Ubuntu Manpage: statx - get file status (extended)

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 following 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 itself, but in the case
of statx() with a pathname, execute (search) permission 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 directory.

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 explanation 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 directories to prevent
mass-automounting of a directory of automount points.

All of stat(2), lstat(2), and fstatat(2) act as though AT_NO_AUTOMOUNT 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 kernel 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 information 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 requested and may fail
to return fields that were requested, depending on what the backing filesystem supports.
(Fields that are given values despite 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 corresponding 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 purposes 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. (Writing 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 information).

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 pathname 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 direct I/O (O_DIRECT)
on this file, or 0 if direct I/O is not supported 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 regular 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 segment lengths for
direct I/O (O_DIRECT) on this file, or 0 if direct 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 additional 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 resources 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 attempts 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 instructions 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 bypass 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.

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 pathname.

       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.

VERSIONS

       statx() was added in Linux 4.11; library support was added in glibc 2.28.

STANDARDS

       statx() is Linux-specific.