statx(2) System Calls Manual statx(2)

statx - get file status (extended)

Standard C library (libc, -lc)

#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);

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.)

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:

If pathname begins with a slash, then it is an absolute pathname that identifies the target file. In this case, dirfd is ignored.
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.
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.)
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:

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.
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.
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:

Do whatever stat(2) does. This is the default and is very much filesystem-specific.
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.
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 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:

The "preferred" block size for efficient filesystem I/O. (Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.)
Further status information about the file (see below for more information).
The number of hard links on a file.
This field contains the user ID of the owner of the file.
This field contains the ID of the group owner of the file.
The file type and mode. See inode(7) for details.
The inode number of the file.
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.
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.)
A mask indicating which bits in stx_attributes are supported by the VFS and the filesystem.
The file's last access timestamp.
The file's creation timestamp.
The file's last status change timestamp.
The file's last modification timestamp.
The device on which this file (inode) resides.
The device that this file (inode) represents if the file is of block or character device type.
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.
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.
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).

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:

The file is compressed by the filesystem and may take extra resources to access.
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).
The file can only be opened in append mode for writing. Random access writing is not permitted. See chattr(1).
File is not a candidate for backup when a backup program such as dump(8) is run. See chattr(1).
A key is required for the file to be encrypted by the filesystem.
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).
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.
The file is the root of a mount.

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.

Search permission is denied for one of the directories in the path prefix of pathname. (See also path_resolution(7).)
pathname is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.
pathname or statxbuf is NULL or points to a location outside the process's accessible address space.
Invalid flag specified in flags.
Reserved flag specified in mask. (Currently, there is one such flag, designated by the constant STATX__RESERVED, with the value 0x80000000U.)
Too many symbolic links encountered while traversing the pathname.
pathname is too long.
A component of pathname does not exist, or pathname is an empty string and AT_EMPTY_PATH was not specified in flags.
Out of memory (i.e., kernel memory).
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.

Linux.

Linux 4.11, glibc 2.28.

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), symlink(7)

2023-10-31 Linux man-pages 6.7