实验工具

• clone实验源码
  git clone git://g.csail.mit.edu/xv6-labs-2023
• 进入目录
  cd xv6-labs-2023
• 运行内核
  make qemu
• 打印数据
  Ctrl-p
• 退出
  ctr+a+x

xv6中的system call

int fork()  Create a process, return child’s PID. 
int exit(int status)  Terminate the current process; status reported to wait(). No return. 
int wait(int *status)  Wait for a child to exit; exit status in *status; returns child PID. 
int kill(int pid)  Terminate process PID. Returns 0, or -1 for error. 
int getpid()  Return the current process’s PID. 
int sleep(int n)  Pause for n clock ticks. 
int exec(char *file, char *argv[]) Load a file and execute it with arguments; only returns if error. char *sbrk(int n)  Grow process’s memory by n bytes. Returns start of new memory. 
int open(char *file, int flags)  Open a file; flags indicate read/write; returns an fd (file descriptor). 
int write(int fd, char *buf, int n) Write n bytes from buf to file descriptor fd; returns n. 
int read(int fd, char *buf, int n) Read n bytes into buf; returns number read; or 0 if end of file. 
int close(int fd)  Release open file fd. 
int dup(int fd)  Return a new file descriptor referring to the same file as fd. 
int pipe(int p[])  Create a pipe, put read/write file descriptors in p[0] and p[1]. 
int chdir(char *dir)  Change the current directory. 
int mkdir(char *dir)  Create a new directory. 
int mknod(char *file, int, int) Create a device file. 
int fstat(int fd, struct stat *st) Place info about an open file into *st. 
int stat(char *file, struct stat *st) Place info about a named file into *st. 
int link(char *file1, char *file2) Create another name (file2) for the file file1. 
int unlink(char *file)  Remove a file.

exit()

• 作用：系统调用，用于当前进程停止执行、释放资源。
• 返回值：0-成功，1-失败
• 具体作用：返回当前进程被的子进程（退出或杀死）的PID
  复制子进程的退出状态到等待序列

用户级睡眠程序