statx(2) System Calls Manual statx(2)
NAME
statx - get file status (extended)
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
int statx(int dirfd, const char *restrict pathname, int flags,
unsigned int mask, struct statx *restrict statxbuf);
DESCRIPTION
This function returns information about a file, storing it in the buffer
pointed to by statxbuf. The returned buffer is a structure of the fol-
lowing type:
struct statx {
__u32 stx_mask; /* Mask of bits indicating
filled fields */
__u32 stx_blksize; /* Block size for filesystem I/O */
__u64 stx_attributes; /* Extra file attribute indicators */
__u32 stx_nlink; /* Number of hard links */
__u32 stx_uid; /* User ID of owner */
__u32 stx_gid; /* Group ID of owner */
__u16 stx_mode; /* File type and mode */
__u64 stx_ino; /* Inode number */
__u64 stx_size; /* Total size in bytes */
__u64 stx_blocks; /* Number of 512B blocks allocated */
__u64 stx_attributes_mask;
/* Mask to show what's supported
in stx_attributes */
/* The following fields are file timestamps */
struct statx_timestamp stx_atime; /* Last access */
struct statx_timestamp stx_btime; /* Creation */
struct statx_timestamp stx_ctime; /* Last status change */
struct statx_timestamp stx_mtime; /* Last modification */
/* If this file represents a device, then the next two
fields contain the ID of the device */
__u32 stx_rdev_major; /* Major ID */
__u32 stx_rdev_minor; /* Minor ID */
/* The next two fields contain the ID of the device
containing the filesystem where the file resides */
__u32 stx_dev_major; /* Major ID */
__u32 stx_dev_minor; /* Minor ID */
__u64 stx_mnt_id; /* Mount ID */
/* Direct I/O alignment restrictions */
__u32 stx_dio_mem_align;
__u32 stx_dio_offset_align;
};
The file timestamps are structures of the following type:
struct statx_timestamp {
__s64 tv_sec; /* Seconds since the Epoch (UNIX time) */
__u32 tv_nsec; /* Nanoseconds since tv_sec */
};
(Note that reserved space and padding is omitted.)
Invoking statx():
To access a file's status, no permissions are required on the file it-
self, but in the case of statx() with a pathname, execute (search) per-
mission is required on all of the directories in pathname that lead to
the file.
statx() uses pathname, dirfd, and flags to identify the target file in
one of the following ways:
An absolute pathname
If pathname begins with a slash, then it is an absolute pathname
that identifies the target file. In this case, dirfd is ignored.
A relative pathname
If pathname is a string that begins with a character other than a
slash and dirfd is AT_FDCWD, then pathname is a relative pathname
that is interpreted relative to the process's current working di-
rectory.
A directory-relative pathname
If pathname is a string that begins with a character other than a
slash and dirfd is a file descriptor that refers to a directory,
then pathname is a relative pathname that is interpreted relative
to the directory referred to by dirfd. (See openat(2) for an ex-
planation of why this is useful.)
By file descriptor
If pathname is an empty string and the AT_EMPTY_PATH flag is
specified in flags (see below), then the target file is the one
referred to by the file descriptor dirfd.
flags can be used to influence a pathname-based lookup. A value for
flags is constructed by ORing together zero or more of the following
constants:
AT_EMPTY_PATH
If pathname is an empty string, operate on the file referred to
by dirfd (which may have been obtained using the open(2) O_PATH
flag). In this case, dirfd can refer to any type of file, not
just a directory.
If dirfd is AT_FDCWD, the call operates on the current working
directory.
AT_NO_AUTOMOUNT
Don't automount the terminal ("basename") component of pathname
if it is a directory that is an automount point. This allows the
caller to gather attributes of an automount point (rather than
the location it would mount). This flag has no effect if the
mount point has already been mounted over.
The AT_NO_AUTOMOUNT flag can be used in tools that scan directo-
ries to prevent mass-automounting of a directory of automount
points.
All of stat(2), lstat(2), and fstatat(2) act as though AT_NO_AU-
TOMOUNT was set.
AT_SYMLINK_NOFOLLOW
If pathname is a symbolic link, do not dereference it: instead
return information about the link itself, like lstat(2).
flags can also be used to control what sort of synchronization the ker-
nel will do when querying a file on a remote filesystem. This is done
by ORing in one of the following values:
AT_STATX_SYNC_AS_STAT
Do whatever stat(2) does. This is the default and is very much
filesystem-specific.
