LIBTRACEFS(3)

NAME
tracefs_uprobe_alloc, tracefs_uretprobe_alloc - Allocate new user (return) probe

SYNOPSIS

#include <tracefs.h>

struct tracefs_dynevent *
tracefs_uprobe_alloc(const char *system, const char *event,
                     const char *file, unsigned long long offset, const char *fetchargs)
struct tracefs_dynevent *
tracefs_uretprobe_alloc(const char *system, const char *event,
                     const char *file, unsigned long long offset, const char *fetchargs)

DESCRIPTION

tracefs_uprobe_alloc() allocates a new uprobe context. It will be in the system group (or uprobes if system is NULL) and with event name. The uprobe will be attached to offset within the file. The list of arguments, described in fetchargs, will be fetched with the uprobe. The returned pointer to the user probe context must be freed with tracefs_dynevent_free(). The ubrobe is not configured in the system, tracefs_dynevent_* set of APIs can be used to configure it.

The tracefs_uretprobe_alloc() behaves the same as tracefs_uprobe_alloc(), the only difference is that it allocates context to user return probe (uretprobe).

RETURN VALUE

The tracefs_uprobe_alloc() and tracefs_uretprobe_alloc() APIs return a pointer to an allocated tracefs_dynevent structure, describing the user probe. This pointer must be freed with tracefs_dynevent_free(3). Note, this only allocates a descriptor representing the uprobe. It does not modify the running system. On error NULL is returned.

EXAMPLE

    #include <stdlib.h>
    #include <unistd.h>
    #include <sys/wait.h>

    #include <tracefs.h>

    static int callback(struct tep_event *event, struct tep_record *record,
                        int cpu, void *data)
    {
            struct trace_seq seq;

            trace_seq_init(&seq);
            tep_print_event(event->tep, &seq, record, "%d-%s: %s",
                            TEP_PRINT_PID, TEP_PRINT_COMM, TEP_PRINT_NAME);
            trace_seq_puts(&seq, "'\n");

            trace_seq_terminate(&seq);
            trace_seq_do_printf(&seq);
            trace_seq_destroy(&seq);

            return 0;
    }

    static pid_t run_exec(char **argv, char **env)
    {
            pid_t pid;

            pid = fork();
            if (pid)
                    return pid;

            execve(argv[0], argv, env);
            perror("exec");
            exit(-1);
    }

    const char *myprobe = "my_urobes";

    int main (int argc, char **argv, char **env)
    {
            struct tracefs_dynevent *uprobe, *uretprobe;
            struct tep_handle *tep;
            struct tracefs_instance *instance;
            const char *sysnames[] = { myprobe, NULL };
            long addr;
            pid_t pid;

            if (argc < 3) {
                    printf("usage: %s file_offset command\n", argv[0]);
                    exit(-1);
            }
            addr = strtol(argv[1], NULL, 0);

            instance = tracefs_instance_create("exec_open");
            if (!instance) {
                    perror("creating instance");
                    exit(-1);
            }

            tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_UPROBE|TRACEFS_DYNEVENT_URETPROBE, true);

            uprobe = tracefs_uprobe_alloc(myprobe, "user_probe", argv[2], addr, NULL);
            uretprobe = tracefs_uretprobe_alloc(myprobe, "user_retprobe", argv[2], addr, NULL);
            if (!uprobe || !uretprobe) {
                    perror("allocating user probes");
                    exit(-1);
            }

            if (tracefs_dynevent_create(uprobe) ||
                tracefs_dynevent_create(uretprobe)) {
                    perror("creating user probes");
                    exit(-1);
            }

            tep = tracefs_local_events_system(NULL, sysnames);
            if (!tep) {
                    perror("reading events");
                    exit(-1);
            }

            tracefs_event_enable(instance, myprobe, "user_probe");
            tracefs_event_enable(instance, myprobe, "user_retprobe");

            pid = run_exec(&argv[2], env);

            /* Let the child start to run */
            sched_yield();

            do {
                    tracefs_load_cmdlines(NULL, tep);
                    tracefs_iterate_raw_events(tep, instance, NULL, 0, callback, NULL);
            } while (waitpid(pid, NULL, WNOHANG) != pid);

            /* disable and destroy the events */
            tracefs_dynevent_destroy(uprobe, true);
            tracefs_dynevent_destroy(uretprobe, true);
            tracefs_dynevent_free(uprobe);
            tracefs_dynevent_free(uretprobe);
            tracefs_instance_destroy(instance);

            return 0;
    }

FILES

    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

    Steven Rostedt <rostedt@goodmis.org[1]>
    Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>

REPORTING BUGS

Report bugs to <linux-trace-devel@vger.kernel.org[3]>

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) 2022 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).

NOTES

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