faccessat - 文件相对于一个目录文件描述符的更改权限
<unistd.h> int faccessat(int dirfd, const char *path, int mode ", int " flags );
The faccessat() system call operates in exactly the same way as access(2), except for the differences described in this manual page.
If the pathname given in path is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by access(2) for a relative pathname).
If the pathname given in path is relative and dirfd is the special value AT_FDCWD, thenpath is interpreted relative to the current working directory of the calling process (likeaccess(2)).
If the pathname given in path is absolute, then dirfd is ignored.
flags is constructed by ORing together zero or more of the following values:
|Perform access checks using the effective user and group IDs. By default, faccessat() uses the effective IDs (like access(2)).|
|If path is a symbolic link, do not dereference it: instead return information about the link itself.|
On success, faccessat() returns 0. On error, -1 is returned and errno is set to indicate the error.
The same errors that occur for access(2) can also occur for faccessat(). The following additional errors can occur for faccessat():
|EBADF||dirfd is not a valid file descriptor.|
|EINVAL||Invalid flag specified in flags.|
|ENOTDIR||path is a relative path and dirfd is a file descriptor referring to a file other than a directory.|
See openat(2) for an explanation of the need for faccessat().
The AT_EACCESS and AT_SYMLINK_NOFOLLOW flags are actually implemented within the glibc wrapper function for faccessat(). If either of these flags are specified, then the wrapper function employs fstatat(2) to determine access permissions.
faccessat() 加入到Linux 的 kernel 2.6.16.
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