MIT6s081

安装运行环境

sudo apt-get install git build-essential gdb-multiarch qemu-system-misc gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu sudo apt-get remove qemu-system-misc wget https://download.qemu.org/qemu-5.1.0.tar.xz tar xf qemu-5.1.0.tar.xz cd qemu-5.1.0 ./configure --disable-kvm --disable-werror --prefix=/usr/local --target-list="riscv64-softmmu" (如果缺包,放到gpt里面查询缺什么包之后安装) make

git clone git checkout -b branchname ..modify code and other git status git add . git commit -m "some comments" git push origin branchname ..request merge #after merge git push -d origin branchname #delete branch git pull origin main

labs1 website

https://pdos.csail.mit.edu/6.828/2021/labs/util.html

(1) need to configure the environment of qemu(see README.md of S0681)
(2) git clone the source code of lab1(done)
(3) make qemu and run xv6
(4) supported command in xv6

ls:list the command supported

task1:implent sleep

Implement the UNIX program sleep for xv6; your sleep should pause for a user-specified number of ticks. A tick is a notion of time defined by the xv6 kernel, namely the time between two interrupts from the timer chip. Your solution should be in the file user/sleep.c.

tips:
use command line to call the user application,the applicaiton uses the system call to implment the sleep function.

(1)user/sleep.c , include user.h,which contains the system call that can be called.

types.h:define int,short and other things.

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

int main(int argc, char *argv[])
{
  int n;
  if(argc!=2){
    fprintf(2, "Usage: sleep n...\n");
    exit(1);
  }
  n=atoi(argv[1]);
  sleep(n);
  exit(0);
}

(2) modify the makefile, like other user interface

UPROGS=\
	$U/_cat\
	$U/_echo\
	$U/_forktest\
	$U/_grep\
	$U/_init\
	$U/_kill\
	$U/_ln\
	$U/_ls\
	$U/_mkdir\
	$U/_rm\
	$U/_sh\
	$U/_stressfs\
	$U/_usertests\
	$U/_grind\
	$U/_wc\
	$U/_zombie\
	$U/_sleep\

pingpong

use pipe to create two file descriptions(use a array to store). p[0] for reading,p[1] for writing. fork create a child process.p[0]和p[1]的引用计数为2. 子进程先写后读，父进程先读后写，子进程读不到数据会在管道阻塞直到父进程向管道写入数据. 父进程类似。 所以实现的是半双工的管道通信，数据只能在一个方向流动。 如果想要实现全双工的通信，需要用两个管道。

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

int main(int argc, char *argv[]){
    int p[2];
    char buf[2];
    char *parmsg = "a";
    char *chimsg = "b";
    pipe(p);

    if (fork() == 0){
       if (read(p[0], buf, 1) != 1){
            fprintf(2, "Can't read from parent!\n");
            exit(1);
        }
        printf("child receive: %c\n", buf[0]);
        close(p[0]);
        printf("%d: received ping\n", getpid());
        if (write(p[1], chimsg, 1) != 1){
            fprintf(2, "Can't write to parent!");
        }
        close(p[1]);
        exit(0);
    }else{
        if (write(p[1], parmsg, 1) != 1){
            fprintf(2, "Can't write to child!\n");
            exit(1);
        }
        close(p[1]);
        wait(0);
        if (read(p[0], buf, 1) != 1){
            fprintf(2, "Can't read from child!");
            exit(1);
        }
        printf("parent receive: %c\n", buf[0]);
        close(p[0]);
        printf("%d: received pong\n", getpid());
        exit(0);
    }
}

find(moderate)

要求用递归方式找到指定的文件夹下符合某个名字的文件，参考user/ls.c的实现方法.

/user/find.c
void find(char *path, char *target) 

思路:递归遍历目录的所有文件，如果相等就输出文件路径，如果不相等就跳过。
(1)de中有两个结构体成员,inum是inode号,如果是0，就是非法的；name是子目录的名字.
如.目录下子目录的名字: .
..
README
xargstest.sh
cat
echo
(.......)
.表示当前目录，..表示上一级目录，遍历的时候需要跳过。

(2) int stat(const char*, struct stat*); 表示获取路径的相关信息.

             stat结构体
             struct stat {
                 int dev;     // File system's disk device
                 uint ino;    // Inode number
                 short type;  // Type of file
                 short nlink; // Number of links to file
                 uint64 size; // Size of file in bytes
             }
             inode号，链接数，文件类型

使用buf接受目录,然后使用read读取子目录的de结构体，拼接到buf后面，然后使用stat获取相关信息，如果是目录，就递归访问;
如果是文件，就把子目录的名字 和 目标文件进行对比,如果相等就输出。