path: root/storage/innobase/fsp/fsp0fsp.cc

/*****************************************************************************

Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2017, 2023, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

/******************************************************************//**
@file fsp/fsp0fsp.cc
File space management

Created 11/29/1995 Heikki Tuuri
***********************************************************************/

#include "fsp0fsp.h"
#include "buf0buf.h"
#include "fil0fil.h"
#include "fil0crypt.h"
#include "mtr0log.h"
#include "ut0byte.h"
#include "page0page.h"
#include "srv0srv.h"
#include "srv0start.h"
#include "ibuf0ibuf.h"
#include "btr0btr.h"
#include "btr0sea.h"
#include "dict0boot.h"
#include "log0log.h"
#include "dict0mem.h"
#include "fsp0types.h"
#include "log.h"

/** Returns the first extent descriptor for a segment.
We think of the extent lists of the segment catenated in the order
FSEG_FULL -> FSEG_NOT_FULL -> FSEG_FREE.
@param[in]	inode		segment inode
@param[in]	space		tablespace
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@return the first extent descriptor, or NULL if none */
MY_ATTRIBUTE((nonnull, warn_unused_result))
static
xdes_t*
fseg_get_first_extent(
	fseg_inode_t*		inode,
	const fil_space_t*	space,
	mtr_t*			mtr,
	dberr_t*		err);

ATTRIBUTE_COLD MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Put new extents to the free list if there are free extents above the free
limit. If an extent happens to contain an extent descriptor page, the extent
is put to the FSP_FREE_FRAG list with the page marked as used.
@param[in]	init_space	true if this is a single-table tablespace
and we are only initializing the first extent and the first bitmap pages;
then we will not allocate more extents
@param[in,out]	space		tablespace
@param[in,out]	header		tablespace header
@param[in,out]	mtr		mini-transaction */
static
dberr_t
fsp_fill_free_list(
	bool		init_space,
	fil_space_t*	space,
	buf_block_t*	header,
	mtr_t*		mtr);

/** Allocates a single free page from a segment.
This function implements the intelligent allocation strategy which tries to
minimize file space fragmentation.
@param[in,out]	space			tablespace
@param[in,out]	seg_inode		segment inode
@param[in,out]	iblock			segment inode page
@param[in]	hint			hint of which page would be desirable
@param[in]	direction		if the new page is needed because of
an index page split, and records are inserted there in order, into which
direction they go alphabetically: FSP_DOWN, FSP_UP, FSP_NO_DIR
@param[in,out]	mtr			mini-transaction
@param[in,out]	init_mtr		mtr or another mini-transaction in
which the page should be initialized.
@param[out]	err			error code
@return the allocated page
@retval nullptr	if no page could be allocated */
static
buf_block_t*
fseg_alloc_free_page_low(
	fil_space_t*		space,
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	uint32_t		hint,
	byte			direction,
#ifdef UNIV_DEBUG
	bool			has_done_reservation,
	/*!< whether the space has already been reserved */
#endif /* UNIV_DEBUG */
	mtr_t*			mtr,
	mtr_t*			init_mtr,
	dberr_t*		err)
	MY_ATTRIBUTE((nonnull, warn_unused_result));

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Get the tablespace header block, SX-latched
@param[in]      space           tablespace
@param[in,out]  mtr             mini-transaction
@param[out]     err             error code
@return pointer to the space header, page x-locked
@retval nullptr if the page cannot be retrieved or is corrupted */
static buf_block_t *fsp_get_header(const fil_space_t *space, mtr_t *mtr,
                                   dberr_t *err)
{
  const page_id_t id{space->id, 0};
  buf_block_t *block= mtr->get_already_latched(id, MTR_MEMO_PAGE_SX_FIX);
  if (block)
    *err= DB_SUCCESS;
  else
  {
    block= buf_page_get_gen(id, space->zip_size(), RW_SX_LATCH,
                            nullptr, BUF_GET_POSSIBLY_FREED,
                            mtr, err);
    if (block &&
        space->id != mach_read_from_4(FSP_HEADER_OFFSET + FSP_SPACE_ID +
                                      block->page.frame))
    {
      *err= DB_CORRUPTION;
      block= nullptr;
    }
  }
  return block;
}

