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.

SEE ALSO

       ioctl(2)