man/man3/xfsctl.3

.TH XFSCTL 3
.SH NAME
xfsctl \- control XFS filesystems and individual files
.SH C SYNOPSIS
.B #include <xfs/xfs.h>
.HP
.BI "int\ xfsctl(const char *" path ", int " fd ", int " cmd ", void *" ptr );
.PP
.BI "int platform_test_xfs_fd(int " fd );
.br
.BI "int platform_test_xfs_path(const char *" path );
.SH DESCRIPTION
Some functionality specific to the XFS filesystem is accessible to
applications through platform-specific system call interfaces.
These operations can be divided into two sections \- operations
that operate on individual files, and operations that operate on
the filesystem itself. Care should be taken when issuing
.BR xfsctl ()
calls to ensure the target path and file descriptor (both must
be supplied) do indeed represent a file from an XFS filesystem.
The
.BR statfs (2)
and
.BR fstatfs (2)
system calls can be used to determine whether or not an arbitrary
path or file descriptor belong to an XFS filesystem.
These are not portable however, so the routines
.BR platform_test_xfs_fd ()
and
.BR platform_test_xfs_path ()
provide a platform-independent mechanism.
.SS File Operations
In order to effect an operation on an individual file, the pathname
and descriptor arguments passed to
.B xfsctl
identifies the file being operated on.
The final argument described below refers to the final argument of
.BR xfsctl .
All of the data structures and macros mentioned below are defined in the
.RI < xfs/xfs_fs.h >
header file.
.PP
.B XFS_IOC_ALLOCSP
.br
.B XFS_IOC_ALLOCSP64
.br
.B XFS_IOC_FREESP
.PD 0
.TP
.B XFS_IOC_FREESP64
Alter storage space associated with a section of the ordinary
file specified.  The section is specified by a variable of type
.BR xfs_flock64_t ,
pointed to by the final argument.
The data type
.B xfs_flock64_t
contains the following members:
.B l_whence
is 0, 1, or 2 to indicate that the relative offset
.B l_start
will be measured from the start of the file, the current position, or
the end of the file, respectively (i.e.,
.B l_start
is the offset from the position specified in
.BR l_whence ).
If the offset specified is before the current end of file, any data
previously written into this section is no longer accessible.
If the offset specified is beyond the current end of file, the file
is grown and filled with zeroes.
The
.B l_len
field is currently ignored, and should be set to zero.

.BR XFS_IOC_ALLOCSP ,
.BR XFS_IOC_ALLOCSP64 ,
.B XFS_IOC_FREESP
and
.B XFS_IOC_FREESP64
operations are all identical.

These ioctls are no longer supported as of Linux 5.17.

.TP
.B XFS_IOC_FSSETDM
Set the di_dmevmask and di_dmstate fields in an XFS on-disk inode.
The only legitimate values for these fields are those
previously returned in the
.B bs_dmevmask
and
.B bs_dmstate
fields of the bulkstat structure.
The data referred to by the final argument is a
.BR "struct fsdmidata" .
This structure's members are
.B fsd_dmevmask
and
.BR fsd_dmstate .
The di_dmevmask
field is set to the value in
.BR fsd_dmevmask .
The di_dmstate field is set to the value in
.BR fsd_dmstate .
This command is restricted to root or to processes with device
management capabilities.
Its sole purpose is to allow backup and restore programs to restore the
aforementioned critical on-disk inode fields.
This ioctl is not supported as of Linux 5.5.

.TP
.B XFS_IOC_DIOINFO
Get information required to perform direct I/O on the specified file
descriptor.
Direct I/O is performed directly to and from a user's data buffer.
Since the kernel's buffer cache is no longer between the two, the
user's data buffer must conform to the same type of constraints as
required for accessing a raw disk partition.
The final argument points to a variable of type
.BR "struct dioattr" ,
which contains the following members:
.B d_mem
is the memory alignment requirement of the user's data buffer.
.B d_miniosz
specifies block size, minimum I/O request size, and I/O alignment.
The size of all I/O requests must be a multiple of this amount and
the value of the seek pointer at the time of the I/O request must
also be an integer multiple of this amount.
.B d_maxiosz
is the maximum I/O request size which can be performed on the file
descriptor.
If an I/O request does not meet these constraints, the
.BR read (2)
or
.BR write (2)
will fail with EINVAL.
All I/O requests are kept consistent with any data brought into
the cache with an access through a non-direct I/O file descriptor.

