Answered: line of text and to awaken the…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

Write in C:

The default operation of xv6 console driver is to collect user keypresses into a line of text and to
awaken the processes waiting for user input only when the user presses Enter. In addition, xv6
console automatically echoes (i.e. prints out on the display) every user keypress. While this
behaviour is appropriate in many scenarios, it is not suitable for interactive gaming.
Implement ioctl() system call for the console driver that switches it into non-echoingm non-blocking
mode and test it using sample game supplied to you in user/game.c file

console.c

// Console input and output, to the uart.

// Reads are line at a time.

// Implements special input characters:

// newline -- end of line

// control-h -- backspace

// control-u -- kill line

// control-d -- end of file

// control-p -- print process list

#include <stdarg.h>

#include "types.h"

#include "param.h"

#include "spinlock.h"

#include "sleeplock.h"

#include "fs.h"

#include "file.h"

#include "memlayout.h"

#include "riscv.h"

#include "defs.h"

#include "proc.h"

#include "console.h"

#include "ioctl.h"

#define BACKSPACE 0x100

#define C(x) ((x)-'@') // Control-x

// send one character to the uart.

// called by printf(), and to echo input characters,

// but not from write().

void

consputc(int c)

{

if(c==BACKSPACE){

// if the user typed backspace, overwrite with a space.

uartputc_sync('\b'); uartputc_sync(''); uartputc_sync('\b');

} else {

uartputc_sync(c);

}

struct {

structspinlocklock;

// input

#define INPUT_BUF_SIZE 128

charbuf[INPUT_BUF_SIZE];

uintr; // Read index

uintw; // Write index

uinte; // Edit index

} cons;

// user write()s to the console go here.

int

consolewrite(int user_src, uint64 src, int n)

{

inti;

for(i=0; i<n; i++){

charc;

if(either_copyin(&c, user_src, src+i, 1) ==-1)

break;

uartputc(c);

}

returni;

}

// user read()s from the console go here.

// copy (up to) a whole input line to dst.

// user_dist indicates whether dst is a user

// or kernel address.

int

consoleread(int user_dst, uint64 dst, int n)

{

uinttarget;

intc;

charcbuf;

target=n;

acquire(&cons.lock);

while(n>0){

// wait until interrupt handler has put some

// input into cons.buffer.

while(cons.r==cons.w){

if(killed(myproc())){

release(&cons.lock);

return-1;

}

sleep(&cons.r, &cons.lock);

}

c=cons.buf[cons.r++%INPUT_BUF_SIZE];

if(c==C('D')){ // end-of-file

if(n<target){

// Save ^D for next time, to make sure

// caller gets a 0-byte result.

cons.r--;

}

break;

}

// copy the input byte to the user-space buffer.

cbuf=c;

if(either_copyout(user_dst, dst, &cbuf, 1) ==-1)

break;

dst++;

--n;

if(c=='\n'){

// a whole line has arrived, return to

// the user-level read().

break;

}

release(&cons.lock);

returntarget-n;

}

// the console input interrupt handler.

// uartintr() calls this for input character.

// do erase/kill processing, append to cons.buf,

// wake up consoleread() if a whole line has arrived.

void

consoleintr(int c)

{

acquire(&cons.lock);

switch(c){

caseC('P'): // Print process list.

procdump();

break;

caseC('U'): // Kill line.

while(cons.e!=cons.w&&

cons.buf[(cons.e-1) %INPUT_BUF_SIZE] !='\n'){

cons.e--;

consputc(BACKSPACE);

}

break;

caseC('H'): // Backspace

case'\x7f': // Delete key

if(cons.e!=cons.w){

cons.e--;

consputc(BACKSPACE);

}

break;

default:

if(c!=0&&cons.e-cons.r<INPUT_BUF_SIZE){

c= (c=='\r') ?'\n':c;

// echo back to the user.

consputc(c);

// store for consumption by consoleread().

cons.buf[cons.e++%INPUT_BUF_SIZE] =c;

if(c=='\n'||c==C('D') ||cons.e-cons.r==INPUT_BUF_SIZE){

// wake up consoleread() if a whole line (or end-of-file)

// has arrived.

cons.w=cons.e;

wakeup(&cons.r);

}

break;

}

release(&cons.lock);

}

int

consoleioctl(int user_dst, uint64 dst, int request)

{

intres=-1;

returnres;

}

void

consoleinit(void)

{

initlock(&cons.lock, "cons");

uartinit();

// connect read and write system calls

// to consoleread and consolewrite.

devsw[CONSOLE].read=consoleread;

devsw[CONSOLE].write=consolewrite;

devsw[CONSOLE].ioctl=consoleioctl;

}

---------------------------

game.c

#include "kernel/types.h"

#include "kernel/stat.h"

#include "kernel/console.h"

#include "kernel/ioctl.h"

#include "user/user.h"

#include "user/ansi.h"

#define NCOLS (80)

#define NROWS (24)

int

main(int argc, char *argv[])

{

charin=0;

intres=0;

intx=10,y=10;

intdy=0,dx=1;

/* set console into non-blocking non-echoing mode */

ioctl(0, _IO(CONSOLE_SETFL, CONSOLE_FL_NONBLOCK|CONSOLE_FL_NOECHO), 0);

ANSI_HIDE_CUR;

ANSI_CLEAR;

do {

/* !!!!!!! UNCOMMENT THE FOLLOWING LINE TO TEST YOUR ANSWER FOR Q3 !!!!!!!! */

//res = read(0,&in,1);

if (res>0) {

switch (in) {

case'w':

case'W':

dy=-1; dx=0;

break;

case'a':

case'A':

dy=0; dx=-1;

break;

case's':

case'S':

dy=1; dx=0;

break;

case'd':

case'D':

dy=0; dx=1;

break;

}

sleep(1);

ANSI_GOTOXY(x,y);

fprintf(1,"");

x=x+dx;

if( x<1 ) x=NCOLS;

if( x>NCOLS ) x=1;

y=y+dy;

if( y<1 ) y=NROWS;

if( y>NROWS ) y=1;

ANSI_GOTOXY(x,y);

fprintf(1,"@");

} while (in != '\n');

/* revert console into the normal mode of operation (blocking line-based input, echoing) */

ioctl(0, _IO(CONSOLE_SETFL,0), 0);

ANSI_RESET;

ANSI_CLEAR;

ANSI_GOTOXY(1,1);

ANSI_SHOW_CUR;

exit(0);

}

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line of text and to awaken the processes waiting for user input only when the user presses Enter. In addition, xv6 console automatically