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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
tracefs_find_cid_pid, tracefs_instance_find_cid_pid,
tracefs_time_conversion - helper functions to handle tracing
guests
#include <tracefs.h>
char *tracefs_find_cid_pid(int cid);
char *tracefs_instance_find_cid_pid(struct tracefs_instance *instance, int cid);
int tracefs_time_conversion(int cpu, int *shift, int *multi, long long *offset);
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.
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).
#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);
}
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.
libtracefs(3), libtraceevent(3), trace-cmd(1)
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
Report bugs to <linux-trace-devel@vger.kernel.org[3]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2020 VMware, Inc. Free use of this software is
granted under the terms of the GNU Public License (GPL).
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
2. tz.stoyanov@gmail.com
mailto:tz.stoyanov@gmail.com
3. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org
This page is part of the libtracefs (Linux kernel trace file
system library) project. Information about the project can be
found at ⟨https://www.trace-cmd.org/⟩. If you have a bug report
for this manual page, see ⟨https://www.trace-cmd.org/⟩. This page
was obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-02.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
libtracefs 1.7.0 12/22/2023 LIBTRACEFS(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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