получить статус файла (расширенный) (get file status (extended))
Имя (Name)
statx - get file status (extended)
Синопсис (Synopsis)
#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);
Описание (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 */
};
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.
This flag is Linux-specific; define _GNU_SOURCE to obtain
its definition.
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 can be used in tools that scan directories to
prevent mass-automounting of a directory of automount
points. The AT_NO_AUTOMOUNT flag has no effect if the
mount point has already been mounted over. This flag is
Linux-specific; define _GNU_SOURCE to obtain its
definition.
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_MNT_ID Want stx_mnt_id (since Linux 5.8)
STATX_ALL [All currently available fields]
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.
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.
