本次实验内容:
本实验的基本内容是修改Linux 0.11的终端设备处理代码，对键盘输入和字符显示进行非常规的控制。

在初始状态，一切如常。用户按一次F12后，把应用程序向终端输出所有字母都替换为“*”。用户再按一次F12，又恢复正常。第三次按F12，再进行输出替换。依此类推。

以ls命令为例：

正常情况：

ls
hello.c hello.o hello
第一次按F12，然后输入ls：

**
*****.* *****.* *****
第二次按F12，然后输入ls：

ls
hello.c hello.o hello
第三次按F12，然后输入ls：

**
*****.* *****.* *****

(一)修改linux-0.11/kernel/chr_drv/keyboard.S的文件

首先我们得知道 在修改之前,按下F12什么功能;
键盘I/O是典型的中断驱动，在kernel/chr_drv/console.c文件中：

void con_init(void) //控制台的初始化
{
set_trap_gate(0x21,&keyboard_interrupt); //键盘中断响应函数设为keyboard_interrupt
}
所以每次按键有动作，keyboard_interrupt函数就会被调用，它在文件kernel/chr_drv/keyboard.S

func:
    /*程序210行子函数处理功能键
      将功能键转化成转义字符存取到读队列中*/
    pushl %eax
    pushl %ecx
    pushl %edx
    call show_stat  
    popl %edx
    popl %ecx
    popl %eax

调用 show_stat 函数,显示当前 进程状态

屏蔽了 call  show_stat的功能再改成我们自己的的功能就好了
func:
    /*程序210行子函数处理功能键
      将功能键转化成转义字符存取到读队列中*/
    pushl %eax
    pushl %ecx
    pushl %edx
    //call show_stat  
    popl %edx
    popl %ecx
    popl %eax

(二)修改tty_io.c文件

linux-0.11/kernel/chr_drv/tty_io.c

键盘每次输入一个字符,操作系统都会将这个字符送到字符缓冲区进行处理.
f12是一个功能键,它的扫描码是 esc,[,[,L
分别对应ascii码的27,91,91,76
所以要连续判断四次 字符呀
你说 那我判断这几个字符的时候输出了一个其他的字符,它应该显示这个其他字符啊.
所以这段处理程序就应该写在 操作系统判断字符做出功能的代码之前.

判断字符的代码是copy_to_cooked函数

增加的全局变量
int judge=-1;
int f1=0,f2=0,f3=0;
long j=0;

void copy_to_cooked(struct tty_struct * tty)
{
    signed char c;
//now用来判断当前时间戳 
    long now;
     
    while (!EMPTY(tty->read_q) && !FULL(tty->secondary)) {
        GETCH(tty->read_q,c);
//开始添加代码
        if(c==27)
    {   
        f1=1;
        j=jiffies;
//获取当前 函数的CPU心跳数,用来计时
    }
            
        else if(f1==1&&f2==0&&c==91)
            f2=1;
        else if(f1==1&&f2==1&&c==91)
            f3=1;
        else if(f1==1&&f2==1&&f3==1&&c==76)
        {
            now=jiffies;
            if((now-j)>10)
//比如人为的输入esc,[,[,J 也会认为是F12,所以要根据四个字符的到达的时间判断是一次输入还是多次输入的~
        {
            printk("%ld \t %ld \n",j,now);
            break;
        }
            
            judge*=-1;
            continue;
        }
        else
            f1=f2=f3=0;
//添加代码结束
        if (c==13)
            if (I_CRNL(tty))
                c=10;
            else if (I_NOCR(tty))
                continue;
            else ;
        else if (c==10 && I_NLCR(tty))
            c=13;
        if (I_UCLC(tty))
            c=tolower(c);
        if (L_CANON(tty)) {
            if (c==KILL_CHAR(tty)) {
                /* deal with killing the input line */
                while(!(EMPTY(tty->secondary) ||
                        (c=LAST(tty->secondary))==10 ||
                        c==EOF_CHAR(tty))) {
                    if (L_ECHO(tty)) {
                        if (c<32)
                            PUTCH(127,tty->write_q);
                        PUTCH(127,tty->write_q);
                        tty->write(tty);
                    }
                    DEC(tty->secondary.head);
                }
                continue;
            }
            if (c==ERASE_CHAR(tty)) {
                if (EMPTY(tty->secondary) ||
                   (c=LAST(tty->secondary))==10 ||
                   c==EOF_CHAR(tty))
                    continue;
                if (L_ECHO(tty)) {
                    if (c<32)
                        PUTCH(127,tty->write_q);
                    PUTCH(127,tty->write_q);
                    tty->write(tty);
                }
                DEC(tty->secondary.head);
                continue;
            }
            if (c==STOP_CHAR(tty)) {
                tty->stopped=1;
                continue;
            }
            if (c==START_CHAR(tty)) {
                tty->stopped=0;
                continue;
            }
        }
        if (L_ISIG(tty)) {
            if (c==INTR_CHAR(tty)) {
                tty_intr(tty,INTMASK);
                continue;
            }
            if (c==QUIT_CHAR(tty)) {
                tty_intr(tty,QUITMASK);
                continue;
            }
        }
        if (c==10 || c==EOF_CHAR(tty))
            tty->secondary.data++;
        if (L_ECHO(tty)) {
            if (c==10) {
                PUTCH(10,tty->write_q);
                PUTCH(13,tty->write_q);
            } else if (c<32) {
                if (L_ECHOCTL(tty)) {
                    PUTCH('^',tty->write_q);
                    PUTCH(c+64,tty->write_q);
                }
            } else
                PUTCH(c,tty->write_q);
            tty->write(tty);
        }
        PUTCH(c,tty->secondary);
    }
    wake_up(&tty->secondary.proc_list);
}

