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 pid_t fork(void)
  32 {
  33         static pid_t (*plibc_func)(void) = NULL;
  34         sigset_t sigset;
  35         pid_t retval;
  36
  37         if (plibc_func == NULL) {
  38                 plibc_func = dlsym(RTLD_NEXT, "fork");
  39                 if (plibc_func == NULL) {
  40                         fprintf(stderr, "libustfork: unable to find \"fork\" symbol\n");
  41                         return -1;
  42                 }
  43         }
  44
  45         ust_before_fork(&sigset);
  46         /* Do the real fork */
  47         retval = plibc_func();
  48         if (retval == 0) {
  49                 /* child */
  50                 ust_after_fork_child(&sigset);
  51         } else {
  52                 ust_after_fork_parent(&sigset);
  53         }
  54         return retval;
  55 }
  56
  57 #ifdef __linux__
  58
  59 struct user_desc;
  60
  61 struct ustfork_clone_info {
  62         int (*fn)(void *);
  63         void *arg;
  64         sigset_t sigset;
  65 };
  66
  67 static int clone_fn(void *arg)
  68 {
  69         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
  70
  71         /* clone is now done and we are in child */
  72         ust_after_fork_child(&info->sigset);
  73         return info->fn(info->arg);
  74 }
  75
  76 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
  77 {
  78         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
  79                         int flags, void *arg, pid_t *ptid,
  80                         struct user_desc *tls, pid_t *ctid) = NULL;
  81         /* var args */
  82         pid_t *ptid;
  83         struct user_desc *tls;
  84         pid_t *ctid;
  85         /* end of var args */
  86         va_list ap;
  87         int retval;
  88
  89         va_start(ap, arg);
  90         ptid = va_arg(ap, pid_t *);
  91         tls = va_arg(ap, struct user_desc *);
  92         ctid = va_arg(ap, pid_t *);
  93         va_end(ap);
  94
  95         if (plibc_func == NULL) {
  96                 plibc_func = dlsym(RTLD_NEXT, "clone");
  97                 if (plibc_func == NULL) {
  98                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
  99                         return -1;
 100                 }
 101         }
 102
 103         if (flags & CLONE_VM) {
 104                 /*
 105                  * Creating a thread, no need to intervene, just pass on
 106                  * the arguments.
 107                  */
 108                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 109                                 tls, ctid);
 110         } else {
 111                 /* Creating a real process, we need to intervene. */
 112                 struct ustfork_clone_info info = { fn: fn, arg: arg };
 113
 114                 ust_before_fork(&info.sigset);
 115                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 116                                 ptid, tls, ctid);
 117                 /* The child doesn't get here. */
 118                 ust_after_fork_parent(&info.sigset);
 119         }
 120         return retval;
 121 }
 122
 123 #elif defined (__FreeBSD__)
 124
 125 pid_t rfork(int flags)
 126 {
 127         static pid_t (*plibc_func)(void) = NULL;
 128         sigset_t sigset;
 129         pid_t retval;
 130
 131         if (plibc_func == NULL) {
 132                 plibc_func = dlsym(RTLD_NEXT, "rfork");
 133                 if (plibc_func == NULL) {
 134                         fprintf(stderr, "libustfork: unable to find \"rfork\" symbol\n");
 135                         return -1;
 136                 }
 137         }
 138
 139         ust_before_fork(&sigset);
 140         /* Do the real rfork */
 141         retval = plibc_func();
 142         if (retval == 0) {
 143                 /* child */
 144                 ust_after_fork_child(&sigset);
 145         } else {
 146                 ust_after_fork_parent(&sigset);
 147         }
 148         return retval;
 149 }
 150
 151 /*
 152  * On BSD, no need to override vfork, because it runs in the context of
 153  * the parent, with parent waiting until execve or exit is executed in
 154  * the child.
 155  */
 156
 157 #else
 158 #warning "Unknown OS. You might want to ensure that fork/clone/vfork/fork handling is complete."
 159 #endif