'\" t
.\" Title: libtracefs
.\" Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\" Date: 01/17/2023
.\" Manual: libtracefs Manual
.\" Source: libtracefs 1.6.4
.\" Language: English
.\"
.TH "LIBTRACEFS" "3" "01/17/2023" "libtracefs 1\&.6\&.4" "libtracefs Manual"
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.SH "NAME"
tracefs_instance_file_open, tracefs_instance_file_write, tracefs_instance_file_append, tracefs_instance_file_clear, tracefs_instance_file_read, tracefs_instance_file_read_number \- Work with files in tracing instances\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR
int \fBtracefs_instance_file_open\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR, int \fImode\fR);
int \fBtracefs_instance_file_write\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR, const char *\fIstr\fR);
int \fBtracefs_instance_file_append\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR, const char *\fIstr\fR);
int \fBtracefs_instance_file_clear\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR);
char *\fBtracefs_instance_file_read\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR, int *\fIpsize\fR);
int \fBtracefs_instance_file_read_number\fR(struct tracefs_instance *\fIinstance\fR, const char *\fIfile\fR, long long int *\fIres\fR);
.fi
.SH "DESCRIPTION"
.sp
This set of APIs can be used to work with trace files in all trace instances\&. Each of these APIs take an \fIinstance\fR argument, that can be NULL to act on the top level instance\&. Otherwise, it acts on an instance created with \fBtracefs_insance_create\fR(3)
.sp
The \fBtracefs_instance_file_open()\fR function opens trace \fIfile\fR from given \fIinstance\fR and returns a file descriptor to it\&. The file access \fImode\fR can be specified, see \fBopen\fR(3) for more details\&. If \-1 is passed as \fImode\fR, default O_RDWR is used\&.
.sp
The \fBtracefs_instance_file_write()\fR function writes a string \fIstr\fR in a \fIfile\fR from the given \fIinstance\fR, without the terminating NULL character\&. When opening the file, this function tries to truncates the size of the file to zero, which clears all previously existing settings\&.
.sp
The \fBtracefs_instance_file_append()\fR function writes a string \fIstr\fR in a \fIfile\fR from the given \fIinstance\fR, without the terminating NULL character\&. This function is similar to \fBtracefs_instance_file_write()\fR, but the existing content of the is not cleared\&. Thus the new settings are appended to the existing ones (if any)\&.
.sp
The \fBtracefs_instance_file_clear()\fR function tries to truncates the size of the file to zero, which clears all previously existing settings\&. If the file has content that does not get cleared in this way, this will not have any effect\&.
.sp
The \fBtracefs_instance_file_read()\fR function reads the content of a \fIfile\fR from the given \fIinstance\fR\&.
.sp
The \fBtracefs_instance_file_read_number()\fR function reads the content of a \fIfile\fR from the given \fIinstance\fR and converts it to a long long integer, which is stored in \fIres\fR\&.
.SH "RETURN VALUE"
.sp
The \fBtracefs_instance_file_open()\fR function returns a file descriptor to the opened file\&. It must be closed with \fBclose\fR(3)\&. In case of an error, \-1 is returned\&.
.sp
The \fBtracefs_instance_file_write()\fR function returns the number of written bytes, or \-1 in case of an error\&.
.sp
The \fBtracefs_instance_file_append()\fR function returns the number of written bytes, or \-1 in case of an error\&.
.sp
The \fBtracefs_instance_file_clear()\fR function returns 0 on success, or \-1 in case of an error\&.
.sp
The \fBtracefs_instance_file_read()\fR function returns a pointer to a NULL terminated string, read from the file, or NULL in case of an error\&. The returned string must be freed with free()\&.
.sp
The \fBtracefs_instance_file_read_number()\fR function returns 0 if a valid integer is read from the file and stored in \fIres\fR or \-1 in case of an error\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
#include <tracefs\&.h>
struct tracefs_instance *inst = tracefs_instance_create("foo");
if (!inst) {
/* Error creating a new trace instance */
\&.\&.\&.
}
if (tracefs_file_exists(inst,"trace_clock")) {
/* The instance foo supports trace clock */
char *path, *clock;
int size;
path = = tracefs_instance_get_file(inst, "trace_clock")
if (!path) {
/* Error getting the path to trace_clock file in instance foo */
\&.\&.\&.
}
\&.\&.\&.
tracefs_put_tracing_file(path);
clock = tracefs_instance_file_read(inst, "trace_clock", &size);
if (!clock) {
/* Failed to read trace_clock file in instance foo */
\&.\&.\&.
}
\&.\&.\&.
free(clock);
if (tracefs_instance_file_write(inst, "trace_clock", "global") != strlen("global")) {
/* Failed to set gloabl trace clock in instance foo */
\&.\&.\&.
}
} else {
/* The instance foo does not support trace clock */
}
if (tracefs_dir_exists(inst,"options")) {
/* The instance foo supports trace options */
char *path = tracefs_instance_get_file(inst, "options");
if (!path) {
/* Error getting the path to options directory in instance foo */
\&.\&.\&.
}
tracefs_put_tracing_file(path);
} else {
/* The instance foo does not support trace options */
}
\&.\&.\&.
if (tracefs_instance_is_new(inst))
tracefs_instance_destroy(inst);
else
tracefs_instance_free(inst);
\&.\&.\&.
long long int res;
if (tracefs_instance_file_read_number(NULL, "tracing_on", &res) == 0) {
if (res == 0) {
/* tracing is disabled in the top instance */
} else if (res == 1) {
/* tracing is enabled in the top instance */
} else {
/* Unknown tracing state of the top instance */
}
} else {
/* Failed to read integer from tracing_on file */
}
\&.\&.\&.
int fd;
fd = tracefs_instance_file_open(NULL, "tracing_on", O_WRONLY);
if (fd >= 0) {
/* Got file descriptor to the tracing_on file from the top instance for writing */
\&.\&.\&.
close(fd);
}
.fi
.if n \{\
.RE
.\}
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtracefs\&.h\fR
Header file to include in order to have access to the library APIs\&.
\fB\-ltracefs\fR
Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBlibtracefs\fR(3), \fBlibtraceevent\fR(3), \fBtrace\-cmd\fR(1)
.SH "AUTHOR"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBSteven Rostedt\fR <\m[blue]\fBrostedt@goodmis\&.org\fR\m[]\&\s-2\u[1]\d\s+2>
\fBTzvetomir Stoyanov\fR <\m[blue]\fBtz\&.stoyanov@gmail\&.com\fR\m[]\&\s-2\u[2]\d\s+2>
.fi
.if n \{\
.RE
.\}
.SH "REPORTING BUGS"
.sp
Report bugs to <\m[blue]\fBlinux\-trace\-devel@vger\&.kernel\&.org\fR\m[]\&\s-2\u[3]\d\s+2>
.SH "LICENSE"
.sp
libtracefs is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/libs/libtrace/libtracefs\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2020 VMware, Inc\&. Free use of this software is granted under the terms of the GNU Public License (GPL)\&.
.SH "NOTES"
.IP " 1." 4
rostedt@goodmis.org
.RS 4
\%mailto:rostedt@goodmis.org
.RE
.IP " 2." 4
tz.stoyanov@gmail.com
.RS 4
\%mailto:tz.stoyanov@gmail.com
.RE
.IP " 3." 4
linux-trace-devel@vger.kernel.org
.RS 4
\%mailto:linux-trace-devel@vger.kernel.org
.RE