1188483Srwatson/*- 2188483Srwatson * Copyright (c) 2009 Robert N. M. Watson 3188483Srwatson * All rights reserved. 4188483Srwatson * 5188483Srwatson * This software was developed at the University of Cambridge Computer 6188483Srwatson * Laboratory with support from a grant from Google, Inc. 7188483Srwatson * 8188483Srwatson * Redistribution and use in source and binary forms, with or without 9188483Srwatson * modification, are permitted provided that the following conditions 10188483Srwatson * are met: 11188483Srwatson * 1. Redistributions of source code must retain the above copyright 12188483Srwatson * notice, this list of conditions and the following disclaimer. 13188483Srwatson * 2. Redistributions in binary form must reproduce the above copyright 14188483Srwatson * notice, this list of conditions and the following disclaimer in the 15188483Srwatson * documentation and/or other materials provided with the distribution. 16188483Srwatson * 17188483Srwatson * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18188483Srwatson * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19188483Srwatson * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20188483Srwatson * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21188483Srwatson * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22188483Srwatson * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23188483Srwatson * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24188483Srwatson * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25188483Srwatson * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26188483Srwatson * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27188483Srwatson * SUCH DAMAGE. 28188483Srwatson * 29188483Srwatson * $FreeBSD$ 30188483Srwatson */ 31188483Srwatson 32188483Srwatson/* 33188483Srwatson * When a multi-threaded application calls fork(2) from one thread while 34188483Srwatson * another thread is blocked in accept(2), we prefer that the file descriptor 35188483Srwatson * to be returned by accept(2) not appear in the child process. Test this by 36188483Srwatson * creating a thread blocked in accept(2), then forking a child and seeing if 37188483Srwatson * the fd it would have returned is defined in the child or not. 38188483Srwatson */ 39188483Srwatson 40188483Srwatson#include <sys/socket.h> 41188483Srwatson#include <sys/wait.h> 42188483Srwatson 43188483Srwatson#include <netinet/in.h> 44188483Srwatson 45188483Srwatson#include <err.h> 46188483Srwatson#include <errno.h> 47188483Srwatson#include <pthread.h> 48188483Srwatson#include <signal.h> 49188483Srwatson#include <stdlib.h> 50188483Srwatson#include <string.h> 51188483Srwatson#include <unistd.h> 52188483Srwatson 53188483Srwatson#define PORT 9000 54188483Srwatson 55188483Srwatsonstatic int listen_fd; 56188483Srwatson 57188483Srwatsonstatic void * 58188483Srwatsondo_accept(__unused void *arg) 59188483Srwatson{ 60188483Srwatson int accept_fd; 61188483Srwatson 62188483Srwatson accept_fd = accept(listen_fd, NULL, NULL); 63188483Srwatson if (accept_fd < 0) 64188483Srwatson err(-1, "accept"); 65188483Srwatson 66188483Srwatson return (NULL); 67188483Srwatson} 68188483Srwatson 69188483Srwatsonstatic void 70188483Srwatsondo_fork(void) 71188483Srwatson{ 72188483Srwatson int pid; 73188483Srwatson 74188483Srwatson pid = fork(); 75188483Srwatson if (pid < 0) 76188483Srwatson err(-1, "fork"); 77188483Srwatson if (pid > 0) { 78188483Srwatson waitpid(pid, NULL, 0); 79188483Srwatson exit(0); 80188483Srwatson } 81188483Srwatson 82188483Srwatson /* 83188483Srwatson * We will call ftruncate(2) on the next available file descriptor, 84188483Srwatson * listen_fd+1, and get back EBADF if it's not a valid descriptor, 85188483Srwatson * and EINVAL if it is. This (currently) works fine in practice. 86188483Srwatson */ 87188483Srwatson if (ftruncate(listen_fd + 1, 0 < 0)) { 88188483Srwatson if (errno == EBADF) 89188483Srwatson exit(0); 90188483Srwatson else if (errno == EINVAL) 91188483Srwatson errx(-1, "file descriptor still open in child"); 92188483Srwatson else 93188483Srwatson err(-1, "unexpected error"); 94188483Srwatson } else 95188483Srwatson errx(-1, "ftruncate succeeded"); 96188483Srwatson} 97188483Srwatson 98188483Srwatsonint 99188483Srwatsonmain(__unused int argc, __unused char *argv[]) 100188483Srwatson{ 101188483Srwatson struct sockaddr_in sin; 102188483Srwatson pthread_t accept_thread; 103188483Srwatson 104188483Srwatson listen_fd = socket(PF_INET, SOCK_STREAM, 0); 105188483Srwatson if (listen_fd < 0) 106188483Srwatson err(-1, "socket"); 107188483Srwatson bzero(&sin, sizeof(sin)); 108188483Srwatson sin.sin_family = AF_INET; 109188483Srwatson sin.sin_len = sizeof(sin); 110188483Srwatson sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK); 111188483Srwatson sin.sin_port = htons(PORT); 112188483Srwatson if (bind(listen_fd, (struct sockaddr *)&sin, sizeof(sin)) < 0) 113188483Srwatson err(-1, "bind"); 114188483Srwatson if (listen(listen_fd, -1) <0) 115188483Srwatson err(-1, "listen"); 116203800Sru if (pthread_create(&accept_thread, NULL, do_accept, NULL) != 0) 117188483Srwatson err(-1, "pthread_create"); 118188483Srwatson sleep(1); /* Easier than using a CV. */; 119188483Srwatson do_fork(); 120188483Srwatson exit(0); 121188483Srwatson} 122