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NAME | SYNOPSIS | DESCRIPTION | FLAGS | RETURN VALUE | ERRORS | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
tracefs_function_filter, tracefs_function_notrace,
tracefs_filter_functions - Functions to modify the the function
trace filters
#include <tracefs.h>
int tracefs_function_filter(struct tracefs_instance *instance, const char *filter, const char *module, int flags);
int tracefs_function_notrace(struct tracefs_instance *instance, const char *filter, const char *module, int flags);
int tracefs_filter_functions(const char *filter, const char *module, char ***list);
tracefs_function_filter and tracefs_function_notrace can be used
to limit the Linux kernel functions that would be traced by the
function and function-graph tracers. The tracefs_function_filter
defines a list of functions that can be traced. The
tracefs_function_notrace defines a list of functions that will not
be traced. If a function is in both lists, it will not be traced.
They take an instance , that can be NULL for the top level
tracing, filter, a string that represents a filter that should be
applied to define what functions are to be traced, module, to
limit the filtering on a specific module (or NULL to filter on all
functions), flags which holds control knobs on how the filters
will be handled (see FLAGS) section below.
The tracefs_filter_functions returns a list of functions that can
be filtered on via the filter and module that are supplied. If
both filter and module are NULL then, all available functions that
can be filtered is returned. On success, list must be freed with
tracefs_list_free()(3).
The filter may be either a straight match of a function, a glob or
regex(3). A glob is where * matches zero or more characters, ?
will match zero or one character, and . only matches a period. If
the filter is determined to be a regex (where it contains anything
other than alpha numeric characters, or ., *, ?) the filter will
be processed as a regex(3) following the rules of regex(3), and .
is not a period, but will match any one character. To force a
regular expression, either prefix filter with a ^ or append it
with a $ as the filter does complete matches of the functions
anyway.
If module is set and filter is NULL, this will imply the same as
filter being equal to "*". Which will enable all functions for a
given module. Otherwise the filter may be NULL if a previous call
to tracefs_function_filter() with the same instance had
TRACEFS_FL_CONTINUE set and this call does not. This is useful to
simply commit the previous filters. It may also be NULL if
TRACEFS_FL_RESET is set and the previous call did not have the
same instance and TRACEFS_FL_CONTINUE set. This is useful to just
clear the filter.
The flags parameter may have the following set, or be zero.
TRACEFS_FL_RESET : If flags contains TRACEFS_FL_RESET, then it
will clear the filters that are currently set before applying
filter. Otherwise, filter is added to the current set of filters
already enabled. If this flag is set and the previous call to
tracefs_function_filter() had the same instance and the
TRACEFS_FL_CONTINUE flag was set, then the function will fail with
a return of -1 and errno set to EBUSY.
TRACEFS_FL_CONTINUE : If flags contains TRACEFS_FL_CONTINUE, then
filter will not take effect after a successful call to
tracefs_function_filter(). This allows for multiple calls to
tracefs_function_filter() to update the filter function and then a
single call (one without the TRACEFS_FL_CONTINUE flag set) to
commit all the filters. It can be called multiple times to add
more filters. A call without this flag set will commit the changes
before returning (if the filter passed in successfully matched). A
tracefs_function_filter() call after one that had the
TRACEFS_FL_CONTINUE flag set for the same instance will fail if
TRACEFS_FL_RESET flag is set, as the reset flag is only applicable
for the first filter to be added before committing.
TRACEFS_FL_FUTURE : If flags contains TRACEFS_FL_FUTURE and module
holds a string of a module, then if the module is not loaded it
will attemp to write the filter with the module in the filter
file. Starting in Linux v4.13 module functions could be added to
the filter before they are loaded. The filter will be cached, and
when the module is loaded, the filter will be set before the
module executes, allowing to trace init functions of a module.
This will only work if the filter is not a regular expression.
For tracefs_function_filter() and tracefs_function_notrace() a
return of 0 means success. If the there is an error but the
filtering was not started, then 1 is returned. If filtering was
started but an error occurs, then -1 is returned. The state of the
filtering may be in an unknown state.
If TRACEFS_FL_CONTINUE was set, and 0 or -1 was returned, then
another call to tracefs_function_filter() must be done without
TRACEFS_FL_CONTINUE set in order to commit (and close) the
filtering.
For tracefs_filter_functions(), a return of 0 means success, and
the list parameter is filled with a list of function names that
matched filter and module. list is a string array, where the last
string pointer in the array is NULL. The list must be freed with
tracefs_list_free(). On failure, a negative is returned, and list
is ignored.
tracefs_function_filter() can fail with the following errors:
EINVAL The filter is invalid or did not match any functions.
EBUSY The previous call of tracefs_function_filter() was called
with the same instance and TRACEFS_FL_CONTINUE set and the current
call had TRACEFS_FL_RESET set.
Other errors may also happen caused by internal system calls.
#include <stdio.h>
#include <errno.h>
#include <tracefs.h>
#define INST "dummy"
static const char *filters[] = { "run_init_process", "try_to_run_init_process", "dummy1", NULL };
int main(int argc, char *argv[])
{
struct tracefs_instance *inst = tracefs_instance_create(INST);
char **func_list;
int ret;
int i;
if (!inst) {
/* Error creating new trace instance */
}
if (tracefs_filter_functions("*lock*", NULL, &func_list) < 0) {
printf("Failed to read filter functions\n");
goto out;
}
printf("Ignoring the following functions:\n");
for (i = 0; func_list[i]; i++)
printf(" %s\n", func_list[i]);
tracefs_list_free(func_list);
/* Do not trace any function with the word "lock" in it */
ret = tracefs_function_notrace(inst, "*lock*", NULL, TRACEFS_FL_RESET);
if (ret) {
printf("Failed to set the notrace filter\n");
goto out;
}
/* First reset the filter */
ret = tracefs_function_filter(inst, NULL, NULL,
TRACEFS_FL_RESET | TRACEFS_FL_CONTINUE);
if (ret) {
printf("Failed to reset the filter\n");
/* Make sure it is closed, -1 means filter was started */
if (ret < 0)
tracefs_function_filter(inst, NULL, NULL, 0);
}
for (i = 0; filters[i]; i++) {
ret = tracefs_function_filter(inst, filters[i], NULL,
TRACEFS_FL_CONTINUE);
if (ret) {
if (errno == EINVAL)
printf("Filter %s did not match\n", filters[i]);
else
printf("Failed writing %s\n", filters[i]);
}
}
ret = tracefs_function_filter(inst, "*", "ext4", 0);
if (ret) {
printf("Failed to set filters for ext4\n");
/* Force the function to commit previous filters */
tracefs_function_filter(inst, NULL, NULL, 0);
}
out:
tracefs_instance_destroy(inst);
return ret;
}
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]>
sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>
Report bugs to <linux-trace-devel@vger.kernel.org[4]>
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. sameeruddin.shaik8@gmail.com
mailto:sameeruddin.shaik8@gmail.com
4. 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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