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)). 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), libtraceevent(3), trace-cmd(1), 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