1 /*- 2 * Copyright (c) 2009 Robert N. M. Watson 3 * All rights reserved. 4 * 5 * This software was developed at the University of Cambridge Computer 6 * Laboratory with support from a grant from Google, Inc. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 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 * 29 * $FreeBSD$ 30 */ 31 32 /* 33 * When a multi-threaded application calls fork(2) from one thread while 34 * another thread is blocked in accept(2), we prefer that the file descriptor 35 * to be returned by accept(2) not appear in the child process. Test this by 36 * creating a thread blocked in accept(2), then forking a child and seeing if 37 * the fd it would have returned is defined in the child or not. 38 */ 39 40 #include <sys/socket.h> 41 #include <sys/wait.h> 42 43 #include <netinet/in.h> 44 45 #include <err.h> 46 #include <errno.h> 47 #include <pthread.h> 48 #include <signal.h> 49 #include <stdlib.h> 50 #include <string.h> 51 #include <unistd.h> 52 53 #define PORT 9000 54 55 static int listen_fd; 56 57 static void * 58 do_accept(__unused void *arg) 59 { 60 int accept_fd; 61 62 accept_fd = accept(listen_fd, NULL, NULL); 63 if (accept_fd < 0) 64 err(1, "accept"); 65 66 close(accept_fd); 67 return (NULL); 68 } 69 70 static void 71 do_fork(void) 72 { 73 int pid; 74 75 pid = fork(); 76 if (pid < 0) 77 err(1, "fork"); 78 if (pid > 0) { 79 waitpid(pid, NULL, 0); 80 exit(0); 81 } 82 83 /* 84 * We will call ftruncate(2) on the next available file descriptor, 85 * listen_fd+1, and get back EBADF if it's not a valid descriptor, 86 * and EINVAL if it is. This (currently) works fine in practice. 87 */ 88 if (ftruncate(listen_fd + 1, 0) < 0) { 89 if (errno == EBADF) 90 exit(0); 91 else if (errno == EINVAL) 92 errx(1, "file descriptor still open in child"); 93 else 94 err(1, "unexpected error"); 95 } else 96 errx(1, "ftruncate succeeded"); 97 } 98 99 int 100 main(void) 101 { 102 struct sockaddr_in sin; 103 pthread_t accept_thread; 104 105 listen_fd = socket(PF_INET, SOCK_STREAM, 0); 106 if (listen_fd < 0) 107 err(1, "socket"); 108 bzero(&sin, sizeof(sin)); 109 sin.sin_family = AF_INET; 110 sin.sin_len = sizeof(sin); 111 sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK); 112 sin.sin_port = htons(PORT); 113 if (bind(listen_fd, (struct sockaddr *)&sin, sizeof(sin)) < 0) 114 err(1, "bind"); 115 if (listen(listen_fd, -1) <0) 116 err(1, "listen"); 117 if (pthread_create(&accept_thread, NULL, do_accept, NULL) != 0) 118 err(1, "pthread_create"); 119 sleep(1); /* Easier than using a CV. */ 120 do_fork(); 121 exit(0); 122 } 123