.PP
.nf
.B XFS_IOC_FSGETXATTR
.B XFS_IOC_FSGETXATTRA
.fi
.PD 0
.TP
.B XFS_IOC_FSSETXATTR
See
.BR ioctl_xfs_fsgetxattr (2)
for more information.

.PP
.nf
.B XFS_IOC_GETBMAP
.B XFS_IOC_GETBMAPA
.fi
.PD 0
.TP
.B XFS_IOC_GETBMAPX
See
.BR ioctl_getbmap (2)
for more information.

.PP
.B XFS_IOC_RESVSP
.TP
.B XFS_IOC_RESVSP64
This command is used to allocate space to a file.
A range of bytes is specified using a pointer to a variable of type
.B xfs_flock64_t
in the final argument.
The blocks are allocated, but not zeroed, and the file size does not change.
If the XFS filesystem is configured to flag unwritten file extents,
performance will be negatively affected when writing to preallocated space,
since extra filesystem transactions are required to convert extent flags on
the range of the file written.
If
.BR xfs_info (8)
reports unwritten=1, then the filesystem was made to flag unwritten extents.

.PP
.B XFS_IOC_UNRESVSP
.TP
.B XFS_IOC_UNRESVSP64
This command is used to free space from a file.
A range of bytes is specified using a pointer to a variable of type
.B xfs_flock64_t
in the final argument.
Partial filesystem blocks are zeroed, and whole filesystem blocks are
removed from the file.  The file size does not change.

.TP
.B XFS_IOC_ZERO_RANGE
This command is used to convert a range of a file to zeros without issuing data
IO.
A range of bytes is specified using a pointer to a variable of type
.B xfs_flock64_t
in the final argument.
Blocks are preallocated for regions that span holes in the file, and the entire
range is converted to unwritten extents.
This operation is a fast method of overwriting any from the range specified
with zeros without removing any blocks or having to write zeros to disk.
Any subsequent read in the given range will return zeros until new data is
written.
This functionality requires filesystems to support unwritten extents.
If
.BR xfs_info (8)
reports unwritten=1, then the filesystem was made to flag unwritten extents.

.\" .TP
.\" .B XFS_IOC_GETBIOSIZE
.\" This command gets information about the preferred buffered I/O
.\" size used by the system when performing buffered I/O (e.g.
.\" standard Unix non-direct I/O) to and from the file.
.\" The information is passed back in a structure of type
.\" .B "struct biosize"
.\" pointed to by the final argument.
.\" biosize lengths are expressed in log base 2.
.\" That is if the value is 14, then the true size is 2^14 (2 raised to
.\" the 14th power).
.\" The
.\" .B biosz_read
.\" field will contain the current value used by the system when reading
.\" from the file.
.\" Except at the end-of-file, the system will read from the file in
.\" multiples of this length.
.\" The
.\" .B biosz_write
.\" field will contain the current value used by the system when writing
.\" to the file.
.\" Except at the end-of-file, the system will write to the file in
.\" multiples of this length.
.\" The
.\" .B dfl_biosz_read
.\" and
.\" .B dfl_biosz_write
.\" will be set to the system default values for the opened file.
.\" The
.\" .B biosz_flags
.\" field will be set to 1 if the current read or write value has been
.\" explicitly set.
.\"
.\" .TP
.\" .B XFS_IOC_SETBIOSIZE
.\" This command sets information about the preferred buffered I/O size
.\" used by the system when performing buffered I/O (e.g. standard Unix
.\" non-direct I/O) to and from the file.
.\" The information is passed in a structure of type
.\" .B "struct biosize"
.\" pointed to by the final argument.
.\" Using smaller preferred I/O sizes can result in performance
.\" improvements if the file is typically accessed using small
.\" synchronous I/Os or if only a small amount of the file is accessed
.\" using small random I/Os, resulting in little or no use of the
.\" additional data read in near the random I/Os.
.\"
.\" To explicitly set the preferred I/O sizes, the
.\" .B biosz_flags
.\" field should be set to zero and the
.\" .B biosz_read
.\" and
.\" .B biosz_write
.\" fields should be set to the log base 2 of the desired read and
.\" write lengths, respectively (e.g. 13 for 8K bytes, 14 for 16K
.\" bytes, 15 for 32K bytes, etc.).  Valid values are 13-16
.\" inclusive for machines with a 4K byte pagesize and 14-16 for
.\" machines with a 16K byte pagesize.  The specified read and
.\" write values must also result in lengths that are greater than
.\" or equal to the filesystem block size.
.\" The
.\" .B dfl_biosz_read
.\" and
.\" .B dfl_biosz_write
.\" fields are ignored.
.\"
.\" If biosizes have already been explicitly set due to a prior use
.\" of
.\" .BR XFS_IOC_SETBIOSIZE ,
.\" and the requested sizes are larger than the
.\" existing sizes, the
.\" .I xfsctl
.\" call will return successfully and the
.\" system will use the smaller of the two sizes.  However, if
.\" .B biosz_flags
.\" is set to 1, the system will use the new values
.\" regardless of whether the new sizes are larger or smaller than the old.
.\"
.\" To reset the biosize values to the defaults for the filesystem
.\" that the file resides in, the
.\" .B biosz_flags
.\" field should be set to 2.
.\" The remainder of the fields will be ignored in that case.
.\"
.\" Changes made by
.\" .B XFS_IOC_SETBIOSIZE
.\" are transient.
.\" The sizes are reset to the default values once the reference count on the
.\" file drops to zero (e.g. all open file descriptors to that file
.\" have been closed).
.\" See
.\" .I mount(8)
.\" for details on how to set the
.\" default biosize values for a filesystem.

