rename.2: glibc 2.28 adds library support for renameat2()

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.\" Copyright (c) 2017 David Howells <dhowells@redhat.com>
.\"
.\" Derived from the stat.2 manual page:
.\"   Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"   Parts Copyright (c) 1995 Nicolai Langfeldt (janl@ifi.uio.no), 1/1/95
.\"   and Copyright (c) 2006, 2007, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
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.TH STATX 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
statx \- get file status (extended)
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/stat.h>
.B #include <unistd.h>
.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
.PP
.BI "int statx(int " dirfd ", const char *" pathname ", int " flags ","
.BI "          unsigned int " mask ", struct statx *" statxbuf );
.fi
.PP
.IR Note :
There is no glibc wrapper for
.BR statx ();
see NOTES.
.SH DESCRIPTION
.PP
This function returns information about a file, storing it in the buffer
pointed to by
.IR statxbuf .
The returned buffer is a structure of the following type:
.PP
.in +4n
.EX
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 */
};
.EE
.in
.PP
The file timestamps are structures of the following type:
.PP
.in +4n
.EX
struct statx_timestamp {
    __s64 tv_sec;    /* Seconds since the Epoch (UNIX time) */
    __u32 tv_nsec;   /* Nanoseconds since tv_sec */
};
.EE
.in
.PP
(Note that reserved space and padding is omitted.)
.SS
Invoking \fBstatx\fR():
.PP
To access a file's status, no permissions are required on the file itself,
but in the case of
.BR statx ()
with a pathname,
execute (search) permission is required on all of the directories in
.I pathname
that lead to the file.
.PP
.BR statx ()
uses
.IR pathname ,
.IR dirfd ,
and
.IR flags
to identify the target file in one of the following ways:
.TP
An absolute pathname
If
.I pathname
begins with a slash,
then it is an absolute pathname that identifies the target file.
In this case,
.I dirfd
is ignored.
.TP
A relative pathname
If
.I pathname
is a string that begins with a character other than a slash and
.IR dirfd
is
.BR AT_FDCWD ,
then
.I pathname
is a relative pathname that is interpreted relative to the process's
current working directory.
.TP
A directory-relative pathname
If
.I pathname
is a string that begins with a character other than a slash and
.I dirfd
is a file descriptor that refers to a directory, then
.I pathname
is a relative pathname that is interpreted relative to the directory
referred to by
.IR dirfd .
.TP
By file descriptor
If
.IR pathname
is an empty string and the
.B AT_EMPTY_PATH
flag is specified in
.IR flags
(see below),
then the target file is the one referred to by the file descriptor
.IR dirfd .
.PP
.I flags
can be used to influence a pathname-based lookup.
A value for
.I flags
is constructed by ORing together zero or more of the following constants:
.TP
.BR AT_EMPTY_PATH
.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
If
.I pathname
is an empty string, operate on the file referred to by
.IR dirfd
(which may have been obtained using the
.BR open (2)
.B O_PATH
flag).
In this case,
.I dirfd
can refer to any type of file, not just a directory.
.IP
If
.I dirfd
is
.BR AT_FDCWD ,
the call operates on the current working directory.
.IP
This flag is Linux-specific; define
.B _GNU_SOURCE
.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
to obtain its definition.
.TP
.BR AT_NO_AUTOMOUNT
Don't automount the terminal ("basename") component of
.I 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
.B AT_NO_AUTOMOUNT
flag has no effect if the mount point has already been mounted over.
This flag is Linux-specific; define
.B _GNU_SOURCE
.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
to obtain its definition.
.TP
.B AT_SYMLINK_NOFOLLOW
If
.I pathname
is a symbolic link, do not dereference it:
instead return information about the link itself, like
.BR lstat (2).
.PP
.I 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:
.TP
.B AT_STATX_SYNC_AS_STAT
Do whatever
.BR stat (2)
does.
This is the default and is very much filesystem-specific.
.TP
.B 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.
.TP
.B 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.
.PP
The
.I mask
argument to
.BR statx ()
is used to tell the kernel which fields the caller is interested in.
.I mask
is an ORed combination of the following constants:
.PP
.in +4n
.TS
lB l.
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	[All currently available fields]
.TE
.in
.PP
Note that the kernel does
.I not
reject values in
.I mask
other than the above.
Instead, it simply informs the caller which values are supported
by this kernel and filesystem via the
.I statx.stx_mask
field.
Therefore,
.I "do not"
simply set
.I mask
to
.B UINT_MAX
(all bits set),
as one or more bits may, in the future, be used to specify an
extension to the buffer.
.SS
The returned information
.PP
The status information for the target file is returned in the
.I statx
structure pointed to by
.IR statxbuf .
