xfsctl(3) — Linux manual page


XFSCTL(3)               Library Functions Manual               XFSCTL(3)

NAME         top

       xfsctl - control XFS filesystems and individual files

C SYNOPSIS         top

       #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         top

       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.

              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_FREESP64 operations are all identical.

              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.

              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.

              See ioctl_xfs_fsgetxattr(2) for more information.

              See ioctl_getbmap(2) for more information.

              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.

              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.

              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.

              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.

              See ioctl_xfs_fsinumbers(2) for more information.

              See ioctl_xfs_fsgeometry(2) for more information.

              See ioctl_xfs_ag_geometry(2) for more information.

              See ioctl_xfs_fsbulkstat(2) for more information.

              See ioctl_xfs_scrub_metadata(2) for more information.

              See ioctl_xfs_fscounts(2) for more information.

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

              See ioctl_xfs_goingdown(2) for more information.

              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         top

       ioctl_xfs_fsgetxattr(2), ioctl_xfs_fsgeometry(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),

COLOPHON         top

       This page is part of the xfsprogs (utilities for XFS filesystems)
       project.  Information about the project can be found at 
       ⟨http://xfs.org/⟩.  If you have a bug report for this manual page,
       send it to linux-xfs@vger.kernel.org.  This page was obtained
       from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git⟩ on
       2020-12-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-12-11.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org


Pages that refer to this page: open(2)handle(3)projects(5)projid(5)xfs(5)xfs_io(8)