From Linux Man Pages
fstatat - get file status relative to a directory file descriptor
SYNOPSIS
#include <sys/stat.h>
int fstatat(int dirfd, const char *pathname, struct stat *buf, int flags);
DESCRIPTION
The fstatat() system call operates in exactly the same way as stat(2), except for the differences described in
this manual page.
If the pathname given in pathname 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 stat(2) for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted relative to the
current working directory of the calling process (like stat(2)).
If pathname is absolute, then dirfd is ignored.
flags can either be 0, or include the following flag:
AT_SYMLINK_NOFOLLOW
If pathname is a symbolic link, do not dereference it: instead return information about the link itself,
like lstat(2). (By default, fstatat() dereferences symbolic links, like stat(2).)
RETURN VALUE
On success, fstatat() returns 0. On error, -1 is returned and errno is set to indicate the error.
ERRORS
The same errors that occur for stat(2) can also occur for fstatat(). The following additional errors can occur
for fstatat():
EBADF dirfd is not a valid file descriptor.
EINVAL Invalid flag specified in flags.
ENOTDIR
pathname is relative and dirfd is a file descriptor referring to a file other than a directory.
NOTES
See openat(2) for an explanation of the need for fstatat().
CONFORMING TO
This system call is non-standard but is proposed for inclusion in a future revision of POSIX.1. A similar system
call exists on Solaris.
VERSIONS
fstatat() was added to Linux in kernel 2.6.16.
RELATED
openat(2), path_resolution(2), stat(2)
CATEGORY