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         int saved_errno;
  37
  38         if (plibc_func == NULL) {
  39                 plibc_func = dlsym(RTLD_NEXT, "fork");
  40                 if (plibc_func == NULL) {
  41                         fprintf(stderr, "libustfork: unable to find \"fork\" symbol\n");
  42                         errno = ENOSYS;
  43                         return -1;
  44                 }
  45         }
  46
  47         ust_before_fork(&sigset);
  48         /* Do the real fork */
  49         retval = plibc_func();
  50         saved_errno = errno;
  51         if (retval == 0) {
  52                 /* child */
  53                 ust_after_fork_child(&sigset);
  54         } else {
  55                 ust_after_fork_parent(&sigset);
  56         }
  57         errno = saved_errno;
  58         return retval;
  59 }
  60
  61 int daemon(int nochdir, int noclose)
  62 {
  63         static int (*plibc_func)(int nochdir, int noclose) = NULL;
  64         sigset_t sigset;
  65         int retval;
  66         int saved_errno;
  67
  68         if (plibc_func == NULL) {
  69                 plibc_func = dlsym(RTLD_NEXT, "daemon");
  70                 if (plibc_func == NULL) {
  71                         fprintf(stderr, "libustfork: unable to find \"daemon\" symbol\n");
  72                         errno = ENOSYS;
  73                         return -1;
  74                 }
  75         }
  76
  77         ust_before_fork(&sigset);
  78         /* Do the real daemon call */
  79         retval = plibc_func(nochdir, noclose);
  80         saved_errno = errno;
  81         if (retval == 0) {
  82                 /* child, parent called _exit() directly */
  83                 ust_after_fork_child(&sigset);
  84         } else {
  85                 /* on error in the parent */
  86                 ust_after_fork_parent(&sigset);
  87         }
  88         errno = saved_errno;
  89         return retval;
  90 }
  91
  92 #ifdef __linux__
  93
  94 struct user_desc;
  95
  96 struct ustfork_clone_info {
  97         int (*fn)(void *);
  98         void *arg;
  99         sigset_t sigset;
 100 };
 101
 102 static int clone_fn(void *arg)
 103 {
 104         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
 105
 106         /* clone is now done and we are in child */
 107         ust_after_fork_child(&info->sigset);
 108         return info->fn(info->arg);
 109 }
 110
 111 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
 112 {
 113         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
 114                         int flags, void *arg, pid_t *ptid,
 115                         struct user_desc *tls, pid_t *ctid) = NULL;
 116         /* var args */
 117         pid_t *ptid;
 118         struct user_desc *tls;
 119         pid_t *ctid;
 120         /* end of var args */
 121         va_list ap;
 122         int retval;
 123         int saved_errno;
 124
 125         va_start(ap, arg);
 126         ptid = va_arg(ap, pid_t *);
 127         tls = va_arg(ap, struct user_desc *);
 128         ctid = va_arg(ap, pid_t *);
 129         va_end(ap);
 130
 131         if (plibc_func == NULL) {
 132                 plibc_func = dlsym(RTLD_NEXT, "clone");
 133                 if (plibc_func == NULL) {
 134                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
 135                         errno = ENOSYS;
 136                         return -1;
 137                 }
 138         }
 139
 140         if (flags & CLONE_VM) {
 141                 /*
 142                  * Creating a thread, no need to intervene, just pass on
 143                  * the arguments.
 144                  */
 145                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 146                                 tls, ctid);
 147                 saved_errno = errno;
 148         } else {
 149                 /* Creating a real process, we need to intervene. */
 150                 struct ustfork_clone_info info = { .fn = fn, .arg = arg };
 151
 152                 ust_before_fork(&info.sigset);
 153                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 154                                 ptid, tls, ctid);
 155                 saved_errno = errno;
 156                 /* The child doesn't get here. */
 157                 ust_after_fork_parent(&info.sigset);
 158         }
 159         errno = saved_errno;
 160         return retval;
 161 }
 162
 163 #elif defined (__FreeBSD__)
 164
 165 pid_t rfork(int flags)
 166 {
 167         static pid_t (*plibc_func)(void) = NULL;
 168         sigset_t sigset;
 169         pid_t retval;
 170         int saved_errno;
 171
 172         if (plibc_func == NULL) {
 173                 plibc_func = dlsym(RTLD_NEXT, "rfork");
 174                 if (plibc_func == NULL) {
 175                         fprintf(stderr, "libustfork: unable to find \"rfork\" symbol\n");
 176                         errno = ENOSYS;
 177                         return -1;
 178                 }
 179         }
 180
 181         ust_before_fork(&sigset);
 182         /* Do the real rfork */
 183         retval = plibc_func();
 184         saved_errno = errno;
 185         if (retval == 0) {
 186                 /* child */
 187                 ust_after_fork_child(&sigset);
 188         } else {
 189                 ust_after_fork_parent(&sigset);
 190         }
 191         errno = saved_errno;
 192         return retval;
 193 }
 194
 195 /*
 196  * On BSD, no need to override vfork, because it runs in the context of
 197  * the parent, with parent waiting until execve or exit is executed in
 198  * the child.
 199  */
 200
 201 #else
 202 #warning "Unknown OS. You might want to ensure that fork/clone/vfork/fork handling is complete."
 203 #endif