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 struct user_desc;
  32
  33 pid_t fork(void)
  34 {
  35         static pid_t (*plibc_func)(void) = NULL;
  36         sigset_t sigset;
  37         pid_t retval;
  38
  39         if (plibc_func == NULL) {
  40                 plibc_func = dlsym(RTLD_NEXT, "fork");
  41                 if (plibc_func == NULL) {
  42                         fprintf(stderr, "libustfork: unable to find \"fork\" symbol\n");
  43                         return -1;
  44                 }
  45         }
  46
  47         ust_before_fork(&sigset);
  48         /* Do the real fork */
  49         retval = plibc_func();
  50         if (retval == 0) {
  51                 /* child */
  52                 ust_after_fork_child(&sigset);
  53         } else {
  54                 ust_after_fork_parent(&sigset);
  55         }
  56         return retval;
  57 }
  58
  59 int daemon(int nochdir, int noclose)
  60 {
  61         static int (*plibc_func)(int nochdir, int noclose) = NULL;
  62         sigset_t sigset;
  63         int retval;
  64
  65         if (plibc_func == NULL) {
  66                 plibc_func = dlsym(RTLD_NEXT, "daemon");
  67                 if (plibc_func == NULL) {
  68                         fprintf(stderr, "libustfork: unable to find \"daemon\" symbol\n");
  69                         errno = ENOSYS;
  70                         return -1;
  71                 }
  72         }
  73
  74         ust_before_fork(&sigset);
  75         /* Do the real daemon call */
  76         retval = plibc_func(nochdir, noclose);
  77         if (retval == 0) {
  78                 /* child, parent called _exit() directly */
  79                 ust_after_fork_child(&sigset);
  80         } else {
  81                 /* on error in the parent */
  82                 ust_after_fork_parent(&sigset);
  83         }
  84         return retval;
  85 }
  86
  87 struct ustfork_clone_info {
  88         int (*fn)(void *);
  89         void *arg;
  90         sigset_t sigset;
  91 };
  92
  93 static int clone_fn(void *arg)
  94 {
  95         struct ustfork_clone_info *info = (struct ustfork_clone_info *) arg;
  96
  97         /* clone is now done and we are in child */
  98         ust_after_fork_child(&info->sigset);
  99         return info->fn(info->arg);
 100 }
 101
 102 int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
 103 {
 104         static int (*plibc_func)(int (*fn)(void *), void *child_stack,
 105                         int flags, void *arg, pid_t *ptid,
 106                         struct user_desc *tls, pid_t *ctid) = NULL;
 107         /* var args */
 108         pid_t *ptid;
 109         struct user_desc *tls;
 110         pid_t *ctid;
 111         /* end of var args */
 112         va_list ap;
 113         int retval;
 114
 115         va_start(ap, arg);
 116         ptid = va_arg(ap, pid_t *);
 117         tls = va_arg(ap, struct user_desc *);
 118         ctid = va_arg(ap, pid_t *);
 119         va_end(ap);
 120
 121         if (plibc_func == NULL) {
 122                 plibc_func = dlsym(RTLD_NEXT, "clone");
 123                 if (plibc_func == NULL) {
 124                         fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
 125                         return -1;
 126                 }
 127         }
 128
 129         if (flags & CLONE_VM) {
 130                 /*
 131                  * Creating a thread, no need to intervene, just pass on
 132                  * the arguments.
 133                  */
 134                 retval = plibc_func(fn, child_stack, flags, arg, ptid,
 135                                 tls, ctid);
 136         } else {
 137                 /* Creating a real process, we need to intervene. */
 138                 struct ustfork_clone_info info = { .fn = fn, .arg = arg };
 139
 140                 ust_before_fork(&info.sigset);
 141                 retval = plibc_func(clone_fn, child_stack, flags, &info,
 142                                 ptid, tls, ctid);
 143                 /* The child doesn't get here. */
 144                 ust_after_fork_parent(&info.sigset);
 145         }
 146         return retval;
 147 }