修改后的tty_io.c文件

/*
 *  linux/kernel/tty_io.c
 *
 *  (C) 1991  Linus Torvalds
 */

/*
 * 'tty_io.c' gives an orthogonal feeling to tty's, be they consoles
 * or rs-channels. It also implements echoing, cooked mode etc.
 *
 * Kill-line thanks to John T Kohl.
 */
#include <ctype.h>
#include <errno.h>
#include <signal.h>

#define ALRMMASK (1<<(SIGALRM-1))
#define KILLMASK (1<<(SIGKILL-1))
#define INTMASK (1<<(SIGINT-1))
#define QUITMASK (1<<(SIGQUIT-1))
#define TSTPMASK (1<<(SIGTSTP-1))

#include <linux/sched.h>
#include <linux/tty.h>
#include <asm/segment.h>
#include <asm/system.h>

#define _L_FLAG(tty,f)  ((tty)->termios.c_lflag & f)
#define _I_FLAG(tty,f)  ((tty)->termios.c_iflag & f)
#define _O_FLAG(tty,f)  ((tty)->termios.c_oflag & f)

#define L_CANON(tty)    _L_FLAG((tty),ICANON)
#define L_ISIG(tty) _L_FLAG((tty),ISIG)
#define L_ECHO(tty) _L_FLAG((tty),ECHO)
#define L_ECHOE(tty)    _L_FLAG((tty),ECHOE)
#define L_ECHOK(tty)    _L_FLAG((tty),ECHOK)
#define L_ECHOCTL(tty)  _L_FLAG((tty),ECHOCTL)
#define L_ECHOKE(tty)   _L_FLAG((tty),ECHOKE)

#define I_UCLC(tty) _I_FLAG((tty),IUCLC)
#define I_NLCR(tty) _I_FLAG((tty),INLCR)
#define I_CRNL(tty) _I_FLAG((tty),ICRNL)
#define I_NOCR(tty) _I_FLAG((tty),IGNCR)

#define O_POST(tty) _O_FLAG((tty),OPOST)
#define O_NLCR(tty) _O_FLAG((tty),ONLCR)
#define O_CRNL(tty) _O_FLAG((tty),OCRNL)
#define O_NLRET(tty)    _O_FLAG((tty),ONLRET)
#define O_LCUC(tty) _O_FLAG((tty),OLCUC)
long j;
struct tty_struct tty_table[] = {
    {
        {ICRNL,     /* change incoming CR to NL */
        OPOST|ONLCR,    /* change outgoing NL to CRNL */
        0,
        ISIG | ICANON | ECHO | ECHOCTL | ECHOKE,
        0,      /* console termio */
        INIT_C_CC},
        0,          /* initial pgrp */
        0,          /* initial stopped */
        con_write,
        {0,0,0,0,""},       /* console read-queue */
        {0,0,0,0,""},       /* console write-queue */
        {0,0,0,0,""}        /* console secondary queue */
    },{
        {0, /* no translation */
        0,  /* no translation */
        B2400 | CS8,
        0,
        0,
        INIT_C_CC},
        0,
        0,
        rs_write,
        {0x3f8,0,0,0,""},       /* rs 1 */
        {0x3f8,0,0,0,""},
        {0,0,0,0,""}
    },{
        {0, /* no translation */
        0,  /* no translation */
        B2400 | CS8,
        0,
        0,
        INIT_C_CC},
        0,
        0,
        rs_write,
        {0x2f8,0,0,0,""},       /* rs 2 */
        {0x2f8,0,0,0,""},
        {0,0,0,0,""}
    }
};

