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// 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 <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <asm/bitsperlong.h>
#include <endian.h>
#include <linux/user_events.h>
#if __BITS_PER_LONG == 64
#define endian_swap(x) htole64(x)
#else
#define endian_swap(x) htole32(x)
#endif
/* Assumes debugfs is mounted */
const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
static int event_status(long **status)
{
int fd = open(status_file, O_RDONLY);
*status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
MAP_SHARED, fd, 0);
close(fd);
if (*status == MAP_FAILED)
return -1;
return 0;
}
static int event_reg(int fd, const char *command, long *index, long *mask,
int *write)
{
struct user_reg reg = {0};
reg.size = sizeof(reg);
reg.name_args = (__u64)command;
if (ioctl(fd, DIAG_IOCSREG, ®) == -1)
return -1;
*index = reg.status_bit / __BITS_PER_LONG;
*mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
*write = reg.write_index;
return 0;
}
int main(int argc, char **argv)
{
int data_fd, write;
long index, mask;
long *status_page;
struct iovec io[2];
__u32 count = 0;
if (event_status(&status_page) == -1)
return errno;
data_fd = open(data_file, O_RDWR);
if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -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 (status_page[index] & mask) {
/* 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;
}
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