文件的属性
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：
|
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 |
/*************************************************************************
> 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\n"); break; case S_IFLNK: printf("symbolic link\n"); break; case S_IFREG: printf("regular file\n"); break; case S_IFBLK: printf("block device\n"); flag = 1; break; case S_IFDIR: printf("directory\n"); break; case S_IFCHR: printf("character device\n"); flag = 1; break; case S_IFIFO: printf("FIFO\n"); break; default: printf("unknown file type\n"); 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] = '\0'; } int main(int argc, char *argv[]) { if (argc != 2) { fprintf(stderr, "Usage %s file\n", argv[0]); exit(EXIT_FAILURE); } printf("Filename:%s\n", argv[1]); struct stat sbuf; if (lstat(argv[1], &sbuf) == -1) ERR_EXIT("stat error"); printf("file in Dev number:major %d, minor %d\n", MAJOR(sbuf.st_dev), MINOR(sbuf.st_dev)); printf("File inode:%d\n", (int) sbuf.st_ino); if (filetype(&sbuf)) { printf("Device number:major %d, minor %d\n", MAJOR(sbuf.st_rdev), MINOR(sbuf.st_rdev)); } char perm[11] = {0}; fileperm(&sbuf, perm); printf("File permission bits=%o %s\n", 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。
-
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.
-
Only character special files and block special files have an st_rdev value. This value contains the device number for the actual device.
C++ Code1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
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("\n");
}
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》