/** Set the XDES_FREE_BIT of a page.
@tparam         free    desired value of XDES_FREE_BIT
@param[in]      block   extent descriptor block
@param[in,out]  descr   extent descriptor
@param[in]      offset  page offset within the extent
@param[in,out]  mtr     mini-transaction */
template<bool free>
inline void xdes_set_free(const buf_block_t &block, xdes_t *descr,
                          ulint offset, mtr_t *mtr)
{
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  ut_ad(offset < FSP_EXTENT_SIZE);
  ut_ad(page_align(descr) == block.page.frame);
  compile_time_assert(XDES_BITS_PER_PAGE == 2);
  compile_time_assert(XDES_FREE_BIT == 0);
  compile_time_assert(XDES_CLEAN_BIT == 1);

  ulint index= XDES_BITS_PER_PAGE * offset;
  byte *b= &descr[XDES_BITMAP + (index >> 3)];
  /* xdes_init() should have set all XDES_CLEAN_BIT. */
  ut_ad(!(~*b & 0xaa));
  /* Clear or set XDES_FREE_BIT. */
  byte val= free
    ? static_cast<byte>(*b | 1 << (index & 7))
    : static_cast<byte>(*b & ~(1 << (index & 7)));
  mtr->write<1>(block, b, val);
}

/**
Find a free page.
@param descr   extent descriptor
@param hint    page offset to start searching from (towards larger pages)
@return free page offset
@retval FIL_NULL if no page is free */
inline uint32_t xdes_find_free(const xdes_t *descr, uint32_t hint= 0)
{
  const uint32_t extent_size= FSP_EXTENT_SIZE;
  ut_ad(hint < extent_size);
  for (uint32_t i= hint; i < extent_size; i++)
    if (xdes_is_free(descr, i))
      return i;
  for (uint32_t i= 0; i < hint; i++)
    if (xdes_is_free(descr, i))
      return i;
  return FIL_NULL;
}

/**
Determine the number of used pages in a descriptor.
@param descr  file descriptor
@return number of pages used */
inline uint32_t xdes_get_n_used(const xdes_t *descr)
{
  uint32_t count= 0;

  for (uint32_t i= FSP_EXTENT_SIZE; i--; )
    if (!xdes_is_free(descr, i))
      count++;

  return count;
}

/**
Determine whether a file extent is full.
@param descr  file descriptor
@return whether all pages have been allocated */
inline bool xdes_is_full(const xdes_t *descr)
{
  return FSP_EXTENT_SIZE == xdes_get_n_used(descr);
}

/** Set the state of an extent descriptor.
@param[in]      block   extent descriptor block
@param[in,out]  descr   extent descriptor
@param[in]      state   the state
@param[in,out]  mtr     mini-transaction */
inline void xdes_set_state(const buf_block_t &block, xdes_t *descr,
                           byte state, mtr_t *mtr)
{
  ut_ad(descr && mtr);
  ut_ad(state >= XDES_FREE);
  ut_ad(state <= XDES_FSEG);
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  ut_ad(page_align(descr) == block.page.frame);
  ut_ad(mach_read_from_4(descr + XDES_STATE) <= XDES_FSEG);
  mtr->write<1>(block, XDES_STATE + 3 + descr, state);
}

/**********************************************************************//**
Gets the state of an xdes.
@return state */
UNIV_INLINE
ulint
xdes_get_state(
/*===========*/
	const xdes_t*	descr)	/*!< in: descriptor */
{
	ulint	state;

	ut_ad(descr);
	state = mach_read_from_4(descr + XDES_STATE);
	ut_ad(state - 1 < XDES_FSEG);
	return(state);
}

/**********************************************************************//**
Inits an extent descriptor to the free and clean state. */
inline void xdes_init(const buf_block_t &block, xdes_t *descr, mtr_t *mtr)
{
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  mtr->memset(&block, uint16_t(descr - block.page.frame) + XDES_BITMAP,
              XDES_SIZE - XDES_BITMAP, 0xff);
  xdes_set_state(block, descr, XDES_FREE, mtr);
}

