20135323符运锦--信息安全系统设计基础第十周学习总结

学习计时：共8小时

读书：1

代码：5

作业：0

博客：2

学习要求

代码阅读理解：

1. 编译运行代码
2. 使用man学习理解相关系统调用, 理解参数、返回值的含义
3. 会用grep -nr xxx /usr/include 查宏定义

cp1.c

echostate.c

fileinfo.c

filesize.c

ls1.c

ls2.c

setecho.c

spwd.c

testioctl.c

who1.c

who2.c

学习内容

1.cp

#include        <stdio.h>
#include        <stdlib.h>
#include        <unistd.h>
#include        <fcntl.h>//宏和open
define BUFFERSIZE      4096//存储器容量
#define COPYMODE        0644//复制长度
void oops(char *, char *);

int main(int argc, char *argv[])
{
int in_fd, out_fd, n_chars;//三个描述符值
char buf[BUFFERSIZE];

if (argc != 3) {
    fprintf(stderr, "usage: %s source destination\n", *argv);
    exit(1);
}
/*检查cp的第一个参数，要复制的文件，用open打开，in_fd为open返回的描述符*/
if ((in_fd = open(argv[1], O_RDONLY)) == -1)
    oops("Cannot open ", argv[1]);

/*检查cp的第二个参数，复制的目的地址，用create在目的地址创建新文件，out_fd为open返回的描述符*/
if ((out_fd = creat(argv[2], COPYMODE)) == -1)
    oops("Cannot creat", argv[2]);

/*cp指令的动作就是读取一个文件的内容到存储器，在新的地址创建空白文件，再从存储器将内容写入新文件。*/
while ((n_chars = read(in_fd, buf, BUFFERSIZE)) > 0)
    if (write(out_fd, buf, n_chars) != n_chars)
        oops("Write error to ", argv[2]);
if (n_chars == -1)
    oops("Read error from ", argv[1]);

if (close(in_fd) == -1 || close(out_fd) == -1)
    oops("Error closing files", "");
}

/*这个是用来输出错误信息的函数*/
void oops(char *s1, char *s2)
{
fprintf(stderr, "Error: %s ", s1);
perror(s2);
(stderr)
exit(1);
}

实现过程：1.开启源文件
2.创建目标文件
3.将源文件读入缓冲区
4.将缓冲区内容写入目标文件
5.关闭

2.ls1\ls2

1.ls -l 以长格式的形式查看当前目录下所有可见文件的详细属性

2.ls -a 列出的内容包含以“.”开头的文件

3.ls -lu 最后访问时间

4.ls -s 以块为单位的文件大小

5.ls -t 按时间排序

6.ls -F 显示文件类型

#include    <stdio.h>
#include    <sys/types.h>
#include    <dirent.h>

void do_ls(char []);

int main(int argc, char *argv[])
{
if ( argc == 1 )
    do_ls( "." );
else
    while ( --argc ){
        printf("%s:\n", *++argv );
        do_ls( *argv );
    }

return 0;
}

void do_ls( char dirname[] )
{
DIR     *dir_ptr;       
struct dirent   *direntp;       

if ( ( dir_ptr = opendir( dirname ) ) == NULL )
    fprintf(stderr,"ls1: cannot open %s\n", dirname);
else
{
    while ( ( direntp = readdir( dir_ptr ) ) != NULL )
        printf("%s\n", direntp->d_name );
    closedir(dir_ptr);
}
}

此函数用来显示文件的详细信息：用户名，群组名，大小，创建时间，读写执行权

#include    <stdio.h>
#include    <string.h>
#include    <sys/types.h>
#include    <dirent.h>
#include    <sys/stat.h>

void do_ls(char[]);
void dostat(char *);
void show_file_info( char *, struct stat *);
void mode_to_letters( int , char [] );
char *uid_to_name( uid_t );
char *gid_to_name( gid_t );

int main(int argc, char *argv[])
{
if ( argc == 1 )
    do_ls( "." );
else
    while ( --argc ){
        printf("%s:\n", *++argv );
        do_ls( *argv );
    }

return 0;
}

void do_ls( char dirname[] )
{
DIR     *dir_ptr;       
struct dirent   *direntp;       

if ( ( dir_ptr = opendir( dirname ) ) == NULL )
    fprintf(stderr,"ls1: cannot open %s\n", dirname);
else
{
    while ( ( direntp = readdir( dir_ptr ) ) != NULL )
        dostat( direntp->d_name );
    closedir(dir_ptr);
}
}

