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 <lttng/ust-dlfcn.h>
  22 #include <unistd.h>
  23 #include <stdio.h>
  24 #include <signal.h>
  25 #include <sched.h>
  26 #include <stdarg.h>
  27 #include <errno.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 int daemon(int nochdir, int noclose)
  59 {
  60         static int (*plibc_func)(int nochdir, int noclose) = NULL;
  61         sigset_t sigset;
  62         int retval;
  63
  64         if (plibc_func == NULL) {
  65                 plibc_func = dlsym(RTLD_NEXT, "daemon");
  66                 if (plibc_func == NULL) {
  67                         fprintf(stderr, "libustfork: unable to find \"daemon\" symbol\n");
  68                         errno = ENOSYS;
  69                         return -1;
  70                 }
  71         }
  72
  73         ust_before_fork(&sigset);
  74         /* Do the real daemon call */
  75         retval = plibc_func(nochdir, noclose);
  76         if (retval == 0) {
  77                 /* child, parent called _exit() directly */
  78                 ust_after_fork_child(&sigset);
  79         } else {
  80                 /* on error in the parent */
  81                 ust_after_fork_parent(&sigset);
  82         }
  83         return retval;
  84 }
  85
  86 #ifdef __linux__
  87
  88 struct user_desc;
  89
  90 struct ustfork_clone_info {
  91         int (*fn)(void *);
  92         void *arg;
  93         sigset_t sigset;
  94 };
  95
  96 static int clone_fn(void *arg)
  97 {
  98         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
  99
 100         /* clone is now done and we are in child */
 101         ust_after_fork_child(&info->sigset);
 102         return info->fn(info->arg);
 103 }
 104
 105 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
 106 {
 107         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
 108                         int flags, void *arg, pid_t *ptid,
 109                         struct user_desc *tls, pid_t *ctid) = NULL;
 110         /* var args */
 111         pid_t *ptid;
 112         struct user_desc *tls;
 113         pid_t *ctid;
 114         /* end of var args */
 115         va_list ap;
 116         int retval;
 117
 118         va_start(ap, arg);
 119         ptid = va_arg(ap, pid_t *);
 120         tls = va_arg(ap, struct user_desc *);
 121         ctid = va_arg(ap, pid_t *);
 122         va_end(ap);
 123
 124         if (plibc_func == NULL) {
 125                 plibc_func = dlsym(RTLD_NEXT, "clone");
 126                 if (plibc_func == NULL) {
 127                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
 128                         errno = ENOSYS;
 129                         return -1;
 130                 }
 131         }
 132
 133         if (flags & CLONE_VM) {
 134                 /*
 135                  * Creating a thread, no need to intervene, just pass on
 136                  * the arguments.
 137                  */
 138                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 139                                 tls, ctid);
 140         } else {
 141                 /* Creating a real process, we need to intervene. */
 142                 struct ustfork_clone_info info = { .fn = fn, .arg = arg };
 143
 144                 ust_before_fork(&info.sigset);
 145                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 146                                 ptid, tls, ctid);
 147                 /* The child doesn't get here. */
 148                 ust_after_fork_parent(&info.sigset);
 149         }
 150         return retval;
 151 }
 152
 153 #elif defined (__FreeBSD__)
 154
 155 pid_t rfork(int flags)
 156 {
 157         static pid_t (*plibc_func)(void) = NULL;
 158         sigset_t sigset;
 159         pid_t retval;
 160
 161         if (plibc_func == NULL) {
 162                 plibc_func = dlsym(RTLD_NEXT, "rfork");
 163                 if (plibc_func == NULL) {
 164                         fprintf(stderr, "libustfork: unable to find \"rfork\" symbol\n");
 165                         errno = ENOSYS;
 166                         return -1;
 167                 }
 168         }
 169
 170         ust_before_fork(&sigset);
 171         /* Do the real rfork */
 172         retval = plibc_func();
 173         if (retval == 0) {
 174                 /* child */
 175                 ust_after_fork_child(&sigset);
 176         } else {
 177                 ust_after_fork_parent(&sigset);
 178         }
 179         return retval;
 180 }
 181
 182 /*
 183  * On BSD, no need to override vfork, because it runs in the context of
 184  * the parent, with parent waiting until execve or exit is executed in
 185  * the child.
 186  */
 187
 188 #else
 189 #warning "Unknown OS. You might want to ensure that fork/clone/vfork/fork handling is complete."
 190 #endif