.\" Copyright, The contributors to the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH UFFDIO_WRITEPROTECT 2const 2025-05-06 "Linux man-pages 6.14"
.SH NAME
UFFDIO_WRITEPROTECT
\-
write-protect or write-unprotect a userfaultfd-registered memory range
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/userfaultfd.h>" "  /* Definition of " UFFD* " constants */"
.B #include <sys/ioctl.h>
.P
.BI "int ioctl(int " fd ", UFFDIO_WRITEPROTECT, ...);"
.P
.B #include <linux/userfaultfd.h>
.P
.fi
.EX
.B struct uffdio_writeprotect {
.BR "    struct uffdio_range  range;" "  /* Range to change write permission*/"
.BR "    __u64                mode;" "   /* Mode to change write permission */"
.B };
.EE
.SH DESCRIPTION
Write-protect or write-unprotect a userfaultfd-registered memory range
registered with mode
.BR UFFDIO_REGISTER_MODE_WP .
.P
There are two mode bits that are supported in this structure:
.TP
.B UFFDIO_WRITEPROTECT_MODE_WP
When this mode bit is set,
the ioctl will be a write-protect operation upon the memory range specified by
.IR range .
Otherwise it will be a write-unprotect operation upon the specified range,
which can be used to resolve a userfaultfd write-protect page fault.
.TP
.B UFFDIO_WRITEPROTECT_MODE_DONTWAKE
When this mode bit is set,
do not wake up any thread that waits for
page-fault resolution after the operation.
This can be specified only if
.B UFFDIO_WRITEPROTECT_MODE_WP
is not specified.
.SH RETURN VALUE
On success,
0 is returned.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
The
.I start
or the
.I len
field of the
.I ufdio_range
structure was not a multiple of the system page size; or
.I len
was zero; or the specified range was otherwise invalid.
.TP
.B EAGAIN
The process was interrupted; retry this call.
.TP
.B ENOENT
The range specified in
.I range
is not valid.
For example, the virtual address does not exist,
or not registered with userfaultfd write-protect mode.
.TP
.B EFAULT
Encountered a generic fault during processing.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 5.7.
.SH EXAMPLES
See
.BR userfaultfd (2).
.SH SEE ALSO
.BR ioctl (2),
.BR ioctl_userfaultfd (2),
.BR userfaultfd (2)
.P
.I Documentation/admin\-guide/mm/userfaultfd.rst
in the Linux kernel source tree