/*-------------------------------------------------------------------------

 *

 * bufmask.c

 *    Routines for buffer masking. Used to mask certain bits

 *    in a page which can be different when the WAL is generated

 *    and when the WAL is applied.

 *

 * Portions Copyright (c) 2016-2025, PostgreSQL Global Development Group

 *

 * Contains common routines required for masking a page.

 *

 * IDENTIFICATION

 *    src/backend/access/common/bufmask.c

 *

 *-------------------------------------------------------------------------

 */

#include "postgres.h"

#include "access/bufmask.h"

/*

 * mask_page_lsn_and_checksum

 *

 * In consistency checks, the LSN of the two pages compared will likely be

 * different because of concurrent operations when the WAL is generated and

 * the state of the page when WAL is applied. Also, mask out checksum as

 * masking anything else on page means checksum is not going to match as well.

 */

void

mask_page_lsn_and_checksum(Page page)

{

  PageHeader  phdr = (PageHeader) page;

  PageXLogRecPtrSet(phdr->pd_lsn, (uint64) MASK_MARKER);

  phdr->pd_checksum = MASK_MARKER;

}

/*

 * mask_page_hint_bits

 *

 * Mask hint bits in PageHeader. We want to ignore differences in hint bits,

 * since they can be set without emitting any WAL.

 */

void

mask_page_hint_bits(Page page)

{

  PageHeader  phdr = (PageHeader) page;

  /* Ignore prune_xid (it's like a hint-bit) */

  phdr->pd_prune_xid = MASK_MARKER;

  /* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */

  PageClearFull(page);

  PageClearHasFreeLinePointers(page);

  /*

   * During replay, if the page LSN has advanced past our XLOG record's LSN,

   * we don't mark the page all-visible. See heap_xlog_visible() for

   * details.

   */

  PageClearAllVisible(page);

}

/*

 * mask_unused_space

 *

 * Mask the unused space of a page between pd_lower and pd_upper.

 */

void

mask_unused_space(Page page)

{

  int     pd_lower = ((PageHeader) page)->pd_lower;

  int     pd_upper = ((PageHeader) page)->pd_upper;

  int     pd_special = ((PageHeader) page)->pd_special;

  /* Sanity check */

  if (pd_lower > pd_upper || pd_special < pd_upper ||

    pd_lower < SizeOfPageHeaderData || pd_special > BLCKSZ)

  {

    elog(ERROR, "invalid page pd_lower %u pd_upper %u pd_special %u",

       pd_lower, pd_upper, pd_special);

  }

  memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);

}

/*

 * mask_lp_flags

 *

 * In some index AMs, line pointer flags can be modified on the primary

 * without emitting any WAL record.

 */

void

mask_lp_flags(Page page)

{

  OffsetNumber offnum,

        maxoff;

  maxoff = PageGetMaxOffsetNumber(page);

  for (offnum = FirstOffsetNumber;

     offnum <= maxoff;

     offnum = OffsetNumberNext(offnum))

  {

    ItemId    itemId = PageGetItemId(page, offnum);

    if (ItemIdIsUsed(itemId))

      itemId->lp_flags = LP_UNUSED;

  }

}

/*

 * mask_page_content

 *

 * In some index AMs, the contents of deleted pages need to be almost

 * completely ignored.

 */

void

mask_page_content(Page page)

{

  /* Mask Page Content */

  memset(page + SizeOfPageHeaderData, MASK_MARKER,

       BLCKSZ - SizeOfPageHeaderData);

  /* Mask pd_lower and pd_upper */

  memset(&((PageHeader) page)->pd_lower, MASK_MARKER,

       sizeof(uint16));

  memset(&((PageHeader) page)->pd_upper, MASK_MARKER,

       sizeof(uint16));

}