fstatat#

Synopsis#

#include <fcntl.h>

#include <sys/stat.h>

int fstatat(int fd, const char *restrict path,

struct stat *restrict buf, int flag);

int lstat(const char *restrict path, struct stat *restrict buf);

int stat(const char *restrict path, struct stat *restrict buf);

Status#

Partially implemented

Conformance#

IEEE Std 1003.1-2017

Description#

The purpose is to get file status. The stat() function shall obtain information about the named file and write it to the area pointed to by the buf argument. The path argument points to a path name naming a file. Read, write, or execute permission of the named file is not required. An implementation that provides additional or alternate file access control mechanisms may, under implementation-defined conditions, cause stat() to fail. In particular, the system may deny the existence of the file specified by path.

If the named file is a symbolic link, the stat() function shall continue path name resolution using the contents of the symbolic link, and shall return information pertaining to the resulting file if the file exists.

The buf argument is a pointer to a stat structure, as defined in the <sys/stat.h> header, into which information is placed concerning the file.

The stat() function shall update any time-related fields, before writing into the stat structure. If the named file is a shared memory object, the implementation shall update in the stat structure pointed to by the buf argument the st_uid, st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be valid. The implementation may update other fields and flags.

If the named file is a typed memory object, the implementation shall update in the stat structure pointed to by the buf argument the st_uid, st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be valid. The implementation may update other fields and flags.

For all other file types defined in this volume of POSIX.1-2017, the structure members st_mode, st_ino, st_dev, st_uid, st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and the value of the member st_nlink shall be set to the number of links to the file.

The lstat() function shall be equivalent to stat(), except when path refers to a symbolic link. In that case lstat() shall return information about the link, while stat() shall return information about the file the link references.

For symbolic links, the st_mode member shall contain meaningful information when used with the file type macros. The file mode bits in st_mode are unspecified. The structure members st_ino, st_dev, st_uid, st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and the value of the st_nlink member shall be set to the number of (hard) links to the symbolic link. The value of the st_size member shall be set to the length of the path name contained in the symbolic link not including any terminating null byte.

The fstatat() function shall be equivalent to the stat() or lstat() function, depending on the value of flag (see below), except in the case where path specifies a relative path. In this case the status shall be retrieved from a file relative to the directory associated with the file descriptor fd instead of the current working directory. If the access mode of the open file description associated with the file descriptor is not O_SEARCH, the function shall check whether directory searches are permitted using the current permissions of the directory underlying the file descriptor. If the access mode is O_SEARCH, the function shall not perform the check.

Values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

AT_SYMLINK_NOFOLLOW

If path names a symbolic link, the status of the symbolic link is returned.

If fstatat() is passed the special value AT_FDCWD in the fd parameter, the current working directory shall be used and the behavior shall be identical to a call to stat() or lstat() respectively, depending on whether the AT_SYMLINK_NOFOLLOW bit is set in flag.

Return value#

Upon successful completion, these functions shall return 0. Otherwise, these functions shall return -1 and set errno to indicate the error.

Errors#

These functions shall fail if:

EACCES - Search permission is denied for a component of the path prefix.
EIO - An error occurred while reading from the file system.
ELOOP - A loop exists in symbolic links encountered during resolution of the path argument.
ENAMETOOLONG - The length of a component of a path name is longer than NAME_MAX.
ENOENT - A component of path does not name an existing file or path is an empty string.
ENOTDIR - A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory, or the path argument contains at least one non- / character and ends with one or more trailing / characters and the last path name component names an existing file that is neither a directory nor a symbolic link to a directory.
EOVERFLOW - The file size in bytes or the number of blocks allocated to the file or the file serial number cannot be represented correctly in the structure pointed to by buf.

The fstatat() function shall fail if:

EACCES - The access mode of the open file description associated with fd is not O_SEARCH and the permissions of the directory underlying fd do not permit directory searches.
EBADF - The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching.
ENOTDIR - The path argument is not an absolute path and fd is a file descriptor associated with a non-directory file.

These functions may fail if:

ELOOP - More than SYMLOOP_MAX symbolic links were encountered during resolution of the path argument.
ENAMETOOLONG - The length of a path name exceeds PATH_MAX, or path name resolution of a symbolic link produced an intermediate result with a length that exceeds PATH_MAX.
EOVERFLOW - A value to be stored would overflow one of the members of the stat structure.

The fstatat() function may fail if:

EINVAL - The value of the flag argument is not valid.

Tests#

Untested

Known bugs#

None