liblttng-ust-fork/ustfork.c

   1 /*
   2  * Copyright (C) 2009  Pierre-Marc Fournier
   3  * Copyright (C) 2011  Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; version 2.1 of
   8  * the License.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  18  */
  19
  20 #define _GNU_SOURCE
  21 #include <dlfcn.h>
  22 #include <unistd.h>
  23 #include <stdio.h>
  24 #include <signal.h>
  25 #include <sched.h>
  26 #include <stdarg.h>
  27 #include "usterr.h"
  28
  29 #include <lttng/ust.h>
  30
  31 struct user_desc;
  32
  33 pid_t fork(void)
  34 {
  35         static pid_t (*plibc_func)(void) = NULL;
  36         sigset_t sigset;
  37         pid_t retval;
  38
  39         if (plibc_func == NULL) {
  40                 plibc_func = dlsym(RTLD_NEXT, "fork");
  41                 if (plibc_func == NULL) {
  42                         fprintf(stderr, "libustfork: unable to find \"fork\" symbol\n");
  43                         return -1;
  44                 }
  45         }
  46
  47         ust_before_fork(&sigset);
  48         /* Do the real fork */
  49         retval = plibc_func();
  50         if (retval == 0) {
  51                 /* child */
  52                 ust_after_fork_child(&sigset);
  53         } else {
  54                 ust_after_fork_parent(&sigset);
  55         }
  56         return retval;
  57 }
  58
  59 struct ustfork_clone_info {
  60         int (*fn)(void *);
  61         void *arg;
  62         sigset_t sigset;
  63 };
  64
  65 static int clone_fn(void *arg)
  66 {
  67         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
  68
  69         /* clone is now done and we are in child */
  70         ust_after_fork_child(&info->sigset);
  71         return info->fn(info->arg);
  72 }
  73
  74 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
  75 {
  76         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
  77                         int flags, void *arg, pid_t *ptid,
  78                         struct user_desc *tls, pid_t *ctid) = NULL;
  79         /* var args */
  80         pid_t *ptid;
  81         struct user_desc *tls;
  82         pid_t *ctid;
  83         /* end of var args */
  84         va_list ap;
  85         int retval;
  86
  87         va_start(ap, arg);
  88         ptid = va_arg(ap, pid_t *);
  89         tls = va_arg(ap, struct user_desc *);
  90         ctid = va_arg(ap, pid_t *);
  91         va_end(ap);
  92
  93         if (plibc_func == NULL) {
  94                 plibc_func = dlsym(RTLD_NEXT, "clone");
  95                 if (plibc_func == NULL) {
  96                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
  97                         return -1;
  98                 }
  99         }
 100
 101         if (flags & CLONE_VM) {
 102                 /*
 103                  * Creating a thread, no need to intervene, just pass on
 104                  * the arguments.
 105                  */
 106                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 107                                 tls, ctid);
 108         } else {
 109                 /* Creating a real process, we need to intervene. */
 110                 struct ustfork_clone_info info = { fn: fn, arg: arg };
 111
 112                 ust_before_fork(&info.sigset);
 113                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 114                                 ptid, tls, ctid);
 115                 /* The child doesn't get here. */
 116                 ust_after_fork_parent(&info.sigset);
 117         }
 118         return retval;
 119 }