20145331 "Information Security system Design Fundamentals" 9th Week Study Summary

20145331 "The basis of information security system Design" 9th Week Study Summary Textbook learning Contents 10.1 Unix I/O

All I/O devices in Unix are modeled as files, and all inputs and outputs are executed as read and write to the corresponding file.

10.2 Open Close File

1. Open File:

int open(char *filename, int flags,mode_t mode);

Where the first parameter in parentheses is a file name, the second parameter is the way to access the file (3 kinds), and the third parameter is the access permission bit (mode&~umask).

2. Close the file:

int close(int fd);   

10.3 Read and write files

读：ssize_t read(int fd, void *buf, size_t n);写：ssize_t write(int fd, const void *buf, size_t n);

Note that there are differences between ssize_t and size_t.

10.3RIO Packet Read/write

1, the Rio package will automatically handle the insufficient value.

2, divided into two types of functions: unbuffered input and output functions (binary), buffered input functions (binary + text lines).

3, the first class read and write:

读：ssize_t rio_readn(int fd,void *usrbuf,size_t n);写：ssize_t rio_writen(int fd,void *usrbuf,size_t n);

4. Second class reading (three functions):

带缓冲顾名思义就先联系缓冲区：void rio_readinitb(rio_t *rp,int fd);接着读：ssize_t rio_readlineb(rio_t *rp,void *usrbuf,size_t maxlen);ssize_t rio_writen(rio_t *rp,void *usrbuf,size_t n);

10.5 Read File meta data

1, the file element is the file information, call Stat and Fstat function to retrieve information about the file

int stat(const char *filename,struct stat *buf);int fstat(int fd,struct stat *buf);

2, where the St_size member contains the file's byte size. St_mode is the file access License bit.

10.6 Sharing files

1, three structure:
Descriptor table: Stand-alone file tables: Multi-part, process-sharing. V-node table: Process sharing. 2, the key: Each descriptor has its own file location, different operators can read from different locations to obtain data.

10.7I/O redirection

1. Use dup2 function redirection.

int dup2(int oidfd,int newfd);

2, this section looked for a long time, from the example to understand: the previous two descriptors to a, b two files, now call the above function, all point to a file (if it is B), a is closed, its file table and the V-node table is deleted, the reference count of B is increased; later data is redirected to File B.

10.8 Standard I/O

1.

标准I/O库（libc）：高级输入输出函数fopen/fclose：打开和关闭文件fread/fwrite：读和写字节fgets/fputs：读和写字符串scanf/printf：复杂格式化的I/O函数

2. There are three open streams at the beginning of each program:

stdin：标准输入stdout：标准输出stderr：标准错误

Problems encountered in textbook learning:

10.1:

The return value of the Open function: The descriptor of the new file if successful, or 1 if an error occurs

Each process starts with three files open: standard input, standard output, standard error. They have descriptors of 0, 1, and 2, respectively. Therefore, FD1 returns a descriptor of 3. The close function is then called, releasing the descriptor 3. So the return value of FD2 is the descriptor 3.

10.2:

10-12. FD1 and FD2 correspond to different descriptor tables, but they also correspond to different file table entries, but they correspond to the V-note table, which is open foobar.txt. So read the first byte of foobar, output F

10.3:

10-13. First you know that the DAO Zi process is equivalent to copying the parent process, OK so the parent process is the same as the Descriptor table, file table, V-note tables correspondence and child processes. Descriptor FD points to the same file table entry in the parent-child process. So when the child process has finished reading, the parent process reads O, and the output O

10.4:

Dup2 (A, A, b) refers to the redirection of a to a, and a copy to the B standard input descriptor is 0

10.5:

Dup2 (FD2,FD1) fd2 Copy to Fd1,fd1 is redirected to FD2. So after performing the read again, the output is O

Problems encountered in the code:

The p598 code found at the start of compiling the book does not have "csapp.h":

Workaround: See the book p597 code above the header file, try it, compile and run it successfully:

These three header files are equivalent to "csapp.h".

Code hosting:

Refer to the teacher's comments this week code hosting made a link form:

Dot me to order me!

And the relevant instructions are used to statistic:

Experience:

Content seems to be very small, but more difficult to understand than before, also spent a lot of time to read, my experience is to see this chapter must learn to find different, this is the key; from next week to learn the C language, it feels like reading some basic code is very laborious.

Learning progress Bar /Cumulative) new/cumulative)

	lines of code (new	Blog volume (	Learning time (new/cumulative)	Important growth
Goal	5000 rows	30 Articles	400 hours
7th Week	67/472	1/10	20/151

20145331 "Information Security system Design Fundamentals" 9th Week Study Summary