2018-2019-1 20165226 《信息安全系统设计基础》第6周学习总结

目录

• 一、教材学习内容总结
• 二、练习
• 三、代码托管与统计
• 四、学习进度条
• 五、参考资料

一、教材学习内容总结

1、 Unix I/O

这一节涉及到操作系统的基本抽象之一——文件。也就是说，所有的I/O设备都被模型化为文件，而所有的输入输出都被当做对相应文件的读/写。

• I/O设备：网络、磁盘和终端
  • 描述符：打开文件时，内核返回一个小的非负整数。
  • Unix外壳创建的每个进程开始时都有三个打开的文件：标准输入（描述符为0）、标准输出（描述符为1）、标准错误（描述符为2）。
  • 改变当前的文件位置：文件位置为k，初始为0。
  • seek操作：显式地设置文件的当前位置为k。
  • 关闭文件：内核释放文件打开时创建的数据结构，并将这个描述符恢复到可用的描述符池中。无论一个进程因为何种原因终止时，内核都会关闭所有打开的文件并释放它们的存储器资源。

2、打开和关闭文件

（1）open函数：打开一个已存在的文件或者创建一个新文件

• 定义：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>int open(char *filename,int flags,mode_t mode)；

• 参数解析：
  • 返回值：类型为int型，返回的是描述符数字，总是在进程中当前没有打开的最小描述符。如果出错，返回值为-1.
  • filename：文件名
  • flags：指明进程打算如何访问这个文件，可以取的值见下：

  O_RDONLY：只读O_WRONLY：只写O_RDWR：可读可写O_CREAT：文件不存在，就创建新文件O_TRUNC：如果文件存在，就截断它O_APPEND：写操作前设置文件位置到结尾处

这些值可以用或连接起来。
- mode：指定了新文件的访问权限位，符号名称如下：

（2）close函数

• 函数定义

#include <unistd.h>
int close(int fd);

• 参数解析

  • 返回值：成功返回0，出错返回-1

    关闭一个已经关闭的描述符会出错

  • fd：即文件的描述符。

3、读和写文件

• 应用程序是通过分别调用read和write函数来执行输入和输出的。

#include <unistd.h>
ssize_t read(int fd,void *buf,size_t n);
ssize_t write(int fd,const void *buf,size_t n);

read函数：从描述符为fd的当前文件位置拷贝最多n个字节到存储器位置buf。返回值：-1表示一个错误；0表示EOF；否则，返回值表示的是实际传送的字节数量。
从存储器位置buf拷贝至多n个字节到描述符fd的当前文件位置。返回值：若成功则为写的字节数，若出错则为-1。

• lseek函数：应用程序能够显式地修改当前文件的位置。
• 不足值：read和write传送的字节比应用程序要求的少。
  • 读时遇到EOF
  • 从终端读文本行
  • 读和写网络套接字

4、用RIO包健壮的读写

RIO包的实质：I/O包
RIO包提供的两种函数：

• 无缓冲的输入输出函数
• 带缓冲的输入函数（线程安全）

RIO的无缓冲的输入输出函数

• 应用程序通过调用rioreadn和riowritten函数可以在存储器和文件之间直接传送数据。

#include "csapp.h"
ssize_t rio_readn(int fd,void *usrbuf,size_t n);
ssize_t rio_writen(int fd,void *usrbuf,size_t n);

• rio_ readn函数在遇到EOF时，只能返回一个不足值；
• rio_ writen函数绝不会返回不足值。

RIO的带缓冲的输入函数

• 一个文本行就是一个由换行符结尾的ASCII码字符序列。在Unix系统中，换行符（‘\n'）与ASCII码换行符（LF）相同，数字值为0x0a。
• 计算文本文件中文本行的数量，更好地方法是：
  • 调用一个包装函数（rio、readlineb），它从一个内部读缓冲区拷贝一个文本行，当缓冲区变空时，会自动地调用read重新填满缓冲区。

#include "csapp.h"
//每打开一个描述符都会调用一次该函数，它将描述符fd和地址rp处的类型为rio_t的缓冲区联系起来。
void rio_readinitb(rio_t *rp,int fd);
//从文件rp中读取一个文本行（包括结尾的换行符），将它拷贝到存储器位置usrbuf，并用空字符来结束这个文本行。
ssize_t rio_readlineb(rio_t *rp,void *usrbuf,size_t maxlen);
//从文件rp中最多读n个字节到存储器位置usrbuf。对同一描述符，rioreadnb和rioreadlineb的调用可以交叉进行。
ssize_t rio_readnb(rio_t *rp,void *usrbuf,size_t n);

