Provided by: libtracefs-doc_1.8.0-1ubuntu1_all 
NAME
tracefs_instance_get_stat, tracefs_instance_put_stat, tracefs_buffer_stat_entries,
tracefs_buffer_stat_overrun, tracefs_buffer_stat_commit_overrun, tracefs_buffer_stat_bytes,
tracefs_buffer_stat_event_timestamp, tracefs_buffer_stat_timestamp, tracefs_buffer_stat_dropped_events,
tracefs_buffer_stat_read_events - Handling tracing buffer stats
SYNOPSIS
#include <tracefs.h>
struct tracefs_buffer_stat *tracefs_instance_get_stat(struct tracefs_instance *instance, int cpu);
void tracefs_instance_put_stat(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_entries(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_overrun(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_commit_overrun(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_bytes(struct tracefs_buffer_stat *tstat);
long long tracefs_buffer_stat_event_timestamp(struct tracefs_buffer_stat *tstat);
long long tracefs_buffer_stat_timestamp(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_dropped_events(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_read_events(struct tracefs_buffer_stat *tstat);
DESCRIPTION
This set of functions read and parse the tracefs/per_cpu/cpuX/stats file. These files hold the statistics
of the per CPU ring buffer, such as how many events are in the ring buffer, how many have been read and
so on.
The tracefs_instance_get_stat() function will read and parse a given statistics file for a given instance
and cpu. As the ring buffer is split into per_cpu buffers, the information is only associated to the
given cpu. The returned tracefs_buffer_stat pointer can be used with the other tracefs_buffer_stat
functions and must be freed with tracefs_instance_put_stat().
The tracefs_instance_put_stat() will free the resources allocated for the given stat that was created by
tracefs_instance_get_stat().
The tracefs_buffer_stat_entries() returns the number of events that are currently in the ring buffer
associated with tstat.
The tracefs_buffer_stat_overrun() returns the number of events that were lost by the ring buffer writer
overrunning the reader.
The tracefs_buffer_stat_commit_overrun() returns the number of events that were lost because the ring
buffer was too small and an interrupt interrupted a lower context event being recorded and it added more
events than the ring buffer could hold. Note this is not a common occurrence and when it happens it means
that something was not set up properly.
The tracefs_buffer_stat_bytes() returns the number of bytes that the current events take up. Note, it
includes the meta data for the events, but does not include the meta data for the sub-buffers.
The tracefs_buffer_stat_event_timestamp() returns the timestamp of the last event in the ring buffer.
The tracefs_buffer_stat_timestamp() returns the current timestamp of the ring buffer. Note, it is only
read when tracefs_instance_get_stat() is called. It will have the timestamp of the ring buffer when that
function was called.
The tracefs_buffer_stat_dropped_events() returns the number of events that were dropped if overwrite mode
is disabled. It will show the events that were lost because the writer caught up to the reader and could
not write any more events.
The tracefs_buffer_stat_read_events() returns the number of events that were consumed by a reader.
RETURN VALUE
The tracefs_instance_get_stat() returns a tracefs_buffer_stat structure that can be used to retrieve the
statistics via the other functions. It must be freed with tracefs_instance_put_stat().
The other functions that return different values from the tracefs_buffer_stat structure all return the
value, or -1 if the value was not found.
EXAMPLE
#include <stdlib.h>
#include <unistd.h>
#include <tracefs.h>
int main(int argc, char **argv)
{
char *trace;
char buf[1000];
int ret;
int i;
for (i = 0; i < sizeof(buf) - 1; i++) {
buf[i] = '0' + i % 10;
}
buf[i] = '\0';
tracefs_instance_clear(NULL);
for (i = 0; i < 4; i++) {
ret = tracefs_printf(NULL, "%s\n", buf);
if (ret < 0)
perror("write");
}
trace = tracefs_instance_file_read(NULL, "trace", NULL);
printf("%s\n", trace);
free(trace);
for (i = 0; i < sysconf(_SC_NPROCESSORS_CONF); i++) {
struct tracefs_buffer_stat *tstat;
ssize_t entries, eread;
tstat = tracefs_instance_get_stat(NULL, i);
if (!tstat)
continue;
entries = tracefs_buffer_stat_entries(tstat);
eread = tracefs_buffer_stat_read_events(tstat);
if (!entries && !eread) {
tracefs_instance_put_stat(tstat);
continue;
}
printf("CPU: %d\n", i);;
printf("\tentries: %zd\n", entries);
printf("\toverrun: %zd\n", tracefs_buffer_stat_overrun(tstat));
printf("\tcommit_overrun: %zd\n", tracefs_buffer_stat_commit_overrun(tstat));
printf("\tbytes: %zd\n", tracefs_buffer_stat_bytes(tstat));
printf("\tevent_timestamp: %lld\n", tracefs_buffer_stat_event_timestamp(tstat));
printf("\ttimestamp: %lld\n", tracefs_buffer_stat_timestamp(tstat));
printf("\tdropped_events: %zd\n", tracefs_buffer_stat_dropped_events(tstat));
printf("\tread_events: %zd\n", eread);
tracefs_instance_put_stat(tstat);
}
}
FILES
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)
AUTHOR
Steven Rostedt <rostedt@goodmis.org[1]>
REPORTING BUGS
Report bugs to <linux-trace-devel@vger.kernel.org[2]>
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) 2020 VMware, Inc. Free use of this software is granted under the terms of the GNU Public
License (GPL).
NOTES
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
2. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org