tracefs_trace_pipe_stream(3) — Linux manual page


LIBTRACEFS(3)               libtracefs Manual              LIBTRACEFS(3)

NAME         top

       tracefs_trace_pipe_stream, tracefs_trace_pipe_print,
       tracefs_trace_pipe_stop - redirect the stream of trace data to an
       output or stdout.

SYNOPSIS         top

       #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         top

       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)). 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         top

       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         top

           #include <stdio.h>
           #include <stdlib.h>
           #include <unistd.h>
           #include <signal.h>
           #include <fcntl.h>

           #include <tracefs.h>

           void stop(int sig)

           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]);
                   filename = argv[1];
                   fd = creat(filename, mode);
                   if (fd < 0) {
                   signal(SIGINT, stop);
                   ret = tracefs_trace_pipe_stream(fd, NULL, SPLICE_F_NONBLOCK);

                   return ret;

FILES         top

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

SEE ALSO         top

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

AUTHOR         top

           Steven Rostedt <[1]>
           Tzvetomir Stoyanov <[2]>

REPORTING BUGS         top

       Report bugs to <[3]>

LICENSE         top

       libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES         top 

COPYING         top

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

NOTES         top




COLOPHON         top

       This page is part of the libtracefs (Linux kernel trace file
       system library) project.  Information about the project can be
       found at ⟨⟩.  If you have a bug report
       for this manual page, see ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-07-05.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

libtracefs 1.7.0               12/22/2023                  LIBTRACEFS(3)