一、读取文件元数据
int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);
stat() stats the file pointed to by path and fills in buf.
lstat() is identical to stat(), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to.
fstat() is identical to stat(), except that the file to be stat-ed is specified by the file descriptor fd.
二、stat结构体
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */ 硬链接是不可以跨越文件系统的
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 file system I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
time_t st_atime; /* time of last access */ read
time_t st_mtime; /* time of last modification */ write
time_t st_ctime; /* time of last status change */ chmod/chown
};
示例程序：
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/*************************************************************************
> File Name: file_stat.c > Author: Simba > Mail: dameng34@163.com > Created Time: Sat 23 Feb 2013 02:34:02 PM CST ************************************************************************/ #include<sys/types.h> #include<sys/stat.h> #include<unistd.h> #include<fcntl.h> #include<stdio.h> #include<stdlib.h> #include<errno.h> #include<string.h> #define ERR_EXIT(m) do { perror(m); exit(EXIT_FAILURE); } while(0) #define MAJOR(a) (int)((unsigned short)a >> 8) // 高8位，主设备号 #define MINOR(a) (int)((unsigned short)a & 0xFF) int filetype(struct stat *buf) { int flag = 0; printf("Filetype:"); mode_t mode; mode = buf->st_mode; switch (mode & S_IFMT) { case S_IFSOCK: printf("socket "); break; case S_IFLNK: printf("symbolic link "); break; case S_IFREG: printf("regular file "); break; case S_IFBLK: printf("block device "); flag = 1; break; case S_IFDIR: printf("directory "); break; case S_IFCHR: printf("character device "); flag = 1; break; case S_IFIFO: printf("FIFO "); break; default: printf("unknown file type "); break; } return flag; } void fileperm(struct stat *buf, char perm[]) { strcpy(perm, "----------"); perm[0] = '?'; mode_t mode; mode = buf->st_mode; switch (mode & S_IFMT) { case S_IFSOCK: perm[0] = 's'; break; case S_IFLNK: perm[0] = 'l'; break; case S_IFREG: perm[0] = '-'; break; case S_IFBLK: perm[0] = 'b'; break; case S_IFDIR: perm[0] = 'd'; break; case S_IFCHR: perm[0] = 'c'; break; case S_IFIFO: perm[0] = 'p'; break; } if (mode & S_IRUSR) perm[1] = 'r'; if (mode & S_IWUSR) perm[2] = 'w'; if (mode & S_IXUSR) perm[3] = 'x'; if (mode & S_IRGRP) perm[4] = 'r'; if (mode & S_IWGRP) perm[5] = 'w'; if (mode & S_IXGRP) perm[6] = 'x'; if (mode & S_IROTH) perm[7] = 'r'; if (mode & S_IWOTH) perm[8] = 'w'; if (mode & S_IXOTH) perm[9] = 'x'; perm[10] = ' '; } int main(int argc, char *argv[]) { if (argc != 2) { fprintf(stderr, "Usage %s file ", argv[0]); exit(EXIT_FAILURE); } printf("Filename:%s ", argv[1]); struct stat sbuf; if (lstat(argv[1], &sbuf) == -1) ERR_EXIT("stat error"); printf("file in Dev number:major %d, minor %d ", MAJOR(sbuf.st_dev), MINOR(sbuf.st_dev)); printf("File inode:%d ", (int) sbuf.st_ino); if (filetype(&sbuf)) { printf("Device number:major %d, minor %d ", MAJOR(sbuf.st_rdev), MINOR(sbuf.st_rdev)); } char perm[11] = {0}; fileperm(&sbuf, perm); printf("File permission bits=%o %s ", sbuf.st_mode & 0777, perm); // 0777 是八进制数 return 0; } |
测试如下：
simba@ubuntu:~/Documents/code/linux_programming/APUE/File_IO$ ./file_stat Makefile
Filename:Makefile
file in Dev number:major 8, minor 1
File inode:660022
Filetype:regular file
File permission bits=664 -rw-rw-r--
因为是普通文件，故从st_dev字段看设备号，而不是st_rdev. 主设备号表示设备驱动程序，而次设备号表示特定的子设备。比如在同一个磁盘上面不同的文件系统，设备驱动程序相当，但是次设备号不同。
st_rdev只有字符特殊文件和块特殊文件才有这个值，表示实际设备的设备编号。
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The st_dev value for every filename on a system is the device number of the file system containing that filename and its corresponding
i-node.
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Only character special files and block special files have an st_rdev value. This value contains the device number for the actual device.
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34#include "apue.h"
#ifdef SOLARIS
#include <sys/mkdev.h>
#endif
int main(int argc, char *argv[])
{
int i;
struct stat buf;
for (i = 1; i < argc; i++)
{
printf("%s: ", argv[i]);
if (stat(argv[i], &buf) < 0)
{
err_ret("stat error");
continue;
}
printf("dev = %d/%d", major(buf.st_dev), minor(buf.st_dev));
if (S_ISCHR(buf.st_mode) || S_ISBLK(buf.st_mode))
{
printf(" (%s) rdev = %d/%d",
(S_ISCHR(buf.st_mode)) ? "character" : "block",
major(buf.st_rdev), minor(buf.st_rdev));
}
printf(" ");
}
exit(0);
}
$ ./a.out / /home/sar /dev/tty[01]
/: dev = 3/3
/home/sar: dev = 3/4
/dev/tty0: dev = 0/7 (character) rdev = 4/0
/dev/tty1: dev = 0/7 (character) rdev = 4/1
$ mount which directories are mounted on which devices?
/dev/hda3 on / type ext2 (rw,noatime)
/dev/hda4 on /home type ext2 (rw,noatime)
$ ls -lL /dev/tty[01] /dev/hda[34]
brw------- 1 root 3, 3 Dec 31 1969 /dev/hda3
brw------- 1 root 3, 4 Dec 31 1969 /dev/hda4
crw------- 1 root 4, 0 Dec 31 1969 /dev/tty0
crw------- 1 root 4, 1 Jan 18 15:36 /dev/tty1
Note that the filenames and i-nodes for the two terminal devices (st_dev) are on device 0/7 the devfs pseudo file system, which implements the /dev but that their actual device numbers are 4/0 and 4/1.
参考：《APUE》