mit 6.1810--1.Xv6 and Unix utilities

Xv6 and Unix utilities

完成这一章花了远多于建议的时间，很大程度上是因为我对xv6内核和c语法并不熟悉，比如传实参和字符串函数。

sleep

考虑一下异常情况就行。

pingpong

关于管道：

  • read/write 的状态号对应 0/1
  • 读写结束后要及时close

find

文件有不同类型，参考 user/ls.c 的框架。

prime

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

/*
给当前数写入管道
管道中第一个数必为质数，记录并输出
用第一个数筛管道里剩下的所有数，把筛出来的加入下一个管道。
*/
void sieve(int last_read_pipe)
{
    int p, nums;
    if (read(last_read_pipe, &p, sizeof p) != sizeof p){
        close(last_read_pipe);
        return;
    }
    printf("prime %d\n", p);

    int fd[2];
    if (pipe(fd) < 0)
    {
        fprintf(2, "pipe failed\n");
        exit(1);
    }

    int pid = fork();
    if(pid < 0){
        fprintf(2, "fork failed\n");        
        exit(1);
    }

    if (pid)
    {
        close(fd[0]);
        while (read(last_read_pipe, &nums, sizeof nums) == sizeof nums)
        {
            if (nums % p)
            {
                write(fd[1], &nums, sizeof nums);
            }
        }
        close(fd[1]), close(last_read_pipe);
        wait(0);
        exit(0);
    }
    else
    {
        close(fd[1]), close(last_read_pipe);
        sieve(fd[0]);
        close(fd[0]);
        exit(0);
    }
}

int main(int argc, char *argv[])
{
    int fd[2];
    if (pipe(fd) < 0)
    {
        fprintf(2, "pipe failed\n");
        exit(1);
    }
    const int n = 35;
    for (int i = 2; i <= n; ++i){
        write(fd[1], &i, sizeof i);
    }
    close(fd[1]);
    sieve(fd[0]);
    exit(0);
}

xargs

用 malloc 动态申请内存，用 strlen\strcpy 处理字符串

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

// self real_pro pra1 pra2 ...
int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        fprintf(2, "xargs failed\n");
        exit(1);
    }

    // get stdin and attach it to the end
    const int MAX_ARG_LEN = MAXPATH;
    int argc_exev = argc - 1, index = -1;
    char c;
    char bufline[MAX_ARG_LEN];
    char *argv_exev[MAXARG];
    
    // argv[1 -> argc-1] => argv_exev
    for (int i = 1; i < argc; ++i)
    {
        argv_exev[i - 1] = (char *)malloc((strlen(argv[i]) + 1) * sizeof(char));
        strcpy(argv_exev[i - 1], argv[i]);
    }

    // read and push
    while (read(0, &c, sizeof(c)) == sizeof(c))
    {
        bufline[++index] = c;
        if (c == '\n' || c == '\0' || c == ' ')
        {           
            if(index == 0){
                index = -1;
                continue;
            }
            ++argc_exev;
            bufline[index] = '\0';
            argv_exev[argc_exev - 1] = (char *)malloc((strlen(bufline) + 1)* sizeof(char));
            strcpy(argv_exev[argc_exev - 1], bufline);
            index = -1;
        }
    }
    if(index != -1){
        ++argc_exev;
        bufline[++index] = '\0';
        argv_exev[argc_exev - 1] = (char *)malloc((strlen(bufline) + 1) * sizeof(char));
        strcpy(argv_exev[argc_exev - 1], bufline);
        index = -1;
    }
    argv_exev[argc_exev] = 0;

    // exev
    int pid = fork();
    if(pid < 0){
        fprint(2, "fork failed\n")；
        exit(1);
    }
    if (pid){
        wait(0);
    }else {
        exec(argv_exev[0], argv_exev);
    }
    exit(0);
}