/** Mark a page used in an extent descriptor.
@param[in,out]  seg_inode       segment inode
@param[in,out]  iblock          segment inode page
@param[in]      page            page number
@param[in,out]  descr           extent descriptor
@param[in,out]  xdes            extent descriptor page
@param[in,out]  mtr             mini-transaction
@return error code */
static MY_ATTRIBUTE((nonnull, warn_unused_result))
dberr_t
fseg_mark_page_used(fseg_inode_t *seg_inode, buf_block_t *iblock,
                    ulint page, xdes_t *descr, buf_block_t *xdes, mtr_t *mtr)
{
  ut_ad(fil_page_get_type(iblock->page.frame) == FIL_PAGE_INODE);
  ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
  ut_ad(!memcmp(seg_inode + FSEG_ID, descr + XDES_ID, 4));

  const uint16_t xoffset= uint16_t(descr - xdes->page.frame + XDES_FLST_NODE);
  const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

  if (!xdes_get_n_used(descr))
  {
    /* We move the extent from the free list to the NOT_FULL list */
    if (dberr_t err= flst_remove(iblock, uint16_t(FSEG_FREE + ioffset),
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(iblock, uint16_t(FSEG_NOT_FULL + ioffset),
                                   xdes, xoffset, mtr))
      return err;
  }

  if (UNIV_UNLIKELY(!xdes_is_free(descr, page % FSP_EXTENT_SIZE)))
    return DB_CORRUPTION;

  /* We mark the page as used */
  xdes_set_free<false>(*xdes, descr, page % FSP_EXTENT_SIZE, mtr);

  byte* p_not_full= seg_inode + FSEG_NOT_FULL_N_USED;
  const uint32_t not_full_n_used= mach_read_from_4(p_not_full) + 1;
  mtr->write<4>(*iblock, p_not_full, not_full_n_used);
  if (xdes_is_full(descr))
  {
    /* We move the extent from the NOT_FULL list to the FULL list */
    if (dberr_t err= flst_remove(iblock, uint16_t(FSEG_NOT_FULL + ioffset),
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(iblock, uint16_t(FSEG_FULL + ioffset),
                                   xdes, xoffset, mtr))
      return err;
    mtr->write<4>(*iblock, seg_inode + FSEG_NOT_FULL_N_USED,
                  not_full_n_used - FSP_EXTENT_SIZE);
  }

  return DB_SUCCESS;
}

/** Get pointer to a the extent descriptor of a page.
@param[in,out]	sp_header	tablespace header page, x-latched
@param[in]	space		tablespace
@param[in]	offset		page offset
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@param[out]	desc_block	descriptor block
@param[in]	init_space	whether the tablespace is being initialized
@return pointer to the extent descriptor, NULL if the page does not
exist in the space or if the offset exceeds free limit */
UNIV_INLINE MY_ATTRIBUTE((warn_unused_result))
xdes_t*
xdes_get_descriptor_with_space_hdr(
	buf_block_t*		header,
	const fil_space_t*	space,
	uint32_t		offset,
	mtr_t*			mtr,
	dberr_t*		err = nullptr,
	buf_block_t**		desc_block = nullptr,
	bool			init_space = false)
{
	ut_ad(space->is_owner());
	ut_ad(mtr->memo_contains_flagged(header, MTR_MEMO_PAGE_SX_FIX
					 | MTR_MEMO_PAGE_X_FIX));
	/* Read free limit and space size */
	uint32_t limit = mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT
					  + header->page.frame);
	uint32_t size  = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					  + header->page.frame);
	ut_ad(limit == space->free_limit
	      || (space->free_limit == 0
		  && (init_space
		      || space->purpose == FIL_TYPE_TEMPORARY
		      || (srv_startup_is_before_trx_rollback_phase
			  && (space->id == TRX_SYS_SPACE
			      || srv_is_undo_tablespace(space->id))))));
	ut_ad(size == space->size_in_header);

	if (offset >= size || offset >= limit) {
		return nullptr;
	}

	const unsigned zip_size = space->zip_size();

	uint32_t descr_page_no = xdes_calc_descriptor_page(zip_size, offset);

	buf_block_t* block = header;

	if (descr_page_no) {
		block = buf_page_get_gen(page_id_t(space->id, descr_page_no),
					 zip_size, RW_SX_LATCH, nullptr,
					 BUF_GET_POSSIBLY_FREED, mtr, err);
	}

	if (desc_block) {
		*desc_block = block;
	}

	return block
		? XDES_ARR_OFFSET + XDES_SIZE
		* xdes_calc_descriptor_index(zip_size, offset)
		+ block->page.frame
		: nullptr;
}

