Documentation/libtracefs-guest.txt

libtracefs(3)
=============

NAME
----
tracefs_find_cid_pid, tracefs_instance_find_cid_pid, tracefs_time_conversion -
helper functions to handle tracing guests

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

char pass:[*]*tracefs_find_cid_pid*(int _cid_);
char pass:[*]*tracefs_instance_find_cid_pid*(struct tracefs_instance pass:[*]_instance_, int _cid_);
int *tracefs_time_conversion*(int _cpu_, int pass:[*]_shift_, int pass:[*]_multi_, long long pass:[*]offset);
--

DESCRIPTION
-----------
The *tracefs_find_cid_pid*() will use tracing to follow the wakeups of connecting to
the given _cid_ in order to find the pid of the guest thread that belongs to the vsocket cid.
It will then read the proc file system to find the thread leader, and it will return
the pid of the thread leader.

The *tracefs_instance_find_cid_pid*() is the same as *tracefs_find_cid_pid*() but defines
the instance to use to perform the tracing in. If NULL it will use the top level
buffer to perform the tracing.

The *tracefs_time_conversion*() will return the values used by the kernel to convert
the raw time stamp counter into nanoseconds for the given _cpu_. Pointers for _shift_, _multi_
and _offset_ can be NULL to be ignored, otherwise they are set with the shift, multiplier
and offset repectively.

RETURN VALUE
------------
Both *tracefs_find_cid_pid*() and *tracefs_instance_find_cid_pid*() will return the
pid of the guest main thread that belongs to the _cid_, or -1 on error (or not found).

EXAMPLE
-------
[source,c]
--
#include <stdlib.h>
#include <unistd.h>
#include <tracefs.h>

#define MAX_CID		256

static void find_cid(struct tracefs_instance *instance, int cid)
{
	int pid;

	pid = tracefs_instance_find_cid_pid(instance, cid);
	if (pid >= 0)
		printf("%d\t%d\n", cid, pid);
}

static int find_cids(void)
{
	struct tracefs_instance *instance;
	char *name;
	int cid;
	int ret;

	ret = asprintf(&name, "vsock_find-%d\n", getpid());
	if (ret < 0)
		return ret;

	instance = tracefs_instance_create(name);
	free(name);
	if (!instance)
		return -1;

	for (cid = 0; cid < MAX_CID; cid++)
		find_cid(instance, cid);

	tracefs_event_disable(instance, NULL, NULL);
	tracefs_instance_destroy(instance);
	tracefs_instance_free(instance);
	return 0;
}

struct time_info {
	int		shift;
	int		multi;
};

static void show_time_conversion(void)
{
	struct time_info *tinfo;
	int cpus;
	int cpu;
	int ret;

	cpus = sysconf(_SC_NPROCESSORS_CONF);
	tinfo = calloc(cpus, sizeof(*tinfo));
	if (!tinfo)
		exit(-1);

	for (cpu = 0; cpu < cpus; cpu++) {
		ret  = tracefs_time_conversion(cpu,
						&tinfo[cpu].shift,
						&tinfo[cpu].multi,
						NULL);
		if (ret)
			break;
	}
	if (cpu != cpus) {
		if (!cpu) {
			perror("tracefs_time_conversion");
			exit(-1);
		}
		printf("Only read %d of %d CPUs", cpu, cpus);
		cpus = cpu + 1;
	}

	/* Check if all the shift and mult values are the same */
	for (cpu = 1; cpu < cpus; cpu++) {
		if (tinfo[cpu - 1].shift != tinfo[cpu].shift)
			break;
		if (tinfo[cpu - 1].multi != tinfo[cpu].multi)
			break;
	}

	if (cpu == cpus) {
		printf("All cpus have:\n");
		printf(" shift:  %d\n", tinfo[0].shift);
		printf(" multi:  %d\n", tinfo[0].multi);
		printf("\n");
		return;
	}

	for (cpu = 0; cpu < cpus; cpu++) {
		printf("CPU: %d\n", cpu);
		printf(" shift:  %d\n", tinfo[cpu].shift);
		printf(" multi:  %d\n", tinfo[cpu].multi);
		printf("\n");
	}
}

int main(int argc, char *argv[])
{
	show_time_conversion();
	find_cids();
	exit(0);
}
--
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)

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) 2020 VMware, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).