/*
 * these are the tables used by the machine code handlers.
 * you can implement pseudo-tty's or something by changing
 * them. Currently not done.
 */
struct tty_queue * table_list[]={
    &tty_table[0].read_q, &tty_table[0].write_q,
    &tty_table[1].read_q, &tty_table[1].write_q,
    &tty_table[2].read_q, &tty_table[2].write_q
    };

void tty_init(void)
{
    rs_init();
    con_init();
}

void tty_intr(struct tty_struct * tty, int mask)
{
    int i;

    if (tty->pgrp <= 0)
        return;
    for (i=0;i<NR_TASKS;i++)
        if (task[i] && task[i]->pgrp==tty->pgrp)
            task[i]->signal |= mask;
}

static void sleep_if_empty(struct tty_queue * queue)
{
    cli();
    while (!current->signal && EMPTY(*queue))
        interruptible_sleep_on(&queue->proc_list);
    sti();
}

static void sleep_if_full(struct tty_queue * queue)
{
    if (!FULL(*queue))
        return;
    cli();
    while (!current->signal && LEFT(*queue)<128)
        interruptible_sleep_on(&queue->proc_list);
    sti();
}

void wait_for_keypress(void)
{
    sleep_if_empty(&tty_table[0].secondary);
}

int judge=-1;
int f1=0,f2=0,f3=0;

void copy_to_cooked(struct tty_struct * tty)
{
    signed char c;
    long now;
     
    while (!EMPTY(tty->read_q) && !FULL(tty->secondary)) {
        GETCH(tty->read_q,c);
        if(c==27)
    {   
        f1=1;
        j=jiffies;
    }
            
        else if(f1==1&&f2==0&&c==91)
            f2=1;
        else if(f1==1&&f2==1&&c==91)
            f3=1;
        else if(f1==1&&f2==1&&f3==1&&c==76)
        {
            now=jiffies;
            if((now-j)>10)
        {
            printk("%ld \t %ld \n",j,now);
            break;
        }
            
            judge*=-1;
            continue;
        }
        else
            f1=f2=f3=0;

        if (c==13)
            if (I_CRNL(tty))
                c=10;
            else if (I_NOCR(tty))
                continue;
            else ;
        else if (c==10 && I_NLCR(tty))
            c=13;
        if (I_UCLC(tty))
            c=tolower(c);
        if (L_CANON(tty)) {
            if (c==KILL_CHAR(tty)) {
                /* deal with killing the input line */
                while(!(EMPTY(tty->secondary) ||
                        (c=LAST(tty->secondary))==10 ||
                        c==EOF_CHAR(tty))) {
                    if (L_ECHO(tty)) {
                        if (c<32)
                            PUTCH(127,tty->write_q);
                        PUTCH(127,tty->write_q);
                        tty->write(tty);
                    }
                    DEC(tty->secondary.head);
                }
                continue;
            }
            if (c==ERASE_CHAR(tty)) {
                if (EMPTY(tty->secondary) ||
                   (c=LAST(tty->secondary))==10 ||
                   c==EOF_CHAR(tty))
                    continue;
                if (L_ECHO(tty)) {
                    if (c<32)
                        PUTCH(127,tty->write_q);
                    PUTCH(127,tty->write_q);
                    tty->write(tty);
                }
                DEC(tty->secondary.head);
                continue;
            }
            if (c==STOP_CHAR(tty)) {
                tty->stopped=1;
                continue;
            }
            if (c==START_CHAR(tty)) {
                tty->stopped=0;
                continue;
            }
        }
        if (L_ISIG(tty)) {
            if (c==INTR_CHAR(tty)) {
                tty_intr(tty,INTMASK);
                continue;
            }
            if (c==QUIT_CHAR(tty)) {
                tty_intr(tty,QUITMASK);
                continue;
            }
        }
        if (c==10 || c==EOF_CHAR(tty))
            tty->secondary.data++;
        if (L_ECHO(tty)) {
            if (c==10) {
                PUTCH(10,tty->write_q);
                PUTCH(13,tty->write_q);
            } else if (c<32) {
                if (L_ECHOCTL(tty)) {
                    PUTCH('^',tty->write_q);
                    PUTCH(c+64,tty->write_q);
                }
            } else
                PUTCH(c,tty->write_q);
            tty->write(tty);
        }
        PUTCH(c,tty->secondary);
    }
    wake_up(&tty->secondary.proc_list);
}

