tracefs_uprobe_alloc - Man Page

#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)

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).

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.

#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;
}

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) 2022 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

The man page tracefs_uretprobe_alloc(3) is an alias of tracefs_uprobe_alloc(3).