MIT 6.S081---Lab util: Unix utilities

环境搭建

基本环境

选择的是Vmware+ubuntu的配置，注意ubuntu的版本一定要是20.04，作者试过16版本，不行，建议直接安装20.04版，不然环境配置都浪费不少时间有点得不偿失。（Vmware可以用Virtualbox代替）

qemu+xv6

参考官网教程
ps：刚装好的系统可以先更换镜像源（参考ubuntu 20.04 LTS 更换阿里云源）
这里将官网教程流程拷贝下来供大家拷贝：
第一步：

sudo apt-get install git build-essential gdb-multiarch qemu-system-misc gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu 

第二步：

sudo apt-get remove qemu-system-misc
sudo apt-get install qemu-system-misc=1:4.2-3ubuntu6

测试结果如下显示就是对的：

# in the xv6 directory
make qemu
# ... lots of output ...
init: starting sh
$

gitee配置

本处采用git来协调不同平台的代码，由于gitub比较慢于是将代码上传到gitee上（上传的时候可能会显示冲突，解决方法参考：代码冲突强制覆盖上传）,至于gitee如何配置环境可以参考Windows环境安装及配置git并连接gitee远程仓库和ubuntu下Git的安装和使用（针对gitee）
。

实验部分

sleep (easy)

实现一个简单的休眠函数，容易，调api即可

//sleep.c
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"


int main(int argc, char *argv[]) {
    // int i;
    if (argc == 2) {
        sleep(atoi(argv[1]));
    } else {
        fprintf(2, "there is a need for an augument to determin the time to sleep");
        exit(1);
    }
    exit(0);
}

pingpong (easy)

考察到了pipe()函数的使用，使用管道一端写一端读即可。

//pingpong.c
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"

char buf[96];

char tmp[100];

char* itoch(int input) {
    int i = 0;
    int l, r;
    while (input != 0) {
        tmp[i++] = (input % 10) + '0';
        input /= 10;
    }
    l = 0;
    r = i - 1;
    while (l < r) {
        char temp = tmp[l];
        tmp[l] = tmp[r];
        tmp[r] = temp;
        l++;
        r--;
    }
    tmp[i] = '\0';
    // fprintf(1, tmp);
    return tmp;
}

int main(int argc, char *argv[]) {
    int pftos[2], pstof[2];
    pipe(pftos);
    pipe(pstof);
    // int pid = fork();
    // read
    // getpid
    if (fork() == 0) {
        //son pid
        close(pftos[1]);
        close(pstof[0]);
        // fprintf(1, "son read\n");
        if (read(pftos[0], buf, sizeof(buf)) != 1) {
            fprintf(2, "ping read error");
            exit(1);
        }
        // fprintf(1, "son read success\n");
        char* tmp = itoch(getpid());
        fprintf(1, tmp);
        fprintf(1, ": ");
        fprintf(1, "received ping\n");

        if (write(pstof[1], "i", 1) != 1) {
            fprintf(2, "pong write error");
            exit(1);
        }
        close(pftos[0]);
        close(pstof[1]);
        exit(0);
    }
    //parent pid
    close(pftos[0]);
    close(pstof[1]);
    // fprintf(1, "father write begin\n");
    if (write(pftos[1], "o", 1) != 1) {
        fprintf(2, "ping write error");
        exit(1);
    }
    // fprintf(1, "father write success\n");

    if (read(pstof[0], buf, sizeof(buf)) != 1) {
        fprintf(2, "pong read error");
        exit(1);
    }
    char* tmp = itoch(getpid());
    fprintf(1, tmp);
    fprintf(1, ": ");
    fprintf(1, "received pong\n");
    wait(0);
    close(pftos[1]);
    close(pstof[0]);
    exit(0);
}

primes (moderate)/(hard)

通过筛子来筛选，具体如下图所示：

需要注意两点：

1. 注意文件描述符的关闭，如果不及时关闭描述符可能会用尽文件描述符；
2. 注意关闭管道的写端，当管道的写端的引用为0时read读端才会返回零，代表文件结束。
   本处的代码并没有优化到最好，个人认为更好的实现可参考：6.S081-Lab1 总结笔记（0基础向）
   