int tty_read(unsigned channel, char * buf, int nr)
{
    struct tty_struct * tty;
    char c, * b=buf;
    int minimum,time,flag=0;
    long oldalarm;

    if (channel>2 || nr<0) return -1;
    tty = &tty_table[channel];
    oldalarm = current->alarm;
    time = 10L*tty->termios.c_cc[VTIME];
    minimum = tty->termios.c_cc[VMIN];
    if (time && !minimum) {
        minimum=1;
        if ((flag=(!oldalarm || time+jiffies<oldalarm)))
            current->alarm = time+jiffies;
    }
    if (minimum>nr)
        minimum=nr;
    while (nr>0) {
        if (flag && (current->signal & ALRMMASK)) {
            current->signal &= ~ALRMMASK;
            break;
        }
        if (current->signal)
            break;
        if (EMPTY(tty->secondary) || (L_CANON(tty) &&
        !tty->secondary.data && LEFT(tty->secondary)>20)) {
            sleep_if_empty(&tty->secondary);
            continue;
        }
        do {
            GETCH(tty->secondary,c);
            if (c==EOF_CHAR(tty) || c==10)
                tty->secondary.data--;
            if (c==EOF_CHAR(tty) && L_CANON(tty))
                return (b-buf);
            else {
                put_fs_byte(c,b++);
                if (!--nr)
                    break;
            }
        } while (nr>0 && !EMPTY(tty->secondary));
        if (time && !L_CANON(tty)) {
            if ((flag=(!oldalarm || time+jiffies<oldalarm)))
                current->alarm = time+jiffies;
            else
                current->alarm = oldalarm;
        }
        if (L_CANON(tty)) {
            if (b-buf)
                break;
        } else if (b-buf >= minimum)
            break;
    }
    current->alarm = oldalarm;
    if (current->signal && !(b-buf))
        return -EINTR;
    return (b-buf);
}

int tty_write(unsigned channel, char * buf, int nr)
{
    static int cr_flag=0;
    struct tty_struct * tty;
    char c, *b=buf;

    if (channel>2 || nr<0) return -1;
    tty = channel + tty_table;
    while (nr>0) {
        sleep_if_full(&tty->write_q);
        if (current->signal)
            break;
        while (nr>0 && !FULL(tty->write_q)) {
            c=get_fs_byte(b);
            if (O_POST(tty)) {
                if (c=='\r' && O_CRNL(tty))
                    c='\n';
                else if (c=='\n' && O_NLRET(tty))
                    c='\r';
                if (c=='\n' && !cr_flag && O_NLCR(tty)) {
                    cr_flag = 1;
                    PUTCH(13,tty->write_q);
                    continue;
                }
                if (O_LCUC(tty))
                    c=toupper(c);
            }
            b++; nr--;
            cr_flag = 0;
            PUTCH(c,tty->write_q);
        }
        tty->write(tty);
        if (nr>0)
            schedule();
    }
    return (b-buf);
}

/*
 * Jeh, sometimes I really like the 386.
 * This routine is called from an interrupt,
 * and there should be absolutely no problem
 * with sleeping even in an interrupt (I hope).
 * Of course, if somebody proves me wrong, I'll
 * hate intel for all time :-). We'll have to
 * be careful and see to reinstating the interrupt
 * chips before calling this, though.
 *
 * I don't think we sleep here under normal circumstances
 * anyway, which is good, as the task sleeping might be
 * totally innocent.
 */
void do_tty_interrupt(int tty)
{
    copy_to_cooked(tty_table+tty);
}

void chr_dev_init(void)
{
}

(三)修改linux-0.11/kernel/chr_drv/console.c

tty_io.c文件只是捕捉到了按下f12的状态
我们需要在控制程序中添加 改变输出的代码,最简单的方法是只要按下F12就把所有的字符都变成"*"号输出就行了
我们只要在con_write()函数中添加一行代码:

extern int judge;//引用代码tty_io.c中的judge变量

if(judge==1)
    c='*';

con_write函数:

extern int judge;

void con_write(struct tty_struct * tty)
{
    int nr;
    char c;

