1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
|
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 *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
-------
[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).
|