#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/spinlock.h"


typedef enum {
    true = 1,
    false = 0
} bool;

void buildProcess(int listenfd, int writefd) {
    int num;
    int self = -1;
    int status = fork();
    if (status == 0) {
        bool next = false;
        close(writefd);
        close(0);
        dup(listenfd);
        close(listenfd);
        //close(1);
        //dup(pfd[1]);
        //close(pfd[1]);
        int pfd[2];
        pipe(pfd);
        while (1) {
            int read_bytes = read(0, &num, 4);
            if (read_bytes == 0 || read_bytes == -1) {
                break;
            }
            if (self == -1) {
                self = num;
                printf("prime %d\n", num);
                continue;
            }
            
            if (num % self != 0) {
                if (!next) {
                    next = true;
                    buildProcess(pfd[0], pfd[1]);
                }
                write(pfd[1], &num, 4); 
            }
        } 
        close(pfd[0]);
        close(pfd[1]);
        close(0);
        wait(0);
        exit(0);
    } else if (status == -1) {
        fprintf(2, "fork error");
        exit(1);
    } 
    
}

int main(int argc, char* argv[]) {
    int i;
    bool next = false;
    int pfd[2];
    pipe(pfd);
    for (i = 2; i <= 35; ++i) {
        if (i == 2) {
            printf("prime %d\n", i);
        }
        if (i % 2 == 1) {
            if (!next) {
                next = true;
                buildProcess(pfd[0], pfd[1]);
                close(pfd[0]);
            }
            write(pfd[1], &i, 4);
        } 
    }
    close(pfd[1]);
    printf("end");
    wait(0);
    exit(0);
}

注释：有个待解决的问题，就是pipe后的两个文件描述符中，似乎不能将写端重定向到文件描述符1，具体原因待阅读源码后确认。

find (moderate)

这题算比较简单了，注意参考usr/find.c

#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/fs.h"

void find(const char* root, const char* target) {
    char buf[512], *p;
    int fd;
    struct dirent de;
    struct stat st;

    if((fd = open(root, 0)) < 0){
        fprintf(2, "find: cannot open %s\n", root);
        return;
    }

    if(fstat(fd, &st) < 0){
        fprintf(2, "find: cannot stat %s\n", root);
        close(fd);
        return;
    }

    if (st.type == T_FILE) {
        fprintf(2, "%s is no a directory!!!\n", root);
        close(fd);
        return;
    }

    if(strlen(root) + 1 + DIRSIZ + 1 > sizeof buf){
        printf("ls: path too long\n");
    }
    strcpy(buf, root);
    p = buf+strlen(buf);
    *p++ = '/';
    while(read(fd, &de, sizeof(de)) == sizeof(de)){
        if(de.inum == 0 || strcmp(de.name, ".") == 0 || strcmp(de.name, "..") == 0) continue;
        strcpy(p, de.name);
        int tmpfd;
        if((tmpfd = open(buf, 0)) < 0){
            fprintf(2, "open: cannot open %s\n", buf);
            return;
        }
        if(fstat(tmpfd, &st) < 0){
            fprintf(2, "fstat: cannot stat %s\n", buf);
            close(tmpfd);
            return;
        }
        if (st.type == T_FILE) {
            if (strcmp(de.name, target) == 0) {
                printf("%s/", root);
                printf("%s\n", de.name);
            }
        } else if (st.type == T_DIR) {
            find(buf, target);
        }
        close(tmpfd);
    }
    close(fd);
}

int main(int argc, char* argv[]) {
    if (argc != 3) {
        fprintf(2, "too many or too few parameters\n");
        exit(1);
    }
    find(argv[1], argv[2]);
    exit(0);
}

xargs (moderate)

注意exec的参数，别的话就是些细节啦

#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"

char buf[1024];

int main(int argc, char* argv[]) {
    int i;
    int line = 0;
    int size = read(0, buf, sizeof buf);
    char* input[argc];
    for (i = 1; i < argc; ++i) {
        input[i - 1] = argv[i];
    }
    if (size == -1) {
        fprintf(2, "read error");
    }

    for (i = 0; i < size; i++) {
        if (buf[i] == '\n') {
            line++;
        }
    }
    char arguments[line][32];
    int pos = 0, curr = 0;
    for (i = 0; i < size; ++i) {
        if (buf[i] == '\n') {
            arguments[curr][pos] = '\0';
            curr++;
            pos = 0;
        } else {
            arguments[curr][pos++] = buf[i];
        }
    }
    for (i = 0; i < line; ++i) {
        input[argc - 1] = arguments[i];
        if (fork() == 0) {
            exec(argv[1], input);
            exit(0);
        }
        wait(0);
    }
    exit(0);
}