MY_ATTRIBUTE((nonnull(1,3), warn_unused_result))
/** Get the extent descriptor of a page.
The page where the extent descriptor resides is x-locked. If the page
offset is equal to the free limit of the space, we will add new
extents from above the free limit to the space free list, if not free
limit == space size. This adding is necessary to make the descriptor
defined, as they are uninitialized above the free limit.
@param[in]	space		tablespace
@param[in]	offset		page offset; if equal to the free limit, we
try to add new extents to the space free list
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@param[out]	xdes		extent descriptor page
@return the extent descriptor */
static xdes_t *xdes_get_descriptor(const fil_space_t *space, uint32_t offset,
                                   mtr_t *mtr, dberr_t *err= nullptr,
                                   buf_block_t **xdes= nullptr)
{
  if (buf_block_t *block=
      buf_page_get_gen(page_id_t(space->id, 0), space->zip_size(), RW_SX_LATCH,
                       nullptr, BUF_GET_POSSIBLY_FREED, mtr, err))
    return xdes_get_descriptor_with_space_hdr(block, space, offset, mtr,
                                              err, xdes);
  return nullptr;
}

MY_ATTRIBUTE((nonnull(3), warn_unused_result))
/** Get a pointer to the extent descriptor. The page where the
extent descriptor resides is x-locked.
@param space    tablespace
@param lst_node file address of the list node contained in the descriptor
@param mtr      mini-transaction
@param err      error code
@param block    extent descriptor block
@return pointer to the extent descriptor */
static inline
xdes_t *xdes_lst_get_descriptor(const fil_space_t &space, fil_addr_t lst_node,
                                mtr_t *mtr, buf_block_t **block= nullptr,
                                dberr_t *err= nullptr)
{
  ut_ad(mtr->memo_contains(space));
  ut_ad(lst_node.boffset < space.physical_size());
  buf_block_t *b;
  if (!block)
    block= &b;
  *block= buf_page_get_gen(page_id_t{space.id, lst_node.page},
                           space.zip_size(), RW_SX_LATCH,
                           nullptr, BUF_GET_POSSIBLY_FREED, mtr, err);
  if (*block)
    return (*block)->page.frame + lst_node.boffset - XDES_FLST_NODE;

  space.set_corrupted();
  return nullptr;
}

/********************************************************************//**
Returns page offset of the first page in extent described by a descriptor.
@return offset of the first page in extent */
static uint32_t xdes_get_offset(const xdes_t *descr)
{
  ut_ad(descr);
  return page_get_page_no(page_align(descr)) +
    uint32_t(((page_offset(descr) - XDES_ARR_OFFSET) / XDES_SIZE) *
             FSP_EXTENT_SIZE);
}

/** Initialize a file page whose prior contents should be ignored.
@param[in,out]	block	buffer pool block */
void fsp_apply_init_file_page(buf_block_t *block)
{
  memset_aligned<UNIV_PAGE_SIZE_MIN>(block->page.frame, 0, srv_page_size);
  const page_id_t id(block->page.id());

  mach_write_to_4(block->page.frame + FIL_PAGE_OFFSET, id.page_no());
  memset_aligned<8>(block->page.frame + FIL_PAGE_PREV, 0xff, 8);
  mach_write_to_4(block->page.frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID,
                  id.space());
  if (page_zip_des_t* page_zip= buf_block_get_page_zip(block))
  {
    memset_aligned<UNIV_ZIP_SIZE_MIN>(page_zip->data, 0,
                                      page_zip_get_size(page_zip));
    static_assert(FIL_PAGE_OFFSET == 4, "compatibility");
    memcpy_aligned<4>(page_zip->data + FIL_PAGE_OFFSET,
                      block->page.frame + FIL_PAGE_OFFSET, 4);
    memset_aligned<8>(page_zip->data + FIL_PAGE_PREV, 0xff, 8);
    static_assert(FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID % 4 == 2,
                  "not perfect alignment");
    memcpy_aligned<2>(page_zip->data + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID,
                      block->page.frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID, 4);
  }
}

