# libtraceevent(3) Manual Page

## NAME

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

## SYNOPSIS

    #include <event-parse.h>

    int tep_register_comm(struct tep_handle *tep, const char *comm, int pid);
    int tep_override_comm(struct tep_handle *tep, const char *comm, int pid);
    bool tep_is_pid_registered(struct tep_handle *tep, int pid);
    const char *tep_data_comm_from_pid(struct tep_handle *pevent, int pid);
    struct cmdline *tep_data_pid_from_comm(struct tep_handle *pevent, const char *comm, struct cmdline *next);
    int tep_cmdline_pid(struct tep_handle *pevent, struct cmdline *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:

    #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

    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

    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/libs/libtrace/libtraceevent.git/