127 lines
3.1 KiB
Plaintext
127 lines
3.1 KiB
Plaintext
libtracefs(3)
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=============
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NAME
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----
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tracefs_trace_pipe_stream, tracefs_trace_pipe_print, tracefs_trace_pipe_stop -
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redirect the stream of trace data to an output or stdout.
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SYNOPSIS
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--------
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[verse]
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--
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*#include <tracefs.h>*
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ssize_t *tracefs_trace_pipe_stream*(int _fd_, struct tracefs_instance pass:[*]_instance_, int _flags_);
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ssize_t *tracefs_trace_pipe_print*(struct tracefs_instance pass:[*]_instance_, int _flags_);
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void *tracefs_trace_pipe_stop*(struct tracefs_instance pass:[*]_instance_);
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--
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DESCRIPTION
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-----------
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If NULL is passed as _instance_, the top trace instance is used.
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The reading of the trace_pipe file can be stopped by calling *tracefs_trace_pipe_stop()*
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which could be placed in a signal handler in case the application wants to stop the
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reading, for example, with the user pressing Ctrl-C.
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The *tracefs_trace_pipe_stream()* function redirects the stream of trace data to an output
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file. The "splice" system call is used to moves the data without copying between kernel
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address space and user address space. The _fd_ is the file descriptor of the output file
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and _flags_ is a bit mask of flags to be passed to the open system call of the trace_pipe
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file (see ). If flags contain O_NONBLOCK, then that is also passed to the splice calls
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that may read the file to the output stream file descriptor.
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The *tracefs_trace_pipe_print()* function is similar to *tracefs_trace_pipe_stream()*, but
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the stream of trace data is redirected to stdout.
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RETURN VALUE
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------------
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The *tracefs_trace_pipe_stream()*, and *tracefs_trace_pipe_print()* functions return the
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number of bytes transfered if the operation is successful, or -1 in case of an error.
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EXAMPLE
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-------
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[source,c]
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--
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <signal.h>
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#include <fcntl.h>
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#include <tracefs.h>
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void stop(int sig)
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{
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tracefs_trace_pipe_stop(NULL);
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}
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int main(int argc, char **argv)
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{
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mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
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const char *filename;
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int fd;
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int ret;
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if (argc < 2) {
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fprintf(stderr, "usage: %s output_file\n", argv[0]);
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exit(-1);
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}
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filename = argv[1];
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fd = creat(filename, mode);
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if (fd < 0) {
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perror(filename);
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exit(-1);
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}
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signal(SIGINT, stop);
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ret = tracefs_trace_pipe_stream(fd, NULL, SPLICE_F_NONBLOCK);
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close(fd);
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return ret;
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}
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--
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FILES
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-----
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[verse]
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--
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*tracefs.h*
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Header file to include in order to have access to the library APIs.
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*-ltracefs*
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Linker switch to add when building a program that uses the library.
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--
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SEE ALSO
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--------
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*libtracefs*(3),
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*libtraceevent*(3),
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*trace-cmd*(1),
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Documentation/trace/ftrace.rst from the Linux kernel tree
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AUTHOR
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------
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[verse]
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--
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*Steven Rostedt* <rostedt@goodmis.org>
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*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
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--
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REPORTING BUGS
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--------------
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Report bugs to <linux-trace-devel@vger.kernel.org>
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LICENSE
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-------
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libtracefs is Free Software licensed under the GNU LGPL 2.1
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RESOURCES
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---------
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https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
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COPYING
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-------
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Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
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the terms of the GNU Public License (GPL).
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