.PP
.nf
.B XFS_IOC_PATH_TO_HANDLE
.B XFS_IOC_PATH_TO_FSHANDLE
.B XFS_IOC_FD_TO_HANDLE
.B XFS_IOC_OPEN_BY_HANDLE
.B XFS_IOC_READLINK_BY_HANDLE
.B XFS_IOC_ATTR_LIST_BY_HANDLE
.B XFS_IOC_ATTR_MULTI_BY_HANDLE
.fi
.PD 0
.TP
.B XFS_IOC_FSSETDM_BY_HANDLE
These are all interfaces that are used to implement various
.I libhandle
functions (see
.BR open_by_handle (3)).
They are all subject to change and should not be called directly
by applications.
XFS_IOC_FSSETDM_BY_HANDLE is not supported as of Linux 5.5.

.SS Filesystem Operations
In order to effect one of the following operations, the pathname
and descriptor arguments passed to
.BR xfsctl ()
can be any open file in the XFS filesystem in question.

.PP
.TP
.B XFS_IOC_FSINUMBERS
See
.BR ioctl_xfs_fsinumbers (2)
for more information.

.TP
.B XFS_IOC_FSGEOMETRY
See
.BR ioctl_xfs_fsgeometry (2)
for more information.

.TP
.B XFS_IOC_AG_GEOMETRY
See
.BR ioctl_xfs_ag_geometry (2)
for more information.

.TP
.BR XFS_IOC_FSBULKSTAT " or " XFS_IOC_FSBULKSTAT_SINGLE
See
.BR ioctl_xfs_fsbulkstat (2)
for more information.

.TP
.B XFS_IOC_SCRUB_METADATA
See
.BR ioctl_xfs_scrub_metadata (2)
for more information.

.TP
.B XFS_IOC_FSCOUNTS
See
.BR ioctl_xfs_fscounts (2)
for more information.

.TP
.nf
.B XFS_IOC_GET_RESBLKS
.fi
.TP
.B XFS_IOC_SET_RESBLKS
See
.BR ioctl_xfs_getresblks (2)
for more information.
Save yourself a lot of frustration and avoid these ioctls.

.TP
.B XFS_IOC_GOINGDOWN
See
.BR ioctl_xfs_goingdown (2)
for more information.

.PP
.nf
.B XFS_IOC_THAW
.B XFS_IOC_FREEZE
.B XFS_IOC_FSGROWFSDATA
.B XFS_IOC_FSGROWFSLOG
.fi
.TP
.B XFS_IOC_FSGROWFSRT
These interfaces are used to implement various filesystem internal
operations on XFS filesystems.
The remainder of these operations will not be described further
as they are not of general use to applications.

.SH SEE ALSO
.BR ioctl_xfs_fsgetxattr (2),
.BR ioctl_xfs_fsgeometry (2),
.BR ioctl_xfs_fsbulkstat (2),
.BR ioctl_xfs_scrub_metadata (2),
.BR ioctl_xfs_fsinumbers (2),
.BR ioctl_xfs_fscounts (2),
.BR ioctl_xfs_getresblks (2),
.BR ioctl_xfs_getbmap (2),
.BR ioctl_xfs_goingdown (2),
.BR fstatfs (2),
.BR statfs (2),
.BR xfs (5),
.BR xfs_info (8).