---
name: "UFFDIO_WRITEPROTECT"
section: "2const"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/UFFDIO_WRITEPROTECT"
---

# UFFDIO\_WRITEPROTECT(2const)

write-protect or write-unprotect a userfaultfd-registered memory range

## NAME

UFFDIO\_WRITEPROTECT - write-protect or write-unprotect a userfaultfd-registered memory range

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

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

**int ioctl(int** *fd***, UFFDIO\_WRITEPROTECT, ...);**

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

```
struct uffdio_writeprotect {
    struct uffdio_range  range;  /* Range to change write permission*/
    __u64                mode;   /* Mode to change write permission */
};
```

## DESCRIPTION

Write-protect or write-unprotect a userfaultfd-registered memory range registered with mode **UFFDIO\_REGISTER\_MODE\_WP**.

There are two mode bits that are supported in this structure:

- **UFFDIO\_WRITEPROTECT\_MODE\_WP**

  When this mode bit is set, the ioctl will be a write-protect operation upon the memory range specified by *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.

- **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 **UFFDIO\_WRITEPROTECT\_MODE\_WP** is not specified.

## RETURN VALUE

On success, 0 is returned. On error, -1 is returned and *errno* is set to indicate the error.

## ERRORS

- **EINVAL**

  The *start* or the *len* field of the *ufdio\_range* structure was not a multiple of the system page size; or *len* was zero; or the specified range was otherwise invalid.

- **EAGAIN**

  The process was interrupted; retry this call.

- **ENOENT**

  The range specified in *range* is not valid. For example, the virtual address does not exist, or not registered with userfaultfd write-protect mode.

- **EFAULT**

  Encountered a generic fault during processing.

## STANDARDS

Linux.

## HISTORY

Linux 5.7.

## EXAMPLES

See [**userfaultfd**(2)](/userfaultfd/2.md).

## SEE ALSO

[**ioctl**(2)](/ioctl/2.md), [**ioctl\_userfaultfd**(2)](/ioctl_userfaultfd/2.md), [**userfaultfd**(2)](/userfaultfd/2.md)

*Documentation/admin-guide/mm/userfaultfd.rst* in the Linux kernel source tree