xfsctl (3)
NAME
xfsctl - control XFS filesystems and individual filesC SYNOPSIS
#include <xfs/xfs.h>- int xfsctl(const char *path, int fd, int cmd, void *ptr);
int platform_test_xfs_fd(int fd);
DESCRIPTION
File Operations
In order to effect an operation on an individual file, the pathname and descriptor arguments passed to xfsctl identifies the file being operated on. The final argument described below refers to the final argument of xfsctl. All of the data structures and macros mentioned below are defined in the <xfs/xfs_fs.h> header file.
XFS_IOC_ALLOCSP
XFS_IOC_ALLOCSP64
XFS_IOC_FREESP
- XFS_IOC_FREESP64
-
Alter storage space associated with a section of the ordinary
file specified. The section is specified by a variable of type
xfs_flock64_t,
pointed to by the final argument.
The data type
xfs_flock64_t
contains the following members:
l_whence
is 0, 1, or 2 to indicate that the relative offset
l_start
will be measured from the start of the file, the current position, or
the end of the file, respectively (i.e.,
l_start
is the offset from the position specified in
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
l_len
field is currently ignored, and should be set to zero.
XFS_IOC_ALLOCSP, XFS_IOC_ALLOCSP64, XFS_IOC_FREESP and XFS_IOC_FREESP64 operations are all identical.
- 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
bs_dmevmask
and
bs_dmstate
fields of the bulkstat structure.
The data referred to by the final argument is a
struct fsdmidata.
This structure's members are
fsd_dmevmask
and
fsd_dmstate.
The di_dmevmask
field is set to the value in
fsd_dmevmask.
The di_dmstate field is set to the value in
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.
- 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
struct dioattr,
which contains the following members:
d_mem
is the memory alignment requirement of the user's data buffer.
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.
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
read(2)
or
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.
- XFS_IOC_FSGETXATTR
-
Get additional attributes associated with files in XFS file systems.
The final argument points to a variable of type
struct fsxattr,
whose fields include:
fsx_xflags
(extended flag bits),
fsx_extsize
(nominal extent size in file system blocks),
fsx_nextents
(number of data extents in the file).
A
fsx_extsize
value returned indicates that a preferred extent size was previously
set on the file, a
fsx_extsize
of zero indicates that the defaults for that filesystem will be used.
Currently the meaningful bits for the
fsx_xflags
field are:
-
- Bit 0 (0x1) - XFS_XFLAG_REALTIME
- The file is a realtime file.
- Bit 1 (0x2) - XFS_XFLAG_PREALLOC
- The file has preallocated space.
- Bit 3 (0x8) - XFS_XFLAG_IMMUTABLE
- The file is immutable - it cannot be modified, deleted or renamed, no link can be created to this file and no data can be written to the file. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this flag.
- Bit 4 (0x10) - XFS_XFLAG_APPEND
- The file is append-only - it can only be open in append mode for writing. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this flag.
- Bit 5 (0x20) - XFS_XFLAG_SYNC
- All writes to the file are synchronous.
- Bit 6 (0x40) - XFS_XFLAG_NOATIME
- When the file is accessed, its atime record is not modified.
- Bit 7 (0x80) - XFS_XFLAG_NODUMP
- The file should be skipped by backup utilities.
- Bit 8 (0x100) - XFS_XFLAG_RTINHERIT
- Realtime inheritance bit - new files created in the directory will be automatically realtime, and new directories created in the directory will inherit the inheritance bit.
- Bit 9 (0x200) - XFS_XFLAG_PROJINHERIT
- Project inheritance bit - new files and directories created in the directory will inherit the parents project ID. New directories also inherit the project inheritance bit.
- Bit 10 (0x400) - XFS_XFLAG_NOSYMLINKS
- Can only be set on a directory and disallows creation of symbolic links in that directory.
