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123 lines
3.4 KiB
C
123 lines
3.4 KiB
C
/*-
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* Copyright (c) 2009 Robert N. M. Watson
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* All rights reserved.
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*
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* This software was developed at the University of Cambridge Computer
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* Laboratory with support from a grant from Google, Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* When a multi-threaded application calls fork(2) from one thread while
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* another thread is blocked in accept(2), we prefer that the file descriptor
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* to be returned by accept(2) not appear in the child process. Test this by
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* creating a thread blocked in accept(2), then forking a child and seeing if
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* the fd it would have returned is defined in the child or not.
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*/
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#include <sys/socket.h>
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#include <sys/wait.h>
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#include <netinet/in.h>
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#include <err.h>
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#include <errno.h>
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#include <pthread.h>
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#include <signal.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#ifndef PORT
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#define PORT 9000
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#endif
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static int listen_fd;
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static void *
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do_accept(__unused void *arg)
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{
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int accept_fd;
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accept_fd = accept(listen_fd, NULL, NULL);
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if (accept_fd < 0)
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err(1, "accept");
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close(accept_fd);
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return (NULL);
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}
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static void
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do_fork(void)
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{
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int pid;
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pid = fork();
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if (pid < 0)
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err(1, "fork");
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if (pid > 0) {
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waitpid(pid, NULL, 0);
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exit(0);
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}
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/*
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* We will call ftruncate(2) on the next available file descriptor,
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* listen_fd+1, and get back EBADF if it's not a valid descriptor,
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* and EINVAL if it is. This (currently) works fine in practice.
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*/
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if (ftruncate(listen_fd + 1, 0) < 0) {
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if (errno == EBADF)
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exit(0);
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else if (errno == EINVAL)
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errx(1, "file descriptor still open in child");
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else
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err(1, "unexpected error");
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} else
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errx(1, "ftruncate succeeded");
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}
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int
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main(void)
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{
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struct sockaddr_in sin;
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pthread_t accept_thread;
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listen_fd = socket(PF_INET, SOCK_STREAM, 0);
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if (listen_fd < 0)
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err(1, "socket");
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bzero(&sin, sizeof(sin));
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sin.sin_family = AF_INET;
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sin.sin_len = sizeof(sin);
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sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
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sin.sin_port = htons(PORT);
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if (bind(listen_fd, (struct sockaddr *)&sin, sizeof(sin)) < 0)
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err(1, "bind");
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if (listen(listen_fd, -1) <0)
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err(1, "listen");
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if (pthread_create(&accept_thread, NULL, do_accept, NULL) != 0)
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err(1, "pthread_create");
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sleep(1); /* Easier than using a CV. */
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do_fork();
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exit(0);
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}
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