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NAME

       xfsctl - control XFS filesystems and individual files

C SYNOPSIS

       #include <xfs/xfs.h>

       int xfsctl(const char *path, int fd, int cmd, void *ptr);

       int platform_test_xfs_fd(int fd);
       int platform_test_xfs_path(const char *path);

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 xfsctl() calls to ensure  the  target
       path  and  file  descriptor (both must be supplied) do indeed represent a file from an XFS
       filesystem.  The statfs(2) and 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  platform_test_xfs_fd()  and  platform_test_xfs_path()
       provide a platform-independent mechanism.

   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
       XFS_IOC_FSGETXATTRA
       XFS_IOC_FSSETXATTR
              See ioctl_xfs_fsgetxattr(2) for more information.

       XFS_IOC_GETBMAP
       XFS_IOC_GETBMAPA
       XFS_IOC_GETBMAPX
              See ioctl_getbmap(2) for more information.

       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
              See ioctl_xfs_fsinumbers(2) for more information.

       XFS_IOC_FSGEOMETRY
              See ioctl_xfs_fsop_geometry(2) for more information.

       XFS_IOC_AG_GEOMETRY
              See ioctl_xfs_ag_geometry(2) for more information.

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

       XFS_IOC_SCRUB_METADATA
              See ioctl_xfs_scrub_metadata(2) for more information.

       XFS_IOC_FSCOUNTS
              See ioctl_xfs_fscounts(2) for more information.

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

       XFS_IOC_GOINGDOWN
              See ioctl_xfs_goingdown(2) for more information.

       XFS_IOC_THAW
       XFS_IOC_FREEZE
       XFS_IOC_FSGROWFSDATA
       XFS_IOC_FSGROWFSLOG
       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.

SEE ALSO

       ioctl_xfs_fsgetxattr(2),        ioctl_xfs_fsop_geometry(2),       ioctl_xfs_fsbulkstat(2),
       ioctl_xfs_scrub_metadata(2),        ioctl_xfs_fsinumbers(2),        ioctl_xfs_fscounts(2),
       ioctl_xfs_getresblks(2),    ioctl_xfs_getbmap(2),    ioctl_xfs_goingdown(2),   fstatfs(2),
       statfs(2), xfs(5), xfs_info(8).

                                                                                        XFSCTL(3)