// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2021, Microsoft Corporation.
 *
 * Authors:
 *   Beau Belgrave <beaub@linux.microsoft.com>
 */

#include <errno.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/user_events.h>

const char *data_file = "/sys/kernel/tracing/user_events_data";
int enabled = 0;

static int event_reg(int fd, const char *command, int *write, int *enabled)
{
        struct user_reg reg = {0};

        reg.size = sizeof(reg);
        reg.enable_bit = 31;
        reg.enable_size = sizeof(*enabled);
        reg.enable_addr = (__u64)enabled;
        reg.name_args = (__u64)command;

        if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
                return -1;

        *write = reg.write_index;

        return 0;
}

int main(int argc, char **argv)
{
        int data_fd, write;
        struct iovec io[2];
        __u32 count = 0;

        data_fd = open(data_file, O_RDWR);

        if (event_reg(data_fd, "test u32 count", &write, &enabled) == -1)
                return errno;

        /* Setup iovec */
        io[0].iov_base = &write;
        io[0].iov_len = sizeof(write);
        io[1].iov_base = &count;
        io[1].iov_len = sizeof(count);
ask:
        printf("Press enter to check status...\n");
        getchar();

        /* Check if anyone is listening */
        if (enabled) {
                /* Yep, trace out our data */
                writev(data_fd, (const struct iovec *)io, 2);

                /* Increase the count */
                count++;

                printf("Something was attached, wrote data\n");
        }

        goto ask;

        return 0;
}