关于<LDD3> "setconsole.c" Alesssandro Rubini 的邮件回复

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

/* * setconsole.c -- choose a console to receive kernel messages * * Copyright (C) 1998,2000,2001 Alessandro Rubini *  *   This program is free software; you can redistribute it and/or modify *   it under the terms of the GNU General Public License as published by *   the Free Software Foundation; either version 2 of the License, or *   (at your option) any later version. * *   This program is distributed in the hope that it will be useful, *   but WITHOUT ANY WARRANTY; without even the implied warranty of *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the *   GNU General Public License for more details. * *   You should have received a copy of the GNU General Public License *   along with this program; if not, write to the Free Software *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>#include <unistd.h>#include <sys/ioctl.h>int main(int argc, char **argv){    char bytes[2] = {11,0}; /* 11 is the TIOCLINUX cmd number */    if (argc==2) bytes[1] = atoi(argv[1]); /* the chosen console */                                                                                                   else {        fprintf(stderr, "%s: need a single arg\n",argv[0]); exit(1);    }    if (ioctl(STDIN_FILENO, TIOCLINUX, bytes)<0) {    /* use stdin */        fprintf(stderr,"%s: ioctl(stdin, TIOCLINUX): %s\n",                argv[0], strerror(errno));        exit(1);    }    exit(0);}

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

//----------------------------------------------------------------//setconsole.cpp////This utility allows a user possessing root privilege //to redirect 'printk' output to a designated console. ////compile using://root# gcc -o setconsole setconsole.cpp//root# chmod a+s setconsole////execute using://user$ setconsole 4////Code used here is from an example by Alesandro Rubini,//"Linux Device Drivers (2nd Edition)," pages 99-100.//          //programmer: ALLAN CRUSE//written on: 24 NOV 2002//revised on: 24 JUN 2007 -- to use "/dev/console" device//----------------------------------------------------------------#include <fcntl.h>// for open()<--- added #include <stdio.h>// for fprintf()#include <errno.h>// for errno#include <stdlib.h>// for exit()#include <unistd.h>// for STDIN_FILENO#include <string.h>// for strerror()#include <sys/ioctl.h>// for ioctl()#include <asm/ioctls.h>// for TIOCLINUXint main( int argc, char **argv ){charbytes[ 2 ] = { 11, 0 };// 11 is the TIOCLINUX command-numberif ( argc == 2 ) bytes[1] = atoi( argv[1] );// console id-numberelse{fprintf( stderr, "%s: need a single argument\n", argv[0] );exit(1);}intfd = open( "/dev/console", O_RDWR );// <--- addedif ( fd < 0 ) { perror( "/dev/console" ); exit(1); }// <--- addedif ( ioctl( fd, TIOCLINUX, bytes ) < 0 )// <--- changed{fprintf( stderr, "%s: ioctl( fd, TIOCLINUX ): %s\n", // <--- argv[0], strerror( errno ) );exit(1);}exit(0);}

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