AT_STATX_FORCE_SYNC
Force the attributes to be synchronized with the server. This
may require that a network filesystem perform a data writeback to
get the timestamps correct.
AT_STATX_DONT_SYNC
Don't synchronize anything, but rather just take whatever the
system has cached if possible. This may mean that the informa-
tion returned is approximate, but, on a network filesystem, it
may not involve a round trip to the server - even if no lease is
held.
The mask argument to statx() is used to tell the kernel which fields the
caller is interested in. mask is an ORed combination of the following
constants:
STATX_TYPE Want stx_mode & S_IFMT
STATX_MODE Want stx_mode & ~S_IFMT
STATX_NLINK Want stx_nlink
STATX_UID Want stx_uid
STATX_GID Want stx_gid
STATX_ATIME Want stx_atime
STATX_MTIME Want stx_mtime
STATX_CTIME Want stx_ctime
STATX_INO Want stx_ino
STATX_SIZE Want stx_size
STATX_BLOCKS Want stx_blocks
STATX_BASIC_STATS [All of the above]
STATX_BTIME Want stx_btime
STATX_ALL The same as STATX_BASIC_STATS | STATX_BTIME.
It is deprecated and should not be used.
STATX_MNT_ID Want stx_mnt_id (since Linux 5.8)
STATX_DIOALIGN Want stx_dio_mem_align and stx_dio_offset_align
(since Linux 6.1; support varies by filesystem)
Note that, in general, the kernel does not reject values in mask other
than the above. (For an exception, see EINVAL in errors.) Instead, it
simply informs the caller which values are supported by this kernel and
filesystem via the statx.stx_mask field. Therefore, do not simply set
mask to UINT_MAX (all bits set), as one or more bits may, in the future,
be used to specify an extension to the buffer.
The returned information
The status information for the target file is returned in the statx
structure pointed to by statxbuf. Included in this is stx_mask which
indicates what other information has been returned. stx_mask has the
same format as the mask argument and bits are set in it to indicate
which fields have been filled in.
It should be noted that the kernel may return fields that weren't re-
quested and may fail to return fields that were requested, depending on
what the backing filesystem supports. (Fields that are given values de-
spite being unrequested can just be ignored.) In either case, stx_mask
will not be equal mask.
If a filesystem does not support a field or if it has an unrepresentable
value (for instance, a file with an exotic type), then the mask bit cor-
responding to that field will be cleared in stx_mask even if the user
asked for it and a dummy value will be filled in for compatibility pur-
poses if one is available (e.g., a dummy UID and GID may be specified to
mount under some circumstances).
A filesystem may also fill in fields that the caller didn't ask for if
it has values for them available and the information is available at no
extra cost. If this happens, the corresponding bits will be set in
stx_mask.
Note: for performance and simplicity reasons, different fields in the
statx structure may contain state information from different moments
during the execution of the system call. For example, if stx_mode or
stx_uid is changed by another process by calling chmod(2) or chown(2),
stat() might return the old stx_mode together with the new stx_uid, or
the old stx_uid together with the new stx_mode.
Apart from stx_mask (which is described above), the fields in the statx
structure are:
stx_blksize
The "preferred" block size for efficient filesystem I/O. (Writ-
ing to a file in smaller chunks may cause an inefficient read-
modify-rewrite.)
stx_attributes
Further status information about the file (see below for more in-
formation).
stx_nlink
The number of hard links on a file.
stx_uid
This field contains the user ID of the owner of the file.
stx_gid
This field contains the ID of the group owner of the file.
stx_mode
The file type and mode. See inode(7) for details.
stx_ino
The inode number of the file.
stx_size
The size of the file (if it is a regular file or a symbolic link)
in bytes. The size of a symbolic link is the length of the path-
name it contains, without a terminating null byte.
stx_blocks
The number of blocks allocated to the file on the medium, in
512-byte units. (This may be smaller than stx_size/512 when the
file has holes.)
stx_attributes_mask
A mask indicating which bits in stx_attributes are supported by
the VFS and the filesystem.
stx_atime
The file's last access timestamp.
stx_btime
The file's creation timestamp.
stx_ctime
The file's last status change timestamp.
stx_mtime
The file's last modification timestamp.
stx_dev_major and stx_dev_minor
The device on which this file (inode) resides.
stx_rdev_major and stx_rdev_minor
The device that this file (inode) represents if the file is of
block or character device type.
stx_mnt_id
The mount ID of the mount containing the file. This is the same
number reported by name_to_handle_at(2) and corresponds to the
number in the first field in one of the records in
/proc/self/mountinfo.
stx_dio_mem_align
The alignment (in bytes) required for user memory buffers for di-
rect I/O (O_DIRECT) on this file, or 0 if direct I/O is not sup-
ported on this file.