读取文件元数据

• 检索文件信息（元数据）：应用程序能够通过调用stat和fstat函数

#include <unistd.h>
#include <sys/stat.h>
int stat(const char *filename,struct stat *buf);
//stat函数以一个文件名作为输入，填写一个stat数据结构中的各个成员。
int fstat(int fd,struct stat *buf);
//fstat函数以文件描述符而不是文件名作为输入。

• st_size成员包含了文件的字节数大小
• st_mode成员编码了文件访问许可位和文件类型
• Unix提供的宏指令根据st_mode成员来确定文件的类型

返回目录

二、练习

练习题10.1

#include "csapp.h"
int main(){int fd1,fd2;fd1=Open("foo.txt",O_RDONLY,0);Close(fd1);fd2=Open("baz.txt",O_RDONLY,0);print("fd2=%d\n",fd2);exit(0);}

• 编译时发生错误：
  

• 说明是Linux系统没有自带csapp/h头文件，需要自己编写。所以，只要把这个头文件加入到系统的include目录中就好了。
  • csapp.h

/* $begin csapp.h */
#ifndef __CSAPP_H__
#define __CSAPP_H__
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <setjmp.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>
#include <math.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
/* Default file permissions are DEF_MODE & ~DEF_UMASK */
/* $begin createmasks */
#define DEF_MODE   S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH
#define DEF_UMASK  S_IWGRP|S_IWOTH
/* $end createmasks */
/* Simplifies calls to bind(), connect(), and accept() */
/* $begin sockaddrdef */
typedef struct sockaddr SA;
/* $end sockaddrdef */
/* Persistent state for the robust I/O (Rio) package */
/* $begin rio_t */
#define RIO_BUFSIZE 8192
typedef struct {int rio_fd;                /* descriptor for this internal buf */int rio_cnt;               /* unread bytes in internal buf */char *rio_bufptr;          /* next unread byte in internal buf */char rio_buf[RIO_BUFSIZE]; /* internal buffer */
} rio_t;
/* $end rio_t */
/* External variables */
extern int h_errno;    /* defined by BIND for DNS errors */
extern char **environ; /* defined by libc */
/* Misc constants */
#define MAXLINE  8192  /* max text line length */
#define MAXBUF   8192  /* max I/O buffer size */
#define LISTENQ  1024  /* second argument to listen() */
/* Our own error-handling functions */
void unix_error(char *msg);
void posix_error(int code, char *msg);
void dns_error(char *msg);
void app_error(char *msg);
/* Process control wrappers */
pid_t Fork(void);
void Execve(const char *filename, char *const argv[], char *const envp[]);
pid_t Wait(int *status);
pid_t Waitpid(pid_t pid, int *iptr, int options);
void Kill(pid_t pid, int signum);
unsigned int Sleep(unsigned int secs);
void Pause(void);
unsigned int Alarm(unsigned int seconds);
void Setpgid(pid_t pid, pid_t pgid);
pid_t Getpgrp();/* Signal wrappers */
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);
void Sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
void Sigemptyset(sigset_t *set);
void Sigfillset(sigset_t *set);
void Sigaddset(sigset_t *set, int signum);
void Sigdelset(sigset_t *set, int signum);
int Sigismember(const sigset_t *set, int signum);
/* Unix I/O wrappers */
int Open(const char *pathname, int flags, mode_t mode);
ssize_t Read(int fd, void *buf, size_t count);
