'\" t
.\" Title: libtracefs
.\" Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot
.\" Date: 01/13/2024
.\" Manual: libtracefs Manual
.\" Source: libtracefs 1.8.0
.\" Language: English
.\"
.TH "LIBTRACEFS" "3" "01/13/2024" "libtracefs 1\&.8\&.0" "libtracefs Manual"
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
tracefs_instance_get_subbuf_size, tracefs_instance_set_subbuf_size \- Helper functions for working with ring buffer sub buffers\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include \fR
size_t \fBtracefs_instance_get_subbuf_size\fR(struct tracefs_instance *\fIinstance\fR);
int \fBtracefs_instance_set_subbuf_size\fR(struct tracefs_instance *\fIinstance\fR, size_t \fIsize\fR);
.fi
.SH "DESCRIPTION"
.sp
Helper functions for working with the sub\-buffers of the tracing ring buffer\&. The tracing ring buffer is broken up into \fBsub\-buffers\fR\&. An event can not be bigger than the data section of the sub\-buffer (see \fBtep_get_sub_buffer_data_size\fR(3))\&. By default, the ring buffer uses the architectures \fBpage_size\fR as the default size of the sub\-buffer, but this can be limiting if there is a need for large events, for example, the application wants to write large strings into the trace_marker file\&.
.sp
The \fBtracefs_instance_get_subbuf_size()\fR returns the current size in kilobytes fo the ring buffer sub\-buffers\&.
.sp
The \fBtracefs_instance_set_subbuf_size()\fR will write the size in kilobytes of what the new sub\-buffer size should be\&. Note, that this is only a hint to what the minimum sub\-buffer size should be\&. It also does not take into account the meta\-data that is used by the sub\-buffer, so the size written should be no less than 16 bytes more than the maximum event size that will be used\&. The kernel will likely make the sub\-buffer size larger than specified, as it may need to align the size for implementation purposes\&.
.SH "RETURN VALUE"
.sp
The \fBtracefs_instance_get_subbuf_size()\fR returns the size of the current sub\-buffer for the given \fIinstance\fR ring buffer or \-1 on error\&.
.sp
The \fBtracefs_instance_set_subbuf_size()\fR will return 0 if it successfully set the \fIinstance\fR ring buffer sub\-buffer size in kilobytes, or \-1 on error\&.
.SH "EXAMPLE"
.sp
.if n \{\
.RS 4
.\}
.nf
#include
#include
#include
int main(int argc, char **argv)
{
struct tep_handle *tep;
ssize_t save_subsize;
ssize_t subsize;
char *trace;
char buf[3000];
int meta_size;
int ret;
int i;
tep = tep_alloc();
ret = tracefs_load_headers(NULL, tep);
tep_free(tep);
if (ret < 0) {
perror("reading headers");
exit(\-1);
}
meta_size = tep_get_sub_buffer_size(tep) \- tep_get_sub_buffer_data_size(tep);
save_subsize = tracefs_instance_get_subbuf_size(NULL);
if (save_subsize < 0) {
printf("Changing sub\-buffer size not available\en");
exit(\-1);
}
subsize = save_subsize * 1024;
/* Have at least 4 writes fit on a sub\-buffer */
if (subsize \- meta_size < sizeof(buf) *4 ) {
subsize = ((sizeof(buf) * 4 + meta_size) + 1023) / 1024;
tracefs_instance_set_subbuf_size(NULL, subsize);
}
for (i = 0; i < sizeof(buf) \- 1; i++) {
buf[i] = \*(Aq0\*(Aq + i % 10;
}
buf[i] = \*(Aq\e0\*(Aq;
tracefs_instance_clear(NULL);
for (i = 0; i < 4; i++) {
ret = tracefs_printf(NULL, "%s\en", buf);
if (ret < 0)
perror("write");
}
trace = tracefs_instance_file_read(NULL, "trace", NULL);
printf("%s\en", trace);
free(trace);
printf("Buffer size was: %zd * 1024\en",
tracefs_instance_get_subbuf_size(NULL));
tracefs_instance_set_subbuf_size(NULL, save_subsize);
}
.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