- Bit 11 (0x800) - XFS_XFLAG_EXTSIZE
- Extent size bit - if a basic extent size value is set on the file then the allocator will allocate in multiples of the set size for this file (see XFS_IOC_FSSETXATTR below).
- Bit 12 (0x1000) - XFS_XFLAG_EXTSZINHERIT
- Extent size inheritance bit - new files and directories created in the directory will inherit the parents basic extent size value (see XFS_IOC_FSSETXATTR below). Can only be set on a directory.
- Bit 13 (0x2000) - XFS_XFLAG_NODEFRAG
- No defragment file bit - the file should be skipped during a defragmentation operation. When applied to a directory, new files and directories created will inherit the no-defrag bit.
- Bit 14 (0x4000) - XFS_XFLAG_FILESTREAM
- Filestream allocator bit - allows a directory to reserve an allocation group for exclusive use by files created within that directory. Files being written in other directories will not use the same allocation group and so files within different directories will not interleave extents on disk. The reservation is only active while files are being created and written into the directory.
- Bit 31 (0x80000000) - XFS_XFLAG_HASATTR
- The file has extended attributes associated with it.
-
- XFS_IOC_FSGETXATTRA
-
Identical to
XFS_IOC_FSGETXATTR
except that the
fsx_nextents
field contains the number of attribute extents in the file.
- XFS_IOC_FSSETXATTR
-
Set additional attributes associated with files in XFS file systems.
The final argument points to a variable of type
struct fsxattr,
but only the following fields are used in this call:
fsx_xflags
and
fsx_extsize.
The
fsx_xflags
realtime file bit and the file's extent size may be changed only
when the file is empty, except in the case of a directory where
the extent size can be set at any time (this value is only used
for regular file allocations, so should only be set on a directory
in conjunction with the XFS_XFLAG_EXTSZINHERIT flag).
- XFS_IOC_GETBMAP
-
Get the block map for a segment of a file in an XFS file system.
The final argument points to an arry of variables of type
struct getbmap.
All sizes and offsets in the structure are in units of 512 bytes.
The structure fields include:
bmv_offset
(file offset of segment),
bmv_block
(starting block of segment),
bmv_length
(length of segment),
bmv_count
(number of array entries, including the first), and
bmv_entries
(number of entries filled in).
The first structure in the array is a header, and the remaining
structures in the array contain block map information on return.
The header controls iterative calls to the
XFS_IOC_GETBMAP
command.
The caller fills in the
bmv_offset
and
bmv_length
fields of the header to indicate the area of interest in the file,
and fills in the
bmv_count
field to indicate the length of the array.
If the
bmv_length
value is set to -1 then the length of the interesting area is the rest
of the file.
On return from a call, the header is updated so that the command can be
reused to obtain more information, without re-initializing the structures.
Also on return, the
bmv_entries
field of the header is set to the number of array entries actually filled in.
The non-header structures will be filled in with
bmv_offset,
bmv_block,
and
bmv_length.
If a region of the file has no blocks (is a hole in the file) then the
bmv_block
field is set to -1.
- XFS_IOC_GETBMAPA
-
Identical to
XFS_IOC_GETBMAP
except that information about the attribute fork of the file is returned.
XFS_IOC_RESVSP
- 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
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
xfs_info(8)
reports unwritten=1, then the filesystem was made to flag unwritten extents.
XFS_IOC_UNRESVSP
- 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
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.
- 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
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
xfs_info(8)
reports unwritten=1, then the filesystem was made to flag unwritten extents.
XFS_IOC_PATH_TO_HANDLE XFS_IOC_PATH_TO_FSHANDLE XFS_IOC_FD_TO_HANDLE XFS_IOC_OPEN_BY_HANDLE XFS_IOC_READLINK_BY_HANDLE XFS_IOC_ATTR_LIST_BY_HANDLE XFS_IOC_ATTR_MULTI_BY_HANDLE
- XFS_IOC_FSSETDM_BY_HANDLE
-
These are all interfaces that are used to implement various
libhandle
functions (see
open_by_handle(3)).