ssize_t Write(int fd, const void *buf, size_t count);
off_t Lseek(int fildes, off_t offset, int whence);
void Close(int fd);
int Select(int  n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
int Dup2(int fd1, int fd2);
void Stat(const char *filename, struct stat *buf);
void Fstat(int fd, struct stat *buf) ;
/* Memory mapping wrappers */
void *Mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset);
void Munmap(void *start, size_t length);
/* Standard I/O wrappers */
void Fclose(FILE *fp);
FILE *Fdopen(int fd, const char *type);
char *Fgets(char *ptr, int n, FILE *stream);
FILE *Fopen(const char *filename, const char *mode);
void Fputs(const char *ptr, FILE *stream);
size_t Fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
void Fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);
/* Dynamic storage allocation wrappers */
void *Malloc(size_t size);
void *Realloc(void *ptr, size_t size);
void *Calloc(size_t nmemb, size_t size);
void Free(void *ptr);
/* Sockets interface wrappers */
int Socket(int domain, int type, int protocol);
void Setsockopt(int s, int level, int optname, const void *optval, int optlen);
void Bind(int sockfd, struct sockaddr *my_addr, int addrlen);
void Listen(int s, int backlog);
int Accept(int s, struct sockaddr *addr, socklen_t *addrlen);
void Connect(int sockfd, struct sockaddr *serv_addr, int addrlen);
/* DNS wrappers */
struct hostent *Gethostbyname(const char *name);
struct hostent *Gethostbyaddr(const char *addr, int len, int type);
/* Pthreads thread control wrappers */
void Pthread_create(pthread_t *tidp, pthread_attr_t *attrp, void * (*routine)(void *), void *argp);
void Pthread_join(pthread_t tid, void **thread_return);
void Pthread_cancel(pthread_t tid);
void Pthread_detach(pthread_t tid);
void Pthread_exit(void *retval);
pthread_t Pthread_self(void);
void Pthread_once(pthread_once_t *once_control, void (*init_function)());
/* POSIX semaphore wrappers */
void Sem_init(sem_t *sem, int pshared, unsigned int value);
void P(sem_t *sem);
void V(sem_t *sem);/* Rio (Robust I/O) package */
ssize_t rio_readn(int fd, void *usrbuf, size_t n);
ssize_t rio_writen(int fd, void *usrbuf, size_t n);
void rio_readinitb(rio_t *rp, int fd);
ssize_t rio_readnb(rio_t *rp, void *usrbuf, size_t n);
ssize_t rio_readlineb(rio_t *rp, void *usrbuf, size_t maxlen);
/* Wrappers for Rio package */
ssize_t Rio_readn(int fd, void *usrbuf, size_t n);
void Rio_writen(int fd, void *usrbuf, size_t n);
void Rio_readinitb(rio_t *rp, int fd);
ssize_t Rio_readnb(rio_t *rp, void *usrbuf, size_t n);
ssize_t Rio_readlineb(rio_t *rp, void *usrbuf, size_t maxlen);
/* Client/server helper functions */
int open_clientfd(char *hostname, int portno);
int open_listenfd(int portno);
/* Wrappers for client/server helper functions */
int Open_clientfd(char *hostname, int port);
int Open_listenfd(int port);
#include <csapp.c>
#endif /* __CSAPP_H__ */
/* $end csapp.h */

