stat结构体中的st_mode理解

最新推荐文章于 2022-12-17 17:01:52 发布

原创最新推荐文章于 2022-12-17 17:01:52 发布 · 2.2k 阅读

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本文探讨了apue第四章4-12实例中关于statbuf.st_mode的使用，尤其是表达式`statbuf.st_mode & ~S_IXGRP`的含义。作者指出，对于这个操作的疑惑可以通过查阅 `/usr/include/linux/stat.h`来解答。同时，文章推荐了两篇来自优快云博主的详细解释链接，帮助读者深入理解。

apue第四章4-12实例changemod.c

#include "apue.h"

int
main(void)
{
    struct stat     statbuf;

    /* turn on set-group-ID and turn off group-execute */

    if (stat("foo", &statbuf) < 0)
        err_sys("stat error for foo");
    if (chmod("foo", (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
        err_sys("chmod error for foo");
    /* set absolute mode to "rw-r--r--" */

    if (chmod("bar", S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
        err_sys("chmod error for bar");

    exit(0);
}

对statbuf.st_mode & ~S_IXGRP这个操作有些疑惑
查看/usr/include/linux/stat.h

#define S_IFMT  00170000
#define S_IFSOCK 0140000
#define S_IFLNK  0120000
#define S_IFREG  0100000
#define S_IFBLK  0060000
#define S_IFDIR  0040000
#define S_IFCHR  0020000
#define S_IFIFO  0010000
#define S_ISUID  0004000
#define S_ISGID  0002000
#define S_ISVTX  0001000

#define S_ISLNK(m)  (((m) & S_IFMT) == S_IFLNK)
#define S_ISREG(m)  (((m) & S_IFMT) == S_IFREG)
#define S_ISDIR(m)  (((m) & S_IFMT) == S_IFDIR)
#define S_ISCHR(m)  (((m) & S_IFMT) == S_IFCHR)
#define S_ISBLK(m)  (((m) & S_IFMT) == S_IFBLK)
#define S_ISFIFO(m) (((m) & S_IFMT) == S_IFIFO)
#define S_ISSOCK(m) (((m) & S_IFMT) == S_IFSOCK)

#define S_IRWXU 00700
#define S_IRUSR 00400
#define S_IWUSR 00200
#define S_IXUSR 00100

#define S_IRWXG 00070
#define S_IRGRP 00040
#define S_IWGRP 00020
#define S_IXGRP 00010

#define S_IRWXO 00007
#define S_IROTH 00004
#define S_IWOTH 00002
#define S_IXOTH 00001