linux系统编程之文件与I/O（四）：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：
/*************************************************************************
> 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. #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/tty1Note 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.
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