• csappp.c

/* $begin csapp.c */
#include "csapp.h"
/************************** * Error-handling functions**************************/
/* $begin errorfuns */
/* $begin unixerror */
void unix_error(char *msg) /* unix-style error */
{fprintf(stderr, "%s: %s\n", msg, strerror(errno));exit(0);
}
/* $end unixerror */
void posix_error(int code, char *msg) /* posix-style error */
{fprintf(stderr, "%s: %s\n", msg, strerror(code));exit(0);
}
void dns_error(char *msg) /* dns-style error */
{fprintf(stderr, "%s: DNS error %d\n", msg, h_errno);exit(0);
}
void app_error(char *msg) /* application error */
{fprintf(stderr, "%s\n", msg);exit(0);
}
/* $end errorfuns */
/********************************************** Wrappers for Unix process control functions********************************************/
/* $begin forkwrapper */
pid_t Fork(void)
{pid_t pid;if ((pid = fork()) < 0)unix_error("Fork error");return pid;
}
/* $end forkwrapper */
void Execve(const char *filename, char *const argv[], char *const envp[])
{if (execve(filename, argv, envp) < 0)unix_error("Execve error");
}
/* $begin wait */
pid_t Wait(int *status)
{pid_t pid;if ((pid  = wait(status)) < 0)unix_error("Wait error");return pid;
}
/* $end wait */pid_t Waitpid(pid_t pid, int *iptr, int options)
{pid_t retpid;if ((retpid  = waitpid(pid, iptr, options)) < 0) unix_error("Waitpid error");return(retpid);
}
/* $begin kill */
void Kill(pid_t pid, int signum)
{int rc;if ((rc = kill(pid, signum)) < 0)unix_error("Kill error");
}
/* $end kill */
void Pause()
{(void)pause();return;
}
unsigned int Sleep(unsigned int secs)
{unsigned int rc;if ((rc = sleep(secs)) < 0)unix_error("Sleep error");return rc;
}
unsigned int Alarm(unsigned int seconds) {return alarm(seconds);
}
void Setpgid(pid_t pid, pid_t pgid) {int rc;if ((rc = setpgid(pid, pgid)) < 0)unix_error("Setpgid error");return;
}
pid_t Getpgrp(void) {return getpgrp();
}
/************************************* Wrappers for Unix signal functions ***********************************/
/* $begin sigaction */
handler_t *Signal(int signum, handler_t *handler)
{struct sigaction action, old_action;action.sa_handler = handler;  sigemptyset(&action.sa_mask); /* block sigs of type being handled */action.sa_flags = SA_RESTART; /* restart syscalls if possible */if (sigaction(signum, &action, &old_action) < 0)unix_error("Signal error");return (old_action.sa_handler);
}
/* $end sigaction */
void Sigprocmask(int how, const sigset_t *set, sigset_t *oldset)
{if (sigprocmask(how, set, oldset) < 0)unix_error("Sigprocmask error");return;
}
void Sigemptyset(sigset_t *set)
{if (sigemptyset(set) < 0)unix_error("Sigemptyset error");return;
}
void Sigfillset(sigset_t *set)
{ if (sigfillset(set) < 0)unix_error("Sigfillset error");return;
}
void Sigaddset(sigset_t *set, int signum)
{if (sigaddset(set, signum) < 0)unix_error("Sigaddset error");return;
}
void Sigdelset(sigset_t *set, int signum)
{if (sigdelset(set, signum) < 0)unix_error("Sigdelset error");return;
}
int Sigismember(const sigset_t *set, int signum)
{int rc;if ((rc = sigismember(set, signum)) < 0)unix_error("Sigismember error");return rc;
}
/********************************* Wrappers for Unix I/O routines********************************/
int Open(const char *pathname, int flags, mode_t mode)
{int rc;if ((rc = open(pathname, flags, mode))  < 0)unix_error("Open error");return rc;
}
ssize_t Read(int fd, void *buf, size_t count)
{ssize_t rc;if ((rc = read(fd, buf, count)) < 0) unix_error("Read error");return rc;
}
ssize_t Write(int fd, const void *buf, size_t count)
{ssize_t rc;if ((rc = write(fd, buf, count)) < 0)unix_error("Write error");return rc;
}
off_t Lseek(int fildes, off_t offset, int whence)
{off_t rc;if ((rc = lseek(fildes, offset, whence)) < 0)unix_error("Lseek error");return rc;
}
void Close(int fd)
{int rc;if ((rc = close(fd)) < 0)unix_error("Close error");
}
int Select(int  n, fd_set *readfds, fd_set *writefds,fd_set *exceptfds, struct timeval *timeout)
{int rc;if ((rc = select(n, readfds, writefds, exceptfds, timeout)) < 0)unix_error("Select error");return rc;
}
int Dup2(int fd1, int fd2)