Included in this is
.I stx_mask
which indicates what other information has been returned.
.I stx_mask
has the same format as the
.I mask
argument and bits are set in it to indicate
which fields have been filled in.
.PP
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,
.I stx_mask
will not be equal
.IR mask .
.PP
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
.I 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).
.PP
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
.IR stx_mask .
.PP
.\" Background: inode attributes are modified with i_mutex held, but
.\" read by stat() without taking the mutex.
.IR Note :
for performance and simplicity reasons, different fields in the
.I statx
structure may contain state information from different moments
during the execution of the system call.
For example, if
.IR stx_mode
or
.IR stx_uid
is changed by another process by calling
.BR chmod (2)
or
.BR chown (2),
.BR stat ()
might return the old
.I stx_mode
together with the new
.IR stx_uid ,
or the old
.I stx_uid
together with the new
.IR stx_mode .
.PP
Apart from
.I stx_mask
(which is described above), the fields in the
.I statx
structure are:
.TP
.I 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.)
.TP
.I stx_attributes
Further status information about the file (see below for more information).
.TP
.I stx_nlink
The number of hard links on a file.
.TP
.I stx_uid
This field contains the user ID of the owner of the file.
.TP
.I stx_gid
This field contains the ID of the group owner of the file.
.TP
.I stx_mode
The file type and mode.
See
.BR inode (7)
for details.
.TP
.I stx_ino
The inode number of the file.
.TP
.I 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.
.TP
.I stx_blocks
The number of blocks allocated to the file on the medium, in 512-byte units.
(This may be smaller than
.IR stx_size /512
when the file has holes.)
.TP
.I stx_attributes_mask
A mask indicating which bits in
.IR stx_attributes
are supported by the VFS and the filesystem.
.TP
.I stx_atime
The file's last access timestamp.
.TP
.I stx_btime
The file's creation timestamp.
.TP
.I stx_ctime
The file's last status change timestamp.
.TP
.I stx_mtime
The file's last modification timestamp.
.TP
.IR stx_dev_major " and "  stx_dev_minor
The device on which this file (inode) resides.
.TP
.IR stx_rdev_major " and "  stx_rdev_minor
The device that this file (inode) represents if the file is of block or
character device type.
.PP
For further information on the above fields, see
.BR inode (7).
.\"
.SS File attributes
.PP
The
.I 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
.I stx_attributes_mask
has no usable value here.
The bits in
.I stx_attributes_mask
correspond bit-by-bit to
.IR stx_attributes .
.PP
The flags are as follows:
.TP
.B STATX_ATTR_COMPRESSED
The file is compressed by the filesystem and may take extra resources
to access.
.TP
.B 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
.BR chattr (1).
.TP
.B STATX_ATTR_APPEND
The file can only be opened in append mode for writing.
Random access writing
is not permitted.
See
.BR chattr (1).
.TP
.B STATX_ATTR_NODUMP
File is not a candidate for backup when a backup program such as
.BR dump (8)
is run.
See
.BR chattr (1).
.TP
.B STATX_ATTR_ENCRYPTED
A key is required for the file to be encrypted by the filesystem.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Search permission is denied for one of the directories
in the path prefix of
.IR pathname .
(See also
.BR path_resolution (7).)
.TP
.B EBADF
.I dirfd
is not a valid open file descriptor.
.TP
.B EFAULT
.I pathname
or
.I statxbuf
is NULL or points to a location outside the process's
accessible address space.
.TP
.B EINVAL
Invalid flag specified in
.IR flags .
.TP
.B EINVAL
Reserved flag specified in
.IR mask .
.TP
.B ELOOP
Too many symbolic links encountered while traversing the pathname.
.TP
.B ENAMETOOLONG
.I pathname
is too long.
.TP
.B ENOENT
A component of
.I pathname
does not exist, or
.I pathname
is an empty string and
.B AT_EMPTY_PATH
was not specified in
.IR flags .
.TP
.B ENOMEM
Out of memory (i.e., kernel memory).
.TP
.B ENOTDIR
A component of the path prefix of
.I pathname
is not a directory or
.I pathname
is relative and
.I dirfd
is a file descriptor referring to a file other than a directory.
.SH VERSIONS
.BR statx ()
was added to Linux in kernel 4.11.
.SH CONFORMING TO
.BR statx ()
is Linux-specific.
.SH NOTES
Glibc does not (yet) provide a wrapper for the
.BR statx ()
system call; call it using
.BR syscall (2).
.SH SEE ALSO
.BR ls (1),
.BR stat (1),
.BR access (2),
.BR chmod (2),
.BR chown (2),
.BR readlink (2),
.BR stat (2),
.BR utime (2),
.BR capabilities (7),
.BR inode (7),
.BR symlink (7)