void dostat( char *filename )
{
struct stat info;

if ( stat(filename, &info) == -1 )      
    perror( filename );         
else                    
    show_file_info( filename, &info );
}

void show_file_info( char *filename, struct stat *info_p )
{
char    *uid_to_name(), *ctime(), *gid_to_name(), *filemode();
void    mode_to_letters();
    char    modestr[11];

mode_to_letters( info_p->st_mode, modestr );

printf( "%s"    , modestr );
printf( "%4d "  , (int) info_p->st_nlink);  
printf( "%-8s " , uid_to_name(info_p->st_uid) );
printf( "%-8s " , gid_to_name(info_p->st_gid) );
printf( "%8ld " , (long)info_p->st_size);
printf( "%.12s ", 4+ctime(&info_p->st_mtime));
printf( "%s\n"  , filename );

}

void mode_to_letters( int mode, char str[] )
{
strcpy( str, "----------" );           

if ( S_ISDIR(mode) )  str[0] = 'd';    
if ( S_ISCHR(mode) )  str[0] = 'c';    
if ( S_ISBLK(mode) )  str[0] = 'b';    

if ( mode & S_IRUSR ) str[1] = 'r';    
if ( mode & S_IWUSR ) str[2] = 'w';
if ( mode & S_IXUSR ) str[3] = 'x';

if ( mode & S_IRGRP ) str[4] = 'r';    
if ( mode & S_IWGRP ) str[5] = 'w';
if ( mode & S_IXGRP ) str[6] = 'x';

if ( mode & S_IROTH ) str[7] = 'r';    
if ( mode & S_IWOTH ) str[8] = 'w';
if ( mode & S_IXOTH ) str[9] = 'x';
}

#include    <pwd.h>

char *uid_to_name( uid_t uid )
{
struct  passwd *getpwuid(), *pw_ptr;
static  char numstr[10];

if ( ( pw_ptr = getpwuid( uid ) ) == NULL ){
    sprintf(numstr,"%d", uid);
    return numstr;
}
else
    return pw_ptr->pw_name ;
}

#include    <grp.h>

char *gid_to_name( gid_t gid )
{
struct group *getgrgid(), *grp_ptr;
static  char numstr[10];

if ( ( grp_ptr = getgrgid(gid) ) == NULL ){
    sprintf(numstr,"%d", gid);
    return numstr;
}
else
    return grp_ptr->gr_name;
}

ls2更加详细

3.echostate.c/setecho.c

#include        <stdio.h>
#include        <stdlib.h>
#include        <termios.h>

int main()
{
    struct termios info;
    int rv;

    rv = tcgetattr( 0, &info );     /* read values from driver      */

    if ( rv == -1 ){
            perror( "tcgetattr");
            exit(1);
    }
    if ( info.c_lflag & ECHO )
            printf(" echo is on , since its bit is 1\n");
    else
            printf(" echo is OFF, since its bit is 0\n");

    return 0;
}

echostate显示输入命令是否可见。其中：echo is on：命令可见；echo is off：命令不可见

 #include        <stdio.h>
#include        <stdlib.h>
#include        <termios.h>

#define  oops(s,x) { perror(s); exit(x); }

int main(int argc, char *argv[])
{
    struct termios info;

    if ( argc == 1 ) 
    exit(0);

    if ( tcgetattr(0,&info) == -1 )          /* get attribs   */
        oops("tcgettattr", 1);

    if ( argv[1][0] == 'y' )
            info.c_lflag |= ECHO ;          /* turn on bit    */
    else
            info.c_lflag &= ~ECHO ;         /* turn off bit   */

    if ( tcsetattr(0,TCSANOW,&info) == -1 ) /* set attribs    */
           oops("tcsetattr",2);

    return 0;
}

setecho用来改变输入指令是否可见。其中：输入y（或是以y开头的一串字符），命令可见；否则（即输入不以y开头的字符），命令不可见

4.fileinfo.c/filesize.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>

void show_stat_info(char *, struct stat *);

int main(int argc, char *argv[])
{
struct stat info;        

if (argc>1)
{

    if( stat(argv[1], &info) != -1 ){
        show_stat_info( argv[1], &info );
        return 0;
    }
    else
        perror(argv[1]);  
}
return 1;
}
void show_stat_info(char *fname, struct stat *buf)
{
printf("   mode: %o\n", buf->st_mode);         
printf("  links: %d\n", buf->st_nlink);        
printf("   user: %d\n", buf->st_uid);          
printf("  group: %d\n", buf->st_gid);          
printf("   size: %d\n", (int)buf->st_size);         
printf("modtime: %d\n", (int)buf->st_mtime);        
printf("   name: %s\n", fname );               
}

