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Linux System Programming 学习笔记(八) 文件和目录管理

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1. 文件和元数据

每个文件都是通过inode引用,每个inode索引节点都具有文件系统中唯一的inode number
一个inode索引节点是存储在Linux文件系统的磁盘介质上的物理对象,也是LInux内核通过数据结构表示的实体
inode存储相关联文件的元数据
 
ls -i 命令获取文件的inode number
 
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/* obtaining the metadata of a file */
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int stat (const char *path, struct stat *buf);
int fstat (int fd, struct stat *buf);
int lstat (const char *path, struct stat *buf);
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注意:lstat函数可以获取 符号链接的文件元数据,lstat() returns information about the link itself and not the target file

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struct stat {
        dev_t      st_dev;         /* ID of device containing file */
        ino_t      st_ino;         /* inode number */
        mode_t     st_mode;        /* permissions */
        nlink_t    st_nlink;       /* number of hard links */
        uid_t      st_uid;         /* user ID of owner */
        gid_t      st_gid;         /* group ID of owner */
        dev_t      st_rdev;        /* device ID (if special file) */
        off_t      st_size;        /* total size in bytes */
        blksize_t  st_blksize;     /* blocksize for filesystem I/O */
        blkcnt_t   st_blocks;      /* number of blocks allocated */
        time_t     st_atime;       /* last access time */
        time_t     st_mtime;       /* last modification time */
        time_t     st_ctime;       /* last status change time */
};
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2. 目录
a directory contains a list of filenames, each of which maps to an inode number. Each name is called a directory entry, and each name-to-inode mapping is called a link
当打开给定目录中的文件,内核查询相应的inode编号,然后将inode编号传递给文件系统,文件系统使用inode编号来寻找相应的存储在物理介质中的文件
 
Reading a Directory’s Contents : 

 

/* creates a directory stream representing the directory given by name */
#include <sys/types.h>
#include <dirent.h>
DIR * opendir (const char *name);

 

/* returns the next entry in the directory represented by dir */
#include <sys/types.h>
#include <dirent.h>
struct dirent * readdir (DIR *dir);

 

/* closes the directory stream represented by dir */
#include <sys/types.h>
#include <dirent.h>
int closedir (DIR *dir);

 

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/*
 * find_file_in_dir - searches the directory ‘path‘ for a
 * file named ‘file‘.
 *
 * Returns 0 if ‘file‘ exists in ‘path‘ and a nonzero
 * value otherwise.
 */
int find_file_in_dir (const char *path, const char *file)
{
        struct dirent *entry;
        int ret = 1;
        DIR *dir;
        dir = opendir (path);
        errno = 0;
        while ((entry = readdir (dir)) != NULL) {
                if (strcmp(entry->d_name, file) == 0) {
                        ret = 0;
                        break;
                }
        }
        if (errno && !entry)
                perror ("readdir");
        closedir (dir);
        return ret;
}
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3. 链接
each name-to-inode mapping in a directory is called a link.
Most files have a link count of 1,that is, they are pointed at by a single directory entry
当一个文件的链接计数减为0时,文件被标记为free,如果存在进程仍在使用此文件,则该文件将保留在文件系统中
 
Linux内核使用 a link count and a usage count 实现,一个文件只有其link count和usage count都为0时,才会从文件系统移除
 
硬链接:
/* creates a new link under the path newpath for the existing file oldpath */
#include <unistd.h>
int link (const char *oldpath, const char *newpath);
成功调用之后,oldpath and newpath refer to the same file
 
符号链接(软链接):
软链接可以跨文件系统,链接到任何文件
/* creates the symbolic link newpath pointing at the target oldpath */
#include <unistd.h>
int symlink (const char *oldpath, const char *newpath);

解链:

#include <unistd.h>
int unlink (const char *pathname);
Once no process has the file open, it is deleted
 
4. Copying and Moving Files
 
Unix没有提供可以直接复制文件和目录的系统调用
 
 copying a file src to a file named dst:
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1). Open src.
2). Open dst, creating it if it does not exist, and truncating it to zero length if it does exist.
3). Read a chunk of src into memory.
4). Write the chunk to dst.
5). Continue until all of src has been read and written to dst.
6). Close dst.
7). Close src.
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5. 块设备
The null device lives at /dev/null. The kernel silently discards all write requests to the device. All read requests to the file return end-of-file (EOF).
The zero device lives at /dev/zero.  读此设备返回null字符,写此设备被丢弃
The full device lives at /dev/full.  读此设备返回null字符,写此设备将触发错误表示设备已满
The kernel‘s random number generators live at /dev/random. 

Linux System Programming 学习笔记(八) 文件和目录管理,布布扣,bubuko.com

Linux System Programming 学习笔记(八) 文件和目录管理

标签:c   style   class   blog   code   java   

原文地址:http://www.cnblogs.com/wwwjieo0/p/3756033.html

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