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 TIOCLINUX

int main( int argc, char **argv )
{	
	char	bytes[ 2 ] = { 11, 0 };	// 11 is the TIOCLINUX command-number

	if ( argc == 2 ) bytes[1] = atoi( argv[1] );	// console id-number
	else	{
		fprintf( stderr, "%s: need a single argument\n", argv[0] );
		exit(1);
		}

	int	fd = open( "/dev/console", O_RDWR );		// <--- added
	if ( fd < 0 ) { perror( "/dev/console" ); exit(1); }	// <--- added
	
	if ( 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！！