liblttng-ust-fork/ustfork.c

   1 /*
   2  * Copyright (C) 2009  Pierre-Marc Fournier
   3  * Copyright (C) 2011-2012  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                         errno = ENOSYS;
  42                         return -1;
  43                 }
  44         }
  45
  46         ust_before_fork(&sigset);
  47         /* Do the real fork */
  48         retval = plibc_func();
  49         if (retval == 0) {
  50                 /* child */
  51                 ust_after_fork_child(&sigset);
  52         } else {
  53                 ust_after_fork_parent(&sigset);
  54         }
  55         return retval;
  56 }
  57
  58 #ifdef __linux__
  59
  60 struct user_desc;
  61
  62 struct ustfork_clone_info {
  63         int (*fn)(void *);
  64         void *arg;
  65         sigset_t sigset;
  66 };
  67
  68 static int clone_fn(void *arg)
  69 {
  70         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
  71
  72         /* clone is now done and we are in child */
  73         ust_after_fork_child(&info->sigset);
  74         return info->fn(info->arg);
  75 }
  76
  77 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
  78 {
  79         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
  80                         int flags, void *arg, pid_t *ptid,
  81                         struct user_desc *tls, pid_t *ctid) = NULL;
  82         /* var args */
  83         pid_t *ptid;
  84         struct user_desc *tls;
  85         pid_t *ctid;
  86         /* end of var args */
  87         va_list ap;
  88         int retval;
  89
  90         va_start(ap, arg);
  91         ptid = va_arg(ap, pid_t *);
  92         tls = va_arg(ap, struct user_desc *);
  93         ctid = va_arg(ap, pid_t *);
  94         va_end(ap);
  95
  96         if (plibc_func == NULL) {
  97                 plibc_func = dlsym(RTLD_NEXT, "clone");
  98                 if (plibc_func == NULL) {
  99                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
 100                         errno = ENOSYS;
 101                         return -1;
 102                 }
 103         }
 104
 105         if (flags & CLONE_VM) {
 106                 /*
 107                  * Creating a thread, no need to intervene, just pass on
 108                  * the arguments.
 109                  */
 110                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 111                                 tls, ctid);
 112         } else {
 113                 /* Creating a real process, we need to intervene. */
 114                 struct ustfork_clone_info info = { fn = fn, arg = arg };
 115
 116                 ust_before_fork(&info.sigset);
 117                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 118                                 ptid, tls, ctid);
 119                 /* The child doesn't get here. */
 120                 ust_after_fork_parent(&info.sigset);
 121         }
 122         return retval;
 123 }
 124
 125 #elif defined (__FreeBSD__)
 126
 127 pid_t rfork(int flags)
 128 {
 129         static pid_t (*plibc_func)(void) = NULL;
 130         sigset_t sigset;
 131         pid_t retval;
 132
 133         if (plibc_func == NULL) {
 134                 plibc_func = dlsym(RTLD_NEXT, "rfork");
 135                 if (plibc_func == NULL) {
 136                         fprintf(stderr, "libustfork: unable to find \"rfork\" symbol\n");
 137                         errno = ENOSYS;
 138                         return -1;
 139                 }
 140         }
 141
 142         ust_before_fork(&sigset);
 143         /* Do the real rfork */
 144         retval = plibc_func();
 145         if (retval == 0) {
 146                 /* child */
 147                 ust_after_fork_child(&sigset);
 148         } else {
 149                 ust_after_fork_parent(&sigset);
 150         }
 151         return retval;
 152 }
 153
 154 /*
 155  * On BSD, no need to override vfork, because it runs in the context of
 156  * the parent, with parent waiting until execve or exit is executed in
 157  * the child.
 158  */
 159
 160 #else
 161 #warning "Unknown OS. You might want to ensure that fork/clone/vfork/fork handling is complete."
 162 #endif