#ifdef UNIV_DEBUG
/** Assert that the mini-transaction is compatible with
updating an allocation bitmap page.
@param[in]	mtr	mini-transaction */
void fil_space_t::modify_check(const mtr_t& mtr) const
{
  switch (mtr.get_log_mode()) {
  case MTR_LOG_NONE:
    /* These modes are only allowed within a non-bitmap page
       when there is a higher-level redo log record written. */
    ut_ad(purpose == FIL_TYPE_TABLESPACE || purpose == FIL_TYPE_TEMPORARY);
    break;
  case MTR_LOG_NO_REDO:
    ut_ad(purpose == FIL_TYPE_TEMPORARY || purpose == FIL_TYPE_IMPORT);
    break;
  default:
    /* We may only write redo log for a persistent tablespace. */
    ut_ad(purpose == FIL_TYPE_TABLESPACE);
    ut_ad(mtr.is_named_space(id));
  }
}
#endif

/** Initialize a tablespace header.
@param[in,out]	space	tablespace
@param[in]	size	current size in blocks
@param[in,out]	mtr	mini-transaction
@return error code */
dberr_t fsp_header_init(fil_space_t *space, uint32_t size, mtr_t *mtr)
{
	const page_id_t page_id(space->id, 0);
	const ulint zip_size = space->zip_size();

	buf_block_t *free_block = buf_LRU_get_free_block(false);

	mtr->x_lock_space(space);

	buf_block_t* block = buf_page_create(space, 0, zip_size, mtr,
					     free_block);
	if (UNIV_UNLIKELY(block != free_block)) {
		buf_pool.free_block(free_block);
	}

	space->size_in_header = size;
	space->free_len = 0;
	space->free_limit = 0;

	/* The prior contents of the file page should be ignored */

	fsp_init_file_page(space, block, mtr);

	mtr->write<2>(*block, block->page.frame + FIL_PAGE_TYPE,
		      FIL_PAGE_TYPE_FSP_HDR);

	mtr->write<4,mtr_t::MAYBE_NOP>(*block, FSP_HEADER_OFFSET + FSP_SPACE_ID
				       + block->page.frame, space->id);
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_NOT_USED
				    + block->page.frame));
	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*block, FSP_HEADER_OFFSET + FSP_SIZE
				    + block->page.frame, size);
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT
				    + block->page.frame));
	if (auto f = space->flags & ~FSP_FLAGS_MEM_MASK) {
		mtr->write<4,mtr_t::FORCED>(*block,
					    FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
					    + block->page.frame, f);
	}
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FRAG_N_USED
				    + block->page.frame));

	flst_init(block, FSP_HEADER_OFFSET + FSP_FREE, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_FREE_FRAG, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_FULL_FRAG, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE, mtr);

	mtr->write<8>(*block, FSP_HEADER_OFFSET + FSP_SEG_ID
		      + block->page.frame,
		      1U);

	if (dberr_t err = fsp_fill_free_list(!is_system_tablespace(space->id),
					     space, block, mtr)) {
		return err;
	}

	/* Write encryption metadata to page 0 if tablespace is
	encrypted or encryption is disabled by table option. */
	if (space->crypt_data &&
	    (space->crypt_data->should_encrypt() ||
	     space->crypt_data->not_encrypted())) {
		space->crypt_data->write_page0(block, mtr);
	}

	return DB_SUCCESS;
}

/** Try to extend a single-table tablespace so that a page would fit in the
data file.
@param[in,out]	space	tablespace
@param[in]	page_no	page number
@param[in,out]	header	tablespace header
@param[in,out]	mtr	mini-transaction
@return true if success */
static ATTRIBUTE_COLD __attribute__((warn_unused_result))
bool
fsp_try_extend_data_file_with_pages(
	fil_space_t*	space,
	uint32_t	page_no,
	buf_block_t*	header,
	mtr_t*		mtr)
{
	bool	success;
	ulint	size;