{int rc;if ((rc = dup2(fd1, fd2)) < 0)unix_error("Dup2 error");return rc;
}
void Stat(const char *filename, struct stat *buf)
{if (stat(filename, buf) < 0)unix_error("Stat error");
}
void Fstat(int fd, struct stat *buf)
{if (fstat(fd, buf) < 0)unix_error("Fstat error");
}
/**************************************** Wrappers for memory mapping functions***************************************/
void *Mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset)
{void *ptr;if ((ptr = mmap(addr, len, prot, flags, fd, offset)) == ((void *) -1))unix_error("mmap error");return(ptr);
}
void Munmap(void *start, size_t length)
{if (munmap(start, length) < 0)unix_error("munmap error");
}
/**************************************************** Wrappers for dynamic storage allocation functions***************************************************/
void *Malloc(size_t size)
{void *p;if ((p  = malloc(size)) == NULL)unix_error("Malloc error");return p;
}
void *Realloc(void *ptr, size_t size)
{void *p;if ((p  = realloc(ptr, size)) == NULL)unix_error("Realloc error");return p;
}
void *Calloc(size_t nmemb, size_t size)
{void *p;if ((p = calloc(nmemb, size)) == NULL)unix_error("Calloc error");return p;
}
void Free(void *ptr)
{free(ptr);
}
/******************************************* Wrappers for the Standard I/O functions.******************************************/
void Fclose(FILE *fp)
{if (fclose(fp) != 0)unix_error("Fclose error");
}
FILE *Fdopen(int fd, const char *type)
{FILE *fp;if ((fp = fdopen(fd, type)) == NULL)unix_error("Fdopen error");return fp;
}
char *Fgets(char *ptr, int n, FILE *stream)
{char *rptr;if (((rptr = fgets(ptr, n, stream)) == NULL) && ferror(stream))app_error("Fgets error");return rptr;
}
FILE *Fopen(const char *filename, const char *mode)
{FILE *fp;if ((fp = fopen(filename, mode)) == NULL)unix_error("Fopen error");return fp;
}
void Fputs(const char *ptr, FILE *stream)
{if (fputs(ptr, stream) == EOF)unix_error("Fputs error");
}
size_t Fread(void *ptr, size_t size, size_t nmemb, FILE *stream)
{size_t n;if (((n = fread(ptr, size, nmemb, stream)) < nmemb) && ferror(stream)) unix_error("Fread error");return n;
}
void Fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream)
{if (fwrite(ptr, size, nmemb, stream) < nmemb)unix_error("Fwrite error");
}
/**************************** * Sockets interface wrappers****************************/
int Socket(int domain, int type, int protocol)
{int rc;if ((rc = socket(domain, type, protocol)) < 0)unix_error("Socket error");return rc;
}
void Setsockopt(int s, int level, int optname, const void *optval, int optlen)
{int rc;if ((rc = setsockopt(s, level, optname, optval, optlen)) < 0)unix_error("Setsockopt error");
}
void Bind(int sockfd, struct sockaddr *my_addr, int addrlen)
{int rc;if ((rc = bind(sockfd, my_addr, addrlen)) < 0)unix_error("Bind error");
}
void Listen(int s, int backlog)
{int rc;if ((rc = listen(s,  backlog)) < 0)unix_error("Listen error");
}int Accept(int s, struct sockaddr *addr, socklen_t *addrlen)
{int rc;if ((rc = accept(s, addr, addrlen)) < 0)unix_error("Accept error");return rc;
}
void Connect(int sockfd, struct sockaddr *serv_addr, int addrlen)
{int rc;if ((rc = connect(sockfd, serv_addr, addrlen)) < 0)unix_error("Connect error");
}
/************************* DNS interface wrappers ***********************/
/* $begin gethostbyname */
struct hostent *Gethostbyname(const char *name)
{struct hostent *p;if ((p = gethostbyname(name)) == NULL)dns_error("Gethostbyname error");return p;
}
/* $end gethostbyname */
struct hostent *Gethostbyaddr(const char *addr, int len, int type)
{struct hostent *p;if ((p = gethostbyaddr(addr, len, type)) == NULL)dns_error("Gethostbyaddr error");return p;
}
/************************************************* Wrappers for Pthreads thread control functions************************************************/
void Pthread_create(pthread_t *tidp, pthread_attr_t *attrp, void * (*routine)(void *), void *argp)
{int rc;if ((rc = pthread_create(tidp, attrp, routine, argp)) != 0)posix_error(rc, "Pthread_create error");
}
void Pthread_cancel(pthread_t tid) {int rc;if ((rc = pthread_cancel(tid)) != 0)posix_error(rc, "Pthread_cancel error");
