UFFDIO_ZEROPAGE(2const)                                UFFDIO_ZEROPAGE(2const)

NAME
       UFFDIO_ZEROPAGE - zero out a memory range registered with userfaultfd

LIBRARY
       Standard C library (libc, -lc)

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

       int ioctl(int fd, UFFDIO_ZEROPAGE, struct uffdio_zeropage *argp);

       #include <linux/userfaultfd.h>

       struct uffdio_zeropage {
           struct uffdio_range  range;
           __u64                mode;      /* Flags controlling behavior */
           __s64                zeropage;  /* Number of bytes zeroed */
       };

DESCRIPTION
       Zero out a memory range registered with userfaultfd.

       The following value may be bitwise ORed in mode to change the behavior
       of the UFFDIO_ZEROPAGE operation:

       UFFDIO_ZEROPAGE_MODE_DONTWAKE
              Do not wake up the thread that waits for page-fault resolution.

       The zeropage field is used by the kernel to return the number of bytes
       that was actually zeroed, or an error in the same manner as
       UFFDIO_COPY.  If the value returned in the zeropage field doesn't match
       the value that was specified in range.len, the operation fails with the
       error EAGAIN.  The zeropage field is output-only; it is not read by the
       UFFDIO_ZEROPAGE operation.

RETURN VALUE
       This ioctl(2) operation returns 0 on success.  In this case, the entire
       area was zeroed.  On error, -1 is returned and errno is set to indicate
       the error.

ERRORS
       EAGAIN The number of bytes zeroed (i.e., the value returned in the
              zeropage field) does not equal the value that was specified in
              the range.len field.

       EINVAL Either range.start or range.len was not a multiple of the system
              page size; or range.len was zero; or the range specified was
              invalid.

       EINVAL An invalid bit was specified in the mode field.

       ESRCH (since Linux 4.13)
              The faulting process has exited at the time of a UFFDIO_ZEROPAGE
              operation.

STANDARDS
       Linux.

HISTORY
       Linux 4.3.

EXAMPLES
       See userfaultfd(2).

SEE ALSO
       ioctl(2), ioctl_userfaultfd(2), userfaultfd(2)

       linux.git/Documentation/admin-guide/mm/userfaultfd.rst

Linux man-pages 6.19              2026-02-08           UFFDIO_ZEROPAGE(2const)