转自 http://blog.csdn.net/cinmyheart/article/details/38960967
关于 "setconsole.c" Alesssandro Rubini 的邮件回复
抱着试一试的心态给偶像写了一封求助e-mail，回复了！！！我的小心脏啊~
呵呵~Rubini是谁不解释了...
我的HELP原文主要的关于setconsole.c的问题，这个是LDD3的一个小程序
setconsole.c
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/*
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* setconsole.c -- choose a console to receive kernel messages
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*
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* Copyright (C) 1998,2000,2001 Alessandro Rubini
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <errno.h>
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#include <unistd.h>
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#include <sys/ioctl.h>
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int main(int argc, char **argv)
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{
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char bytes[2] = {11,0}; /* 11 is the TIOCLINUX cmd number */
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if (argc==2) bytes[1] = atoi(argv[1]); /* the chosen console */
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else {
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fprintf(stderr, "%s: need a single arg\n",argv[0]); exit(1);
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}
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if (ioctl(STDIN_FILENO, TIOCLINUX, bytes)<0) { /* use stdin */
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fprintf(stderr,"%s: ioctl(stdin, TIOCLINUX): %s\n",
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argv[0], strerror(errno));
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exit(1);
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}
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exit(0);
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}
但是在虚拟控制台之间测试一直不成功，很纠结~
我用*某*搜索引擎检索了很多blog，都是水...都是直接copy原书的内容，仅发现一个有对程序进行测试的，但是测试没有成功，google不能用，不知道情况如果，用TTT检索出来的一样，没有实质性的对setconsole.c的讨论和测试！
下面是Rubini 对我的回复：
首先指出了我的误区
1. ioctl(TIOCLINUX) 影响的并不是printf，而是printk！
2.tty 或者 terminal 不是console! 通过ctrl + alt + F* (1~6 )达到的都是控制台，F7是图形环境，不是console！
Allan Cruse 在2007年对setconsole做了一点改进
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//----------------------------------------------------------------
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// setconsole.cpp
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//
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// This utility allows a user possessing root privilege
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// to redirect 'printk' output to a designated console.
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//
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// compile using:
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// root# gcc -o setconsole setconsole.cpp
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// root# chmod a+s setconsole
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//
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// execute using:
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// user$ setconsole 4
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//
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// Code used here is from an example by Alesandro Rubini,
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// "Linux Device Drivers (2nd Edition)," pages 99-100.
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//
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// programmer: ALLAN CRUSE
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// written on: 24 NOV 2002
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// revised on: 24 JUN 2007 -- to use "/dev/console" device
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//----------------------------------------------------------------
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#include <fcntl.h> // for open() <--- added
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#include <stdio.h> // for fprintf()
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#include <errno.h> // for errno
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#include <stdlib.h> // for exit()
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#include <unistd.h> // for STDIN_FILENO
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#include <string.h> // for strerror()
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#include <sys/ioctl.h> // for ioctl()
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#include <asm/ioctls.h> // for TIOCLINUX
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int main( int argc, char **argv )
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{
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char bytes[ 2 ] = { 11, 0 }; // 11 is the TIOCLINUX command-number
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if ( argc == 2 ) bytes[1] = atoi( argv[1] ); // console id-number
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else {
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fprintf( stderr, "%s: need a single argument\n", argv[0] );
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exit(1);
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}
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int fd = open( "/dev/console", O_RDWR ); // <--- added
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if ( fd < 0 ) { perror( "/dev/console" ); exit(1); } // <--- added
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if ( ioctl( fd, TIOCLINUX, bytes ) < 0 ) // <--- changed
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{
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fprintf( stderr, "%s: ioctl( fd, TIOCLINUX ): %s\n", // <---
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argv[0], strerror( errno ) );
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exit(1);
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}
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exit(0);
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}
是可以在console之间重定向IO的！！
这幅图看到的是tty4，我把控制台的IO重定向到了console 3,也就是/dev/tty3
切换到tty2，我们插入hello.ko 模块，调用printk，打印hello world
我故意执行了tty这个shell程序，提示读者当前我们在tty2,进行insmod操作
明明是有hello world的为什么不打印呢？去哪儿了？console 3!
我们ctrl + alt + F3 切换到console 3看看
终于搞定了！利用ioctl实现了对于不同console之间的IO重定向！
最后谢谢偶像~ Alesssandro Rubini & Allan Cruse