}
void Pthread_join(pthread_t tid, void **thread_return) {int rc;if ((rc = pthread_join(tid, thread_return)) != 0)posix_error(rc, "Pthread_join error");
}
/* $begin detach */
void Pthread_detach(pthread_t tid) {int rc;if ((rc = pthread_detach(tid)) != 0)posix_error(rc, "Pthread_detach error");
}
/* $end detach */
void Pthread_exit(void *retval) {pthread_exit(retval);
}
pthread_t Pthread_self(void) {return pthread_self();
}
void Pthread_once(pthread_once_t *once_control, void (*init_function)()) {pthread_once(once_control, init_function);
}
/******************************** Wrappers for Posix semaphores*******************************/
void Sem_init(sem_t *sem, int pshared, unsigned int value)
{if (sem_init(sem, pshared, value) < 0)unix_error("Sem_init error");
}
void P(sem_t *sem)
{if (sem_wait(sem) < 0)unix_error("P error");
}
void V(sem_t *sem)
{if (sem_post(sem) < 0)unix_error("V error");
}
/********************************************************************** The Rio package - robust I/O functions**********************************************************************/
/** rio_readn - robustly read n bytes (unbuffered)*/
/* $begin rio_readn */
ssize_t rio_readn(int fd, void *usrbuf, size_t n)
{size_t nleft = n;ssize_t nread;char *bufp = usrbuf;while (nleft > 0) {if ((nread = read(fd, bufp, nleft)) < 0) {if (errno == EINTR) /* interrupted by sig handler return */nread = 0;      /* and call read() again */elsereturn -1;      /* errno set by read() */ } else if (nread == 0)break;              /* EOF */nleft -= nread;bufp += nread;}return (n - nleft);         /* return >= 0 */
}
/* $end rio_readn *//** rio_writen - robustly write n bytes (unbuffered)*/
/* $begin rio_writen */
ssize_t rio_writen(int fd, void *usrbuf, size_t n)
{size_t nleft = n;ssize_t nwritten;char *bufp = usrbuf;while (nleft > 0) {if ((nwritten = write(fd, bufp, nleft)) <= 0) {if (errno == EINTR)  /* interrupted by sig handler return */nwritten = 0;    /* and call write() again */elsereturn -1;       /* errno set by write() */}nleft -= nwritten;bufp += nwritten;}return n;
}
/* $end rio_writen */
/* * rio_read - This is a wrapper for the Unix read() function that*    transfers min(n, rio_cnt) bytes from an internal buffer to a user*    buffer, where n is the number of bytes requested by the user and*    rio_cnt is the number of unread bytes in the internal buffer. On*    entry, rio_read() refills the internal buffer via a call to*    read() if the internal buffer is empty.*/
/* $begin rio_read */
static ssize_t rio_read(rio_t *rp, char *usrbuf, size_t n)
{int cnt;while (rp->rio_cnt <= 0) {  /* refill if buf is empty */rp->rio_cnt = read(rp->rio_fd, rp->rio_buf, sizeof(rp->rio_buf));if (rp->rio_cnt < 0) {if (errno != EINTR) /* interrupted by sig handler return */return -1;}else if (rp->rio_cnt == 0)  /* EOF */return 0;else rp->rio_bufptr = rp->rio_buf; /* reset buffer ptr */}/* Copy min(n, rp->rio_cnt) bytes from internal buf to user buf */cnt = n;          if (rp->rio_cnt < n)   cnt = rp->rio_cnt;memcpy(usrbuf, rp->rio_bufptr, cnt);rp->rio_bufptr += cnt;rp->rio_cnt -= cnt;return cnt;
}
/* $end rio_read *//** rio_readinitb - Associate a descriptor with a read buffer and reset buffer*/
/* $begin rio_readinitb */
void rio_readinitb(rio_t *rp, int fd)
{rp->rio_fd = fd;  rp->rio_cnt = 0;  rp->rio_bufptr = rp->rio_buf;
}
/* $end rio_readinitb */
/** rio_readnb - Robustly read n bytes (buffered)*/
/* $begin rio_readnb */
ssize_t rio_readnb(rio_t *rp, void *usrbuf, size_t n)
{size_t nleft = n;ssize_t nread;char *bufp = usrbuf;while (nleft > 0) {if ((nread = rio_read(rp, bufp, nleft)) < 0) {if (errno == EINTR) /* interrupted by sig handler return */nread = 0;      /* call read() again */elsereturn -1;      /* errno set by read() */ } else if (nread == 0)break;              /* EOF */nleft -= nread;bufp += nread;}return (n - nleft);         /* return >= 0 */
}
/* $end rio_readnb */
/* * rio_readlineb - robustly read a text line (buffered)*/
/* $begin rio_readlineb */
ssize_t rio_readlineb(rio_t *rp, void *usrbuf, size_t maxlen)
