpf_timer_init(timer, &timer_map, CLOCK_MONOTONIC);
        bpf_timer_set_callback(timer, timer_cb);

        /*
         * call hrtimer_start() twice, so that 2nd call does
         * remove_hrtimer() and trace_hrtimer_cancel() tracepoint.
         */
        in_timer_start = 1;
        bpf_timer_start(timer, 1000000000, 0);
        bpf_timer_start(timer, 1000000000, 0);
        in_timer_start = 0;
        return 0;
}