xref: /kernel/linux/linux-5.10/tools/lib/traceevent/Documentation/libtraceevent-commands.txt (revision 8c2ecf20)

libtraceevent(3)
================

NAME
----
tep_register_comm, tep_override_comm, tep_pid_is_registered,
tep_data_comm_from_pid, tep_data_pid_from_comm, tep_cmdline_pid -
Manage pid to process name mappings.

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

int *tep_register_comm*(struct tep_handle pass:[*]_tep_, const char pass:[*]_comm_, int _pid_);
int *tep_override_comm*(struct tep_handle pass:[*]_tep_, const char pass:[*]_comm_, int _pid_);
bool *tep_is_pid_registered*(struct tep_handle pass:[*]_tep_, int _pid_);
const char pass:[*]*tep_data_comm_from_pid*(struct tep_handle pass:[*]_pevent_, int _pid_);
struct cmdline pass:[*]*tep_data_pid_from_comm*(struct tep_handle pass:[*]_pevent_, const char pass:[*]_comm_, struct cmdline pass:[*]_next_);
int *tep_cmdline_pid*(struct tep_handle pass:[*]_pevent_, struct cmdline pass:[*]_cmdline_);
--

DESCRIPTION
-----------
These functions can be used to handle the mapping between pid and process name.
The library builds a cache of these mappings, which is used to display the name
of the process, instead of its pid. This information can be retrieved from
tracefs/saved_cmdlines file.

The _tep_register_comm()_ function registers a _pid_ / process name mapping.
If a command with the same _pid_ is already registered, an error is returned.
The _pid_ argument is the process ID, the _comm_ argument is the process name,
_tep_ is the event context. The _comm_ is duplicated internally.

The _tep_override_comm()_ function registers a _pid_ / process name mapping.
If a process with the same pid is already registered, the process name string is
udapted with the new one. The _pid_ argument is the process ID, the _comm_
argument is the process name, _tep_ is the event context. The _comm_ is
duplicated internally.

The _tep_is_pid_registered()_ function checks if a pid has a process name
mapping registered. The _pid_ argument is the process ID, _tep_ is the event
context.

The _tep_data_comm_from_pid()_ function returns the process name for a given
pid. The _pid_ argument is the process ID, _tep_ is the event context.
The returned string should not be freed, but will be freed when the _tep_
handler is closed.

The _tep_data_pid_from_comm()_ function returns a pid for a given process name.
The _comm_ argument is the process name, _tep_ is the event context.
The argument _next_ is the cmdline structure to search for the next pid.
As there may be more than one pid for a given process, the result of this call
can be passed back into a recurring call in the _next_ parameter, to search for
the next pid. If _next_ is NULL, it will return the first pid associated with
the _comm_. The function performs a linear search, so it may be slow.

The _tep_cmdline_pid()_ function returns the pid associated with a given
_cmdline_. The _tep_ argument is the event context.

RETURN VALUE
------------
_tep_register_comm()_ function returns 0 on success. In case of an error -1 is
returned and errno is set to indicate the cause of the problem: ENOMEM, if there
is not enough memory to duplicate the _comm_ or EEXIST if a mapping for this
_pid_ is already registered.

_tep_override_comm()_ function returns 0 on success. In case of an error -1 is
returned and errno is set to indicate the cause of the problem: ENOMEM, if there
is not enough memory to duplicate the _comm_.

_tep_is_pid_registered()_ function returns true if the _pid_ has a process name
mapped to it, false otherwise.

_tep_data_comm_from_pid()_ function returns the process name as string, or the
string "<...>" if there is no mapping for the given pid.

_tep_data_pid_from_comm()_ function returns a pointer to a struct cmdline, that
holds a pid for a given process, or NULL if none is found. This result can be
passed back into a recurring call as the _next_ parameter of the function.

_tep_cmdline_pid()_ functions returns the pid for the give cmdline. If _cmdline_
 is NULL, then -1 is returned.

EXAMPLE
-------
The following example registers pid for command "ls", in context of event _tep_
and performs various searches for pid / process name mappings:
[source,c]
--
#include <event-parse.h>
...
int ret;
int ls_pid = 1021;
struct tep_handle *tep = tep_alloc();
...
	ret = tep_register_comm(tep, "ls", ls_pid);
	if (ret != 0 && errno == EEXIST)
		ret = tep_override_comm(tep, "ls", ls_pid);
	if (ret != 0) {
		/* Failed to register pid / command mapping */
	}
...
	if (tep_is_pid_registered(tep, ls_pid) == 0) {
		/* Command mapping for ls_pid is not registered */
	}
...
	const char *comm = tep_data_comm_from_pid(tep, ls_pid);
	if (comm) {
		/* Found process name for ls_pid */
	}
...
	int pid;
	struct cmdline *cmd = tep_data_pid_from_comm(tep, "ls", NULL);
	while (cmd) {
		pid = tep_cmdline_pid(tep, cmd);
		/* Found pid for process "ls" */
		cmd = tep_data_pid_from_comm(tep, "ls", cmd);
	}
--
FILES
-----
[verse]
--
*event-parse.h*
	Header file to include in order to have access to the library APIs.
*-ltraceevent*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
_libtraceevent(3)_, _trace-cmd(1)_

AUTHOR
------
[verse]
--
*Steven Rostedt* <rostedt@goodmis.org>, author of *libtraceevent*.
*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>, author of this man page.
--
REPORTING BUGS
--------------
Report bugs to  <linux-trace-devel@vger.kernel.org>

LICENSE
-------
libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git