{int n, rc;char c, *bufp = usrbuf;for (n = 1; n < maxlen; n++) { if ((rc = rio_read(rp, &c, 1)) == 1) {*bufp++ = c;if (c == '\n')break;} else if (rc == 0) {if (n == 1)return 0; /* EOF, no data read */elsebreak;    /* EOF, some data was read */} elsereturn -1;    /* error */}*bufp = 0;return n;
}
/* $end rio_readlineb *//*********************************** Wrappers for robust I/O routines**********************************/
ssize_t Rio_readn(int fd, void *ptr, size_t nbytes)
{ssize_t n;if ((n = rio_readn(fd, ptr, nbytes)) < 0)unix_error("Rio_readn error");return n;
}
void Rio_writen(int fd, void *usrbuf, size_t n)
{if (rio_writen(fd, usrbuf, n) != n)unix_error("Rio_writen error");
}
void Rio_readinitb(rio_t *rp, int fd)
{rio_readinitb(rp, fd);
}
ssize_t Rio_readnb(rio_t *rp, void *usrbuf, size_t n)
{ssize_t rc;if ((rc = rio_readnb(rp, usrbuf, n)) < 0)unix_error("Rio_readnb error");return rc;
}
ssize_t Rio_readlineb(rio_t *rp, void *usrbuf, size_t maxlen)
{ssize_t rc;if ((rc = rio_readlineb(rp, usrbuf, maxlen)) < 0)unix_error("Rio_readlineb error");return rc;
}
/******************************** * Client/server helper functions********************************/
/** open_clientfd - open connection to server at <hostname, port> *   and return a socket descriptor ready for reading and writing.*   Returns -1 and sets errno on Unix error. *   Returns -2 and sets h_errno on DNS (gethostbyname) error.*/
/* $begin open_clientfd */
int open_clientfd(char *hostname, int port)
{int clientfd;struct hostent *hp;struct sockaddr_in serveraddr;if ((clientfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)return -1; /* check errno for cause of error *//* Fill in the server's IP address and port */if ((hp = gethostbyname(hostname)) == NULL)return -2; /* check h_errno for cause of error */bzero((char *) &serveraddr, sizeof(serveraddr));serveraddr.sin_family = AF_INET;bcopy((char *)hp->h_addr_list[0], (char *)&serveraddr.sin_addr.s_addr, hp->h_length);serveraddr.sin_port = htons(port);/* Establish a connection with the server */if (connect(clientfd, (SA *) &serveraddr, sizeof(serveraddr)) < 0)return -1;return clientfd;
}
/* $end open_clientfd */
/*  * open_listenfd - open and return a listening socket on port*     Returns -1 and sets errno on Unix error.*/
/* $begin open_listenfd */
int open_listenfd(int port)
{int listenfd, optval=1;struct sockaddr_in serveraddr;/* Create a socket descriptor */if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)return -1;/* Eliminates "Address already in use" error from bind. */if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&optval , sizeof(int)) < 0)return -1;/* Listenfd will be an endpoint for all requests to porton any IP address for this host */bzero((char *) &serveraddr, sizeof(serveraddr));serveraddr.sin_family = AF_INET; serveraddr.sin_addr.s_addr = htonl(INADDR_ANY); serveraddr.sin_port = htons((unsigned short)port); if (bind(listenfd, (SA *)&serveraddr, sizeof(serveraddr)) < 0)return -1;/* Make it a listening socket ready to accept connection requests */if (listen(listenfd, LISTENQ) < 0)return -1;return listenfd;
}
/* $end open_listenfd */
/******************************************* Wrappers for the client/server helper routines ******************************************/
int Open_clientfd(char *hostname, int port)
{int rc;if ((rc = open_clientfd(hostname, port)) < 0) {if (rc == -1)unix_error("Open_clientfd Unix error");else        dns_error("Open_clientfd DNS error");}return rc;
}
int Open_listenfd(int port)
{int rc;if ((rc = open_listenfd(port)) < 0)unix_error("Open_listenfd error");return rc;
}
/* $end csapp.c */

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三、代码托管与统计

****
代码托管

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四、学习进度条

尝试一下记录「计划学习时间」和「实际学习时间」，到期末看看能不能改进自己的计划能力。这个工作学习中很重要，也很有用。
耗时估计的公式
：Y=X+X/N ，Y=X-X/N，训练次数多了，X、Y就接近了。

参考：软件工程软件的估计为什么这么难，软件工程 估计方法

• 计划学习时间:8小时

• 实际学习时间:8小时

• 改进情况：

(有空多看看现代软件工程 课件
软件工程师能力自我评价表)

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五、参考资料

• 《深入理解计算机系统V3》学习指导
• Linux 基础入门（新版）_Linux_实验楼 - 实验楼

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