---
name: "tracefs_trace_pipe_stream"
section: "3"
platform: "linux"
package: "libtracefs"
version: "1.8.4-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/tracefs_trace_pipe_stream"
---

# tracefs\_trace\_pipe\_stream(3)

redirect the stream of trace data to an output or stdout.

## NAME

tracefs\_trace\_pipe\_stream, tracefs\_trace\_pipe\_print, tracefs\_trace\_pipe\_stop - redirect the stream of trace data to an output or stdout.

## SYNOPSIS

```
#include <tracefs.h>
ssize_t tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
ssize_t tracefs_trace_pipe_print(struct tracefs_instance *instance, int flags);
void tracefs_trace_pipe_stop(struct tracefs_instance *instance);
```

## DESCRIPTION

If NULL is passed as *instance*, the top trace instance is used.

The reading of the trace\_pipe file can be stopped by calling **tracefs\_trace\_pipe\_stop()** which could be placed in a signal handler in case the application wants to stop the reading, for example, with the user pressing Ctrl-C.

The **tracefs\_trace\_pipe\_stream()** function redirects the stream of trace data to an output file. The "splice" system call is used to moves the data without copying between kernel address space and user address space. The *fd* is the file descriptor of the output file and *flags* is a bit mask of flags to be passed to the open system call of the trace\_pipe file (see **[open(2)](/open/2.md)**). If flags contain O\_NONBLOCK, then that is also passed to the splice calls that may read the file to the output stream file descriptor. Note, O\_RDONLY is or’d to the *flags* and only O\_NONBLOCK is useful for this parameter.

The **tracefs\_trace\_pipe\_print()** function is similar to **tracefs\_trace\_pipe\_stream()**, but the stream of trace data is redirected to stdout.

## RETURN VALUE

The **tracefs\_trace\_pipe\_stream()**, and **tracefs\_trace\_pipe\_print()** functions return the number of bytes transfered if the operation is successful, or -1 in case of an error.

## EXAMPLE

```
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <tracefs.h>
void stop(int sig)
{
        tracefs_trace_pipe_stop(NULL);
}
int main(int argc, char **argv)
{
        mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
        const char *filename;
        int fd;
        int ret;
        if (argc < 2) {
                fprintf(stderr, "usage: %s output_file\n", argv[0]);
                exit(-1);
        }
        filename = argv[1];
        fd = creat(filename, mode);
        if (fd < 0) {
                perror(filename);
                exit(-1);
        }
        signal(SIGINT, stop);
        ret = tracefs_trace_pipe_stream(fd, NULL, SPLICE_F_NONBLOCK);
        close(fd);
        return ret;
}
```

## FILES

```
tracefs.h
        Header file to include in order to have access to the library APIs.
-ltracefs
        Linker switch to add when building a program that uses the library.
```

## SEE ALSO

[**libtracefs**(3)](/libtracefs/3.md), [**libtraceevent**(3)](/libtraceevent/3.md), [**trace-cmd**(1)](/trace-cmd/1.md), Documentation/trace/ftrace.rst from the Linux kernel tree

## AUTHOR

```
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
```

## REPORTING BUGS

Report bugs to \<**linux-trace-devel@vger.kernel.org**\[3\]\>

## LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

## RESOURCES

**https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/**

## COPYING

Copyright (C) 2021 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).

## NOTES

- 1\.

  rostedt@goodmis.org

  mailto:rostedt@goodmis.org

- 2\.

  tz.stoyanov@gmail.com

  mailto:tz.stoyanov@gmail.com

- 3\.

  linux-trace-devel@vger.kernel.org

  mailto:linux-trace-devel@vger.kernel.org