    nr = CHARS(tty->write_q);
    while (nr--) {
        GETCH(tty->write_q,c);
        switch(state) {
            case 0:
                if (c>31 && c<127) {
                    if (x>=video_num_columns) {
                        x -= video_num_columns;
                        pos -= video_size_row;
                        lf();
                    }
                    if(judge==1)
                            c='*';
                    __asm__("movb attr,%%ah\n\t"
                        "movw %%ax,%1\n\t"
                        ::"a" (c),"m" (*(short *)pos)
                        );
                    pos += 2;
                    x++;
                } else if (c==27)
                    state=1;
                else if (c==10 || c==11 || c==12)
                    lf();
                else if (c==13)
                    cr();
                else if (c==ERASE_CHAR(tty))
                    del();
                else if (c==8) {
                    if (x) {
                        x--;
                        pos -= 2;
                    }
                } else if (c==9) {
                    c=8-(x&7);
                    x += c;
                    pos += c<<1;
                    if (x>video_num_columns) {
                        x -= video_num_columns;
                        pos -= video_size_row;
                        lf();
                    }
                    c=9;
                } else if (c==7)
                    sysbeep();
                break;
            case 1:
                state=0;
                if (c=='[')
                    state=2;
                else if (c=='E')
                    gotoxy(0,y+1);
                else if (c=='M')
                    ri();
                else if (c=='D')
                    lf();
                else if (c=='Z')
                    respond(tty);
                else if (x=='7')
                    save_cur();
                else if (x=='8')
                    restore_cur();
                break;
            case 2:
                for(npar=0;npar<NPAR;npar++)
                    par[npar]=0;
                npar=0;
                state=3;
                if ((ques=(c=='?')))
                    break;
            case 3:
                if (c==';' && npar<NPAR-1) {
                    npar++;
                    break;
                } else if (c>='0' && c<='9') {
                    par[npar]=10*par[npar]+c-'0';
                    break;
                } else state=4;
            case 4:
                state=0;
                switch(c) {
                    case 'G': case '`':
                        if (par[0]) par[0]--;
                        gotoxy(par[0],y);
                        break;
                    case 'A':
                        if (!par[0]) par[0]++;
                        gotoxy(x,y-par[0]);
                        break;
                    case 'B': case 'e':
                        if (!par[0]) par[0]++;
                        gotoxy(x,y+par[0]);
                        break;
                    case 'C': case 'a':
                        if (!par[0]) par[0]++;
                        gotoxy(x+par[0],y);
                        break;
                    case 'D':
                        if (!par[0]) par[0]++;
                        gotoxy(x-par[0],y);
                        break;
                    case 'E':
                        if (!par[0]) par[0]++;
                        gotoxy(0,y+par[0]);
                        break;
                    case 'F':
                        if (!par[0]) par[0]++;
                        gotoxy(0,y-par[0]);
                        break;
                    case 'd':
                        if (par[0]) par[0]--;
                        gotoxy(x,par[0]);
                        break;
                    case 'H': case 'f':
                        if (par[0]) par[0]--;
                        if (par[1]) par[1]--;
                        gotoxy(par[1],par[0]);
                        break;
                    case 'J':
                        csi_J(par[0]);
                        break;
                    case 'K':
                        csi_K(par[0]);
                        break;
                    case 'L':
                        csi_L(par[0]);
                        break;
                    case 'M':
                        csi_M(par[0]);
                        break;
                    case 'P':
                        csi_P(par[0]);
                        break;
                    case '@':
                        csi_at(par[0]);
                        break;
                    case 'm':
                        csi_m();
                        break;
                    case 'r':
                        if (par[0]) par[0]--;
                        if (!par[1]) par[1] = video_num_lines;
                        if (par[0] < par[1] &&
                            par[1] <= video_num_lines) {
                            top=par[0];
                            bottom=par[1];
                        }
                        break;
                    case 's':
                        save_cur();
                        break;
                    case 'u':
                        restore_cur();
                        break;
                }
        }
    }
    set_cursor();
}

(四)大功告成,编译运行把~

报告:

（1）在原始代码中，按下F12，中断响应后，中断服务程序会调用func？它实现的是什么功能？
将F12转义成转义字符序列 [ [ L , 对F1-F12处理类似 [ [ A -> [ [ L

（2） 在你的实现中，是否把向文件输出的字符也过滤了？如果是，那么怎么能只过滤向终端输出的字符？如果不是，那么怎么能把向文件输出的字符也一并进行过滤？

实现中并没有把向文件输出的字符也过滤，在copy_to_cooked函数处理中并不是将字符放到write_q，然后调用con_write来显示到控制台。
而是shell通过上层的sys_write系统调用将tty->secondary队列中的字符显示出来的。而在sys_write的实现过程中调用了tty_write函数。
所以只修改tty_write后，按键回显当然也变成’*’,第二次按的时候回复原来的样子;

因此要想将向文件输出的字符一并进行过滤，需要修改file_write函数。设置Flag，如果为F12按下状态，将从内核态读出的数据转为‘*’赋给用户空间即可