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