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root/usr/lib/posix/process/fork.c

DEFINITIONS

1. fork
2. __child_entry
3. vfork

   1 /*
   2  * Copyright (c) 2005-2006, Kohsuke Ohtani
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the author nor the names of any co-contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  30 #include <sys/prex.h>
  31 #include <sys/posix.h>
  32 #include <sys/signal.h>
  33 #include <ipc/proc.h>
  34 #include <ipc/fs.h>
  35 #include <ipc/ipc.h>
  37 #include <stddef.h>
  38 #include <setjmp.h>
  39 #include <errno.h>
  40 #include <unistd.h>
  42 static void __child_entry(void);
  44 static jmp_buf __fork_env;
  46 /*
  47  * fork() - fork for MMU system.
  48  *
  49  * RETURN VALUE:
  50  *
  51  *  fork() returns 0 to the child process and return the process
  52  *  ID of the child process to the parent process. Or, -1 will be
  53  *  returned to the parent process if error.
  54  *
  55  * ERRORS:
  56  *
  57  *  EAGAIN
  58  *  ENOMEM
  59  *
  60  * NOTE:
  61  *
  62  *  Since no thread is created by task_create(), thread_create()
  63  *  must be called follwing task_crate(). But, when new thread is
  64  *  created by thread_create(), the stack pointer of new thread is
  65  *  used at thread_create() although the stack image is copied at
  66  *  task_create(). So, the stack pointer must be reset to same
  67  *  address of thread_create() before calling task_create();
  68  *  This is a little tricky...
  69  *
  70  * The new process is an exact copy of the calling process
  71  * except as detailed below:
  72  * - Process IDs are different.
  73  * - tms_* is set to 0.
  74  * - Alarm clock is set to 0.
  75  * - Opend semaphore is inherited.
  76  * - Pending signals are cleared.
  77  *
  78  * - File lock is not inherited.
  79  * - File descriptor is shared.
  80  * - Directory stream is shared.
  81  */
  82 static pid_t
fork(void)
  84 {
  85         struct msg m;
task_t tsk;
thread_t t;
  88         int error;
pid_t pid;
  91         /* Save current stack pointer */
  92         if (setjmp(__fork_env) == 0) {
  93                 /*
  94                  * Create new task
  95                  */
error = task_create(task_self(), VM_COPY, &tsk);
  97                 if (error) {
errno = error;
  99                         return -1;
 100                 }
 101                 if ((error = thread_create(tsk, &t)) != 0) {
task_terminate(tsk);
errno = error;
 104                         return -1;
 105                 }
 106                 /*
 107                  * Notify to process server
 108                  */
m.hdr.code = PS_FORK;
m.data[0] = tsk;                /* child task */
m.data[1] = 0;                  /* fork type */
 112                 if (__posix_call(__proc_obj, &m, sizeof(m), 1) != 0)
 113                         return -1;
pid = m.data[0];
 116                 /*
 117                  * Notify to file system server
 118                  */
m.hdr.code = FS_FORK;
m.data[0] = tsk;                /* child task */
 121                 if (__posix_call(__fs_obj, &m, sizeof(m), 1) != 0)
 122                         return -1;
 124                 /*
 125                  * Start child task
 126                  */
thread_load(t, __child_entry, NULL);
thread_resume(t);
 129         } else {
 130                 /*
 131                  * Child task
 132                  */
 133 #ifdef _REENTRANT
error = mutex_init(&__sig_lock);
 135 #endif
__sig_pending = 0;
 137                 return 0;
 138         }
 139         return pid;
 140 }
 142 static void
__child_entry(void)
 144 {
longjmp(__fork_env, 1);
 147         /* NOTREACHED */
 148 }
pid_t
vfork(void)
 152 {
 154         return fork();
 155 }