用来实现显示文件信息：
1.mode：st_mode//文件的类型和存取的权限
2.links：st_nlin//连到该文件的硬链接数目，刚建立的文件值为1
3.user：st_uid//用户ID
4.group：st_gid//组ID
5.size：st_size//文件字节数
6.modtime：st_mtime//最后一次修改时间
7.name： //输入的文件名

#include <stdio.h>
#include <sys/stat.h>

int main()
{
struct stat infobuf;           

if ( stat( "/etc/passwd", &infobuf) == -1 )
    perror("/etc/passwd");
else
    printf(" The size of /etc/passwd is %d\n", infobuf.st_size );
}

用st_size计算文件的字节数大小

5.spwd.c

#include    <stdio.h>
#include    <stdlib.h>
#include    <string.h>
#include    <sys/types.h>
#include    <sys/stat.h>
#include    <dirent.h>

ino_t   get_inode(char *);
void    printpathto(ino_t);
void    inum_to_name(ino_t , char *, int );

int main()
{
printpathto( get_inode( "." ) );    
putchar('\n');              
return 0;
}

void printpathto( ino_t this_inode )
{
ino_t   my_inode ;
char    its_name[BUFSIZ];

if ( get_inode("..") != this_inode )
{
    chdir( ".." );              

    inum_to_name(this_inode,its_name,BUFSIZ);

    my_inode = get_inode( "." );        
    printpathto( my_inode );        
    printf("/%s", its_name );       
                        
}
}

void inum_to_name(ino_t inode_to_find , char *namebuf, int buflen)
{
DIR     *dir_ptr;       
struct dirent   *direntp;       

dir_ptr = opendir( "." );
if ( dir_ptr == NULL ){
    perror( "." );
    exit(1);
}


while ( ( direntp = readdir( dir_ptr ) ) != NULL )
    if ( direntp->d_ino == inode_to_find )
    {
        strncpy( namebuf, direntp->d_name, buflen);
        namebuf[buflen-1] = '\0';   
        closedir( dir_ptr );
        return;
    }
fprintf(stderr, "error looking for inum %d\n", (int) inode_to_find);
exit(1);
}

ino_t get_inode( char *fname )
{
struct stat info;

if ( stat( fname , &info ) == -1 ){
    fprintf(stderr, "Cannot stat ");
    perror(fname);
    exit(1);
}
return info.st_ino;
}

列出当前目录

6.testioctl.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>

int main()
{
struct winsize size;
if( isatty(STDOUT_FILENO) == 0)
    exit(1);
if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &size) < 0) {
    perror("ioctl TIOCGWINSZ error");
    exit(1);
}

printf("%d rows %d columns\n", size.ws_row, size.ws_col);
return 0;
}

获得终端设备的窗口大小

7.who

#include    <stdio.h>
#include    <stdlib.h>
#include    <utmp.h>
#include    <fcntl.h>
#include    <unistd.h>

#define SHOWHOST    

int show_info( struct utmp *utbufp )
{
printf("%-8.8s", utbufp->ut_name);  
printf(" ");                
printf("%-8.8s", utbufp->ut_line);  
printf(" ");                
printf("%10ld", utbufp->ut_time);   
printf(" ");                
#ifdef  SHOWHOST
printf("(%s)", utbufp->ut_host);    
#endif
printf("\n");               

return 0;
}
int main()
{
struct utmp  current_record;    
int     utmpfd;     
int     reclen = sizeof(current_record);

if ( (utmpfd = open(UTMP_FILE, O_RDONLY)) == -1 ){
    perror( UTMP_FILE );    
    exit(1);
}
while ( read(utmpfd, &current_record, reclen) == reclen )
    show_info(&current_record);
close(utmpfd);
return 0;           
}

打开utmp文件，针对文件，读取想要的信息到存储器中，再用标准输出函数打印到屏幕上，关闭文件

参考资料

《深入理解计算机系统》

ls.tar视频