@author : FlyingPig
@email : [email protected]
第一个lab相对容易，主要是让大家熟悉xv6和系统调用。
从仓库clone代码，配置好环境后，在命令行运行
make qemu即可启动xv6操作系统。
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
int
main(int argc, char const *argv[])
{
if (argc != 2)
{
fprintf(2, "Usage: sleep seconds\n");
exit(1);
}
int time = atoi(argv[1]);
sleep(time);
exit(0);
}直接调用sleep系统调用即可。
这个lab主要是利用pipe系统调用来实现两个进程间的通信，需要注意的是记得close不需要的文件描述符。
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
int main(int argc, char const *argv[])
{
int pid;
int p[2];
pipe(p);
if (fork() == 0) // child (receive -> send)
{
pid = getpid();
char buf[2];
if (read(p[0], buf, 1) != 1)
{
fprintf(2, "failed to read in child\n");
exit(1);
}
close(p[0]);
printf("%d: received ping\n", pid);
if(write(p[1], buf, 1) != 1)
{
fprintf(2, "failed to write in child\n");
exit(1);
}
close(p[1]);
exit(0);
}else{ // parent (send -> receive)
pid = getpid();
char info[2] = "a";
char buf[2];
buf[1] = 0;
if (write(p[1], info, 1) != 1)
{
fprintf(2, "failed to write in parent\n");
exit(1);
}
// wait for child to receive ping
close(p[1]);
wait(0);
if(read(p[0], buf, 1) != 1){
fprintf(2, "failed to read in parent\n");
exit(1);
}
printf("%d: received pong\n", pid);
close(p[0]);
exit(0);
}
}这个lab主要利用了pipe和fork系统调用实现了一个并行化的素数筛。
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
void new_proc(int p[2]){
int prime;
int flag;
int n;
close(p[1]);
if(read(p[0], &prime, 4) != 4){
fprintf(2, "child process failed to read\n");
exit(1);
}
printf("prime %d\n", prime);
flag = read(p[0], &n, 4);
if(flag){
int newp[2];
pipe(newp);
if (fork() == 0)
{
new_proc(newp);
}else
{
close(newp[0]);
if(n%prime)write(newp[1], &n, 4);
while(read(p[0], &n, 4)){
if(n%prime)write(newp[1], &n, 4);
}
close(p[0]);
close(newp[1]);
wait(0);
}
}
exit(0);
}
int main(int argc, char const *argv[])
{
int p[2];
pipe(p);
if (fork() == 0)
{
new_proc(p);
}else
{
close(p[0]);
for(int i = 2; i <= 35; i++)
{
if (write(p[1], &i, 4) != 4)
{
fprintf(2, "first process failed to write %d into the pipe\n", i);
exit(1);
}
}
close(p[1]);
wait(0);
exit(0);
}
return 0;
}利用文件系统调用实现一个简单的find函数。
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/fs.h"
void find_helper(char const *path, char const *target)
{
char buf[512], *p;
int fd;
struct dirent de;
struct stat st;
if((fd = open(path, 0)) < 0){
fprintf(2, "find: cannot open %s\n", path);
exit(1);
}
if(fstat(fd, &st) < 0){
fprintf(2, "find: cannot stat %s\n", path);
exit(1);
}
switch(st.type){
case T_FILE:
fprintf(2, "Usage: find dir file\n");
exit(1);
case T_DIR:
if(strlen(path) + 1 + DIRSIZ + 1 > sizeof buf){
printf("find: path too long\n");
break;
}
strcpy(buf, path);
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;
memmove(p, de.name, DIRSIZ);
p[DIRSIZ] = 0;
if(stat(buf, &st) < 0){
printf("find: cannot stat %s\n", buf);
continue;
}
if(st.type == T_DIR){
find_helper(buf, target);
}else if (st.type == T_FILE){
if (strcmp(de.name, target) == 0)
{
printf("%s\n", buf);
}
}
}
break;
}
close(fd);
}
int main(int argc, char const *argv[])
{
if (argc != 3)
{
fprintf(2, "Usage: find dir file\n");
exit(1);
}
char const *path = argv[1];
char const *target = argv[2];
find_helper(path, target);
exit(0);
}简易版的xargs实现
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/param.h"
int readline(char *new_argv[32], int curr_argc){
char buf[1024];
int n = 0;
while(read(0, buf+n, 1)){
if (n == 1023)
{
fprintf(2, "argument is too long\n");
exit(1);
}
if (buf[n] == '\n')
{
break;
}
n++;
}
buf[n] = 0;
if (n == 0)return 0;
int offset = 0;
while(offset < n){
new_argv[curr_argc++] = buf + offset;
while(buf[offset] != ' ' && offset < n){
offset++;
}
while(buf[offset] == ' ' && offset < n){
buf[offset++] = 0;
}
}
return curr_argc;
}
int main(int argc, char const *argv[])
{
if (argc <= 1)
{
fprintf(2, "Usage: xargs command (arg ...)\n");
exit(1);
}
char *command = malloc(strlen(argv[1]) + 1);
char *new_argv[MAXARG];
strcpy(command, argv[1]);
for (int i = 1; i < argc; ++i)
{
new_argv[i - 1] = malloc(strlen(argv[i]) + 1);
strcpy(new_argv[i - 1], argv[i]);
}
int curr_argc;
while((curr_argc = readline(new_argv, argc - 1)) != 0)
{
new_argv[curr_argc] = 0;
if(fork() == 0){
exec(command, new_argv);
fprintf(2, "exec failed\n");
exit(1);
}
wait(0);
}
exit(0);
}