They are all subject to change and should not be called directly
by applications.
Filesystem Operations
In order to effect one of the following operations, the pathname and descriptor arguments passed to xfsctl() can be any open file in the XFS filesystem in question.
- XFS_IOC_FSINUMBERS
-
This interface is used to extract a list of valid inode numbers from an
XFS filesystem.
It is intended to be called iteratively, to obtain the entire set of inodes.
The information is passed in and out via a structure of type
xfs_fsop_bulkreq_t
pointed to by the final argument.
lastip
is a pointer to a variable containing the last inode number returned,
initially it should be zero.
icount
is the size of the array of structures specified by
ubuffer.
ubuffer
is the address of an array of structures, of type
xfs_inogrp_t.
This structure has the following elements:
xi_startino
(starting inode number),
xi_alloccount
(count of bits set in xi_allocmask), and
xi_allocmask
(mask of allocated inodes in this group).
The bitmask is 64 bits long, and the least significant bit corresponds to inode
xi_startino.
Each bit is set if the corresponding inode is in use.
ocount
is a pointer to a count of returned values, filled in by the call.
An output
ocount
value of zero means that the inode table has been exhausted.
- XFS_IOC_FSBULKSTAT
-
This interface is used to extract inode information (stat
information) "in bulk" from a filesystem. It is intended to
be called iteratively, to obtain information about the entire
set of inodes in a filesystem.
The information is passed in and out via a structure of type
xfs_fsop_bulkreq_t
pointed to by the final argument.
lastip
is a pointer to a variable containing the last inode number returned,
initially it should be zero.
icount
indicates the size of the array of structures specified by
ubuffer.
ubuffer
is the address of an array of structures of type
xfs_bstat_t.
Many of the elements in the structure are the same as for the stat
structure.
The structure has the following elements:
bs_ino
(inode number),
bs_mode
(type and mode),
bs_nlink
(number of links),
bs_uid
(user id),
bs_gid
(group id),
bs_rdev
(device value),
bs_blksize
(block size of the filesystem),
bs_size
(file size in bytes),
bs_atime
(access time),
bs_mtime
(modify time),
bs_ctime
(inode change time),
bs_blocks
(number of blocks used by the file),
bs_xflags
(extended flags),
bs_extsize
(extent size),
bs_extents
(number of extents),
bs_gen
(generation count),
bs_projid_lo
(project id - low word),
bs_projid_hi
(project id - high word, used when projid32bit feature is enabled),
bs_dmevmask
(DMIG event mask),
bs_dmstate
(DMIG state information), and
bs_aextents
(attribute extent count).
ocount
is a pointer to a count of returned values, filled in by the call.
An output
ocount
value of zero means that the inode table has been exhausted.
- XFS_IOC_FSBULKSTAT_SINGLE
-
This interface is a variant of the
XFS_IOC_FSBULKSTAT
interface, used to obtain information about a single inode.
for an open file in the filesystem of interest.
The same structure is used to pass information in and out of
the kernel, except no output count parameter is used (should
be initialized to zero).
An error is returned if the inode number is invalid.
XFS_IOC_THAW XFS_IOC_FREEZE XFS_IOC_GET_RESBLKS XFS_IOC_SET_RESBLKS XFS_IOC_FSGROWFSDATA XFS_IOC_FSGROWFSLOG XFS_IOC_FSGROWFSRT
- XFS_IOC_FSCOUNTS
-
These interfaces are used to implement various filesystem internal
operations on XFS filesystems.
For
XFS_IOC_FSGEOMETRY
(get filesystem mkfs time information), the output structure is of type
xfs_fsop_geom_t.
For
XFS_FS_COUNTS
(get filesystem dynamic global information), the output structure is of type
xfs_fsop_counts_t.
The remainder of these operations will not be described further
as they are not of general use to applications.
SEE ALSO
fstatfs(2), statfs(2), xfs(5), xfs_info(8).