| libtracefs(3) |
| ============= |
| |
| 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 |
| -------- |
| [verse] |
| -- |
| *#include <tracefs.h>* |
| |
| ssize_t *tracefs_trace_pipe_stream*(int _fd_, struct tracefs_instance pass:[*]_instance_, int _flags_); |
| ssize_t *tracefs_trace_pipe_print*(struct tracefs_instance pass:[*]_instance_, int _flags_); |
| void *tracefs_trace_pipe_stop*(struct tracefs_instance pass:[*]_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 ). 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. |
| |
| 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 |
| ------- |
| [source,c] |
| -- |
| #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 |
| ----- |
| [verse] |
| -- |
| *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 |
| ------ |
| [verse] |
| -- |
| *Steven Rostedt* <rostedt@goodmis.org> |
| *Tzvetomir Stoyanov* <tz.stoyanov@gmail.com> |
| -- |
| REPORTING BUGS |
| -------------- |
| Report bugs to <linux-trace-devel@vger.kernel.org> |
| |
| 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). |
