Section 2 · System calls

ioctl_pagemap_scan.2

Package: man-pages

ioctl_pagemap_scan

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
STANDARDS
HISTORY
SEE ALSO

NAME

ioctl_pagemap_scan − get and/or clear page flags

LIBRARY

Standard C library (libc, −lc)

SYNOPSIS

#include <linux/fs.h> /* Definition of struct pm_scan_arg, **
struct page_region**, and PAGE_IS_* constants */ **
#include <sys/ioctl.h>**

int ioctl(int pagemap_fd**, PAGEMAP_SCAN, struct pm_scan_arg *arg);**

DESCRIPTION

This ioctl(2) is used to get and optionally clear some specific flags from page table entries. The information is returned with PAGE_SIZE granularity.

To start tracking the written state (flag) of a page or range of memory, the UFFD_FEATURE_WP_ASYNC must be enabled by UFFDIO_API ioctl(2) on userfaultfd and memory range must be registered with UFFDIO_REGISTER ioctl(2) in UFFDIO_REGISTER_MODE_WP mode.

Supported page flags

The following page table entry flags are supported: **
PAGE_IS_WPALLOWED**

The page has asynchronous write-protection enabled.

PAGE_IS_WRITTEN

The page has been written to from the time it was write protected.

PAGE_IS_FILE

The page is file backed.

PAGE_IS_PRESENT

The page is present in the memory.

PAGE_IS_SWAPPED

The page is swapped.

PAGE_IS_PFNZERO

The page has zero PFN.

PAGE_IS_HUGE

The page is THP or Hugetlb backed.

Supported operations

The get operation is always performed if the output buffer is specified. The other operations are as following:

PM_SCAN_WP_MATCHING

Write protect the matched pages.

PM_SCAN_CHECK_WPASYNC

Abort the scan when a page is found which doesn’t have the Userfaultfd Asynchronous Write protection enabled.

The struct pm_scan_arg argument

struct pm_scan_arg {
__u64 size;
__u64 flags;
__u64 start;
__u64 end;
__u64 walk_end;
__u64 vec;
__u64 vec_len;
__u64 max_pages
__u64 category_inverted;
__u64 category_mask;
__u64 category_anyof_mask
__u64 return_mask;
};


	size		This field should be set to the size of the structure in bytes, as in sizeof(struct pm_scan_arg).
	flags		The operations to be performed are specified in it.
	start		The starting address of the scan is specified in it.
	end		The ending address of the scan is specified in it.

walk_end

The kernel returns the scan’s ending address in it. The walk_end equal to end means that scan has completed on the entire range.


	vec		The address of page_region array for output.

struct page_region {
__u64 start;
__u64 end;
__u64 categories;
};

vec_len

The length of the page_region struct array.

max_pages

It is the optional limit for the number of output pages required.

category_inverted

PAGE_IS_* categories which values match if 0 instead of 1.

category_mask

Skip pages for which any PAGE_IS_* category doesn’t match.

category_anyof_mask

Skip pages for which no PAGE_IS_* category matches.

return_mask

PAGE_IS_* categories that are to be reported in page_region.

RETURN VALUE

On error, −1 is returned, and errno is set to indicate the error.

ERRORS

Error codes can be one of, but are not limited to, the following:


	EINVAL		Invalid arguments i.e., invalid size of the argument, invalid flags, invalid categories, the start address isn’t aligned with PAGE_SIZE, or vec_len is specified when vec is NULL.
	EFAULT		Invalid arg pointer, invalid vec pointer, or invalid address range specified by start and end.
	ENOMEM		No memory is available.
	EINTR		Fetal signal is pending.

STANDARDS

Linux.

HISTORY

Linux 6.7.