STATX_DIOALIGN (stx_dio_mem_align and stx_dio_offset_align) is
supported on block devices since Linux 6.1. The support on regu-
lar files varies by filesystem; it is supported by ext4, f2fs,
and xfs since Linux 6.1.
stx_dio_offset_align
The alignment (in bytes) required for file offsets and I/O seg-
ment lengths for direct I/O (O_DIRECT) on this file, or 0 if di-
rect I/O is not supported on this file. This will only be
nonzero if stx_dio_mem_align is nonzero, and vice versa.
For further information on the above fields, see inode(7).
File attributes
The stx_attributes field contains a set of ORed flags that indicate ad-
ditional attributes of the file. Note that any attribute that is not
indicated as supported by stx_attributes_mask has no usable value here.
The bits in stx_attributes_mask correspond bit-by-bit to stx_attributes.
The flags are as follows:
STATX_ATTR_COMPRESSED
The file is compressed by the filesystem and may take extra re-
sources to access.
STATX_ATTR_IMMUTABLE
The file cannot be modified: it cannot be deleted or renamed, no
hard links can be created to this file and no data can be written
to it. See chattr(1).
STATX_ATTR_APPEND
The file can only be opened in append mode for writing. Random
access writing is not permitted. See chattr(1).
STATX_ATTR_NODUMP
File is not a candidate for backup when a backup program such as
dump(8) is run. See chattr(1).
STATX_ATTR_ENCRYPTED
A key is required for the file to be encrypted by the filesystem.
STATX_ATTR_VERITY (since Linux 5.5)
The file has fs-verity enabled. It cannot be written to, and all
reads from it will be verified against a cryptographic hash that
covers the entire file (e.g., via a Merkle tree).
STATX_ATTR_DAX (since Linux 5.8)
The file is in the DAX (cpu direct access) state. DAX state at-
tempts to minimize software cache effects for both I/O and memory
mappings of this file. It requires a file system which has been
configured to support DAX.
DAX generally assumes all accesses are via CPU load / store in-
structions which can minimize overhead for small accesses, but
may adversely affect CPU utilization for large transfers.
File I/O is done directly to/from user-space buffers and memory
mapped I/O may be performed with direct memory mappings that by-
pass the kernel page cache.
While the DAX property tends to result in data being transferred
synchronously, it does not give the same guarantees as the O_SYNC
flag (see open(2)), where data and the necessary metadata are
transferred together.
A DAX file may support being mapped with the MAP_SYNC flag, which
enables a program to use CPU cache flush instructions to persist
CPU store operations without an explicit fsync(2). See mmap(2)
for more information.
STATX_ATTR_MOUNT_ROOT (since Linux 5.8)
The file is the root of a mount.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set to indicate the error.
ERRORS
EACCES Search permission is denied for one of the directories in the
path prefix of pathname. (See also path_resolution(7).)
EBADF pathname is relative but dirfd is neither AT_FDCWD nor a valid
file descriptor.
EFAULT pathname or statxbuf is NULL or points to a location outside the
process's accessible address space.
EINVAL Invalid flag specified in flags.
EINVAL Reserved flag specified in mask. (Currently, there is one such
flag, designated by the constant STATX__RESERVED, with the value
0x80000000U.)
ELOOP Too many symbolic links encountered while traversing the path-
name.
ENAMETOOLONG
pathname is too long.
ENOENT A component of pathname does not exist, or pathname is an empty
string and AT_EMPTY_PATH was not specified in flags.
ENOMEM Out of memory (i.e., kernel memory).
ENOTDIR
A component of the path prefix of pathname is not a directory or
pathname is relative and dirfd is a file descriptor referring to
a file other than a directory.
STANDARDS
Linux.
HISTORY
Linux 4.11, glibc 2.28.
SEE ALSO
ls(1), stat(1), access(2), chmod(2), chown(2), name_to_handle_at(2),
readlink(2), stat(2), utime(2), proc(5), capabilities(7), inode(7), sym-
link(7)
Linux man-pages 6.9.1 2024-05-02 statx(2)
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