	ut_ad(!is_system_tablespace(space->id));
	ut_d(space->modify_check(*mtr));

	size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
				+ header->page.frame);
	ut_ad(size == space->size_in_header);

	ut_a(page_no >= size);

	success = fil_space_extend(space, page_no + 1);
	/* The size may be less than we wanted if we ran out of disk space. */
	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*header, FSP_HEADER_OFFSET + FSP_SIZE
				    + header->page.frame, space->size);
	space->size_in_header = space->size;

	return(success);
}

/** Calculate the number of physical pages in an extent for this file.
@param[in]	physical_size	page_size of the datafile
@return number of pages in an extent for this file */
inline uint32_t fsp_get_extent_size_in_pages(ulint physical_size)
{
  return uint32_t((FSP_EXTENT_SIZE << srv_page_size_shift) / physical_size);
}


/** Calculate the number of pages to extend a datafile.
We extend single-table tablespaces first one extent at a time,
but 4 at a time for bigger tablespaces. It is not enough to extend always
by one extent, because we need to add at least one extent to FSP_FREE.
A single extent descriptor page will track many extents. And the extent
that uses its extent descriptor page is put onto the FSP_FREE_FRAG list.
Extents that do not use their extent descriptor page are added to FSP_FREE.
The physical page size is used to determine how many extents are tracked
on one extent descriptor page. See xdes_calc_descriptor_page().
@param[in]	physical_size	page size in data file
@param[in]	size		current number of pages in the datafile
@return number of pages to extend the file. */
static uint32_t fsp_get_pages_to_extend_ibd(unsigned physical_size,
					    uint32_t size)
{
	uint32_t extent_size = fsp_get_extent_size_in_pages(physical_size);
	/* The threshold is set at 32MiB except when the physical page
	size is small enough that it must be done sooner. */
	uint32_t threshold = std::min(32 * extent_size, physical_size);

	if (size >= threshold) {
		/* Below in fsp_fill_free_list() we assume
		that we add at most FSP_FREE_ADD extents at
		a time */
		extent_size *= FSP_FREE_ADD;
	}

	return extent_size;
}

/** Try to extend the last data file of a tablespace if it is auto-extending.
@param[in,out]	space	tablespace
@param[in,out]	header	tablespace header
@param[in,out]	mtr	mini-transaction
@return	number of pages added
@retval	0 if the tablespace was not extended */
ATTRIBUTE_COLD __attribute__((nonnull))
static
ulint
fsp_try_extend_data_file(fil_space_t *space, buf_block_t *header, mtr_t *mtr)
{
	const char* OUT_OF_SPACE_MSG =
		"ran out of space. Please add another file or use"
		" 'autoextend' for the last file in setting";

	ut_d(space->modify_check(*mtr));

	if (space->id == TRX_SYS_SPACE
	    && !srv_sys_space.can_auto_extend_last_file()) {

		/* We print the error message only once to avoid
		spamming the error log. Note that we don't need
		to reset the flag to false as dealing with this
		error requires server restart. */
		if (!srv_sys_space.get_tablespace_full_status()) {
			sql_print_error("InnoDB: The InnoDB system tablespace "
                                        "%s" " innodb_data_file_path.",
                                        OUT_OF_SPACE_MSG);
			srv_sys_space.set_tablespace_full_status(true);
		}
		return(0);
	} else if (space->id == SRV_TMP_SPACE_ID
		   && !srv_tmp_space.can_auto_extend_last_file()) {

		/* We print the error message only once to avoid
		spamming the error log. Note that we don't need
		to reset the flag to false as dealing with this
		error requires server restart. */
		if (!srv_tmp_space.get_tablespace_full_status()) {
			sql_print_error("InnoDB: The InnoDB temporary"
                                        " tablespace %s"
                                        " innodb_temp_data_file_path.",
                                        OUT_OF_SPACE_MSG);
			srv_tmp_space.set_tablespace_full_status(true);
		}
		return(0);
	}

	uint32_t size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					 + header->page.frame);
	ut_ad(size == space->size_in_header);
	uint32_t size_increase;

	const unsigned ps = space->physical_size();

