UFFDIO_MOVE(2const) - Linux manual page (original) (raw)

UFFDIOMOVE(2const) UFFDIOMOVE(2const)

NAME top

   UFFDIO_MOVE - atomically move a continuous memory chunk into the
   userfault registered range

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <linux/userfaultfd.h>** /* Definition of **UFFD*** constants */
   **#include <sys/ioctl.h>**

   **int ioctl(int** _fd_**, UFFDIO_MOVE, struct uffdio_move ***_argp_**);**

   **#include <linux/userfaultfd.h>**

   **struct uffdio_move {**
       **__u64  dst;** /* Destination of move */
       **__u64  src;** /* Source of move */
       **__u64  len;** /* Number of bytes to move */
       **__u64  mode;** /* Flags controlling behavior of move */
       **__s64  move;** /* Number of bytes moved, or negated error */
   **};**

DESCRIPTION top

   Atomically move a continuous memory chunk into the userfault
   registered range and optionally wake up the blocked thread.

   The following value may be bitwise ORed in _.mode_ to change the
   behavior of the **UFFDIO_MOVE** operation:

   **UFFDIO_MOVE_MODE_DONTWAKE**
          Do not wake up the thread that waits for page-fault
          resolution

   **UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES**
          Allow holes in the source virtual range that is being
          moved.  When not specified, the holes will result in **ENOENT**
          error.  When specified, the holes will be accounted as
          successfully moved memory.  This is mostly useful to move
          hugepage aligned virtual regions without knowing if there
          are transparent hugepages in the regions or not, but
          preventing the risk of having to split the hugepage during
          the operation.

   The _.move_ field is used by the kernel to return the number of
   bytes that was actually moved, or an error (a negated _[errno](../man3/errno.3.html)_-style
   value).  The _.move_ field is output-only; it is not read by the
   **UFFDIO_MOVE** operation.

RETURN VALUE top

   On success, 0 is returned.  In this case, the entire area was
   moved.

   On error, -1 is returned and _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **EAGAIN** The number of bytes moved (i.e., the value returned in the
          _.move_ field) does not equal the value that was specified in
          the _.len_ field.

   **EINVAL** Either _.dst_ or _.len_ was not a multiple of the system page
          size, or the range specified by _.src_ and _.len_ or _.dst_ and
          _.len_ was invalid.

   **EINVAL** An invalid bit was specified in the _.mode_ field.

   **ENOENT** The source virtual memory range has unmapped holes and
          **UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES** is not set.

   **EEXIST** The destination virtual memory range is fully or partially
          mapped.

   **EBUSY** The pages in the source virtual memory range are either
          pinned or not exclusive to the process.  Once KSM
          deduplicates pages or [fork(2)](../man2/fork.2.html) COW-shares pages during
          [fork(2)](../man2/fork.2.html) with child processes, they are no longer exclusive.
          The kernel might only perform lightweight checks for
          detecting whether the pages are exclusive.  To make the
          operation more likely to succeed, KSM should be disabled,
          [fork(2)](../man2/fork.2.html) should be avoided or **MADV_DONTFORK** should be
          configured for the source virtual memory area before
          [fork(2)](../man2/fork.2.html).

   **ENOMEM** Allocating memory needed for the operation failed.

   **ESRCH** The target process has exited at the time of a **UFFDIO_MOVE**
          operation.

STANDARDS top

   Linux.

HISTORY top

   Linux 6.8.

SEE ALSO top

   [ioctl(2)](../man2/ioctl.2.html), [ioctl_userfaultfd(2)](../man2/ioctl%5Fuserfaultfd.2.html), [userfaultfd(2)](../man2/userfaultfd.2.html)

   _linux.git/Documentation/admin-guide/mm/userfaultfd.rst_

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Linux man-pages 6.15 2025-05-17 UFFDIOMOVE(2const)

Pages that refer to this page:ioctl_userfaultfd(2)