	switch (space->id) {
	case TRX_SYS_SPACE:
		size_increase = srv_sys_space.get_increment();
		break;
	case SRV_TMP_SPACE_ID:
		size_increase = srv_tmp_space.get_increment();
		break;
	default:
		uint32_t extent_pages = fsp_get_extent_size_in_pages(ps);
		if (size < extent_pages) {
			/* Let us first extend the file to extent_size */
			if (!fsp_try_extend_data_file_with_pages(
				    space, extent_pages - 1, header, mtr)) {
				return(0);
			}

			size = extent_pages;
		}

		size_increase = fsp_get_pages_to_extend_ibd(ps, size);
	}

	if (size_increase == 0) {
		return(0);
	}

	if (!fil_space_extend(space, size + size_increase)) {
		return(0);
	}

	/* For the system tablespace, we ignore any fragments of a
	full megabyte when storing the size to the space header */

	space->size_in_header = space->id
		? space->size
		: ut_2pow_round(space->size, (1024 * 1024) / ps);

	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*header, FSP_HEADER_OFFSET + FSP_SIZE
				    + header->page.frame,
				    space->size_in_header);

	return(size_increase);
}

/** Reset the page type.
Data files created before MySQL 5.1.48 may contain garbage in FIL_PAGE_TYPE.
In MySQL 3.23.53, only undo log pages and index pages were tagged.
Any other pages were written with uninitialized bytes in FIL_PAGE_TYPE.
@param[in]	block	block with invalid FIL_PAGE_TYPE
@param[in]	type	expected page type
@param[in,out]	mtr	mini-transaction */
ATTRIBUTE_COLD
void fil_block_reset_type(const buf_block_t& block, ulint type, mtr_t* mtr)
{
  ib::info() << "Resetting invalid page " << block.page.id() << " type "
             << fil_page_get_type(block.page.frame) << " to " << type << ".";
  mtr->write<2>(block, block.page.frame + FIL_PAGE_TYPE, type);
}

/** Put new extents to the free list if there are free extents above the free
limit. If an extent happens to contain an extent descriptor page, the extent
is put to the FSP_FREE_FRAG list with the page marked as used.
@param[in]	init_space	true if this is a single-table tablespace
and we are only initializing the first extent and the first bitmap pages;
then we will not allocate more extents
@param[in,out]	space		tablespace
@param[in,out]	header		tablespace header
@param[in,out]	mtr		mini-transaction
@return error code */
static
dberr_t
fsp_fill_free_list(
	bool		init_space,
	fil_space_t*	space,
	buf_block_t*	header,
	mtr_t*		mtr)
{
  ut_d(space->modify_check(*mtr));

  /* Check if we can fill free list from above the free list limit */
  uint32_t size=
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE + header->page.frame);
  uint32_t limit=
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT + header->page.frame);

  ut_ad(size == space->size_in_header);
  ut_ad(limit == space->free_limit);

  const auto zip_size= space->zip_size();

  if (size < limit + FSP_EXTENT_SIZE * FSP_FREE_ADD)
  {
    bool skip_resize= init_space;
    switch (space->id) {
    case TRX_SYS_SPACE:
      skip_resize= !srv_sys_space.can_auto_extend_last_file();
      break;
    case SRV_TMP_SPACE_ID:
      skip_resize= !srv_tmp_space.can_auto_extend_last_file();
      break;
    }

    if (!skip_resize)
    {
      fsp_try_extend_data_file(space, header, mtr);
      size= space->size_in_header;
    }
  }

  uint32_t count= 0;
  for (uint32_t i= limit, extent_size= FSP_EXTENT_SIZE,
         physical_size= space->physical_size();
       (init_space && i < 1) ||
         (i + extent_size <= size && count < FSP_FREE_ADD);
       i += extent_size)
  {
    const bool init_xdes= !ut_2pow_remainder(i, physical_size);
    space->free_limit= i + extent_size;
    mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FREE_LIMIT +
                  header->page.frame, i + extent_size);

    if (init_xdes)
    {
      /* We are going to initialize a new descriptor page
      and a new ibuf bitmap page: the prior contents of the
      pages should be ignored. */

      if (i)
      {
        buf_block_t *f= buf_LRU_get_free_block(false);
        buf_block_t *block= buf_page_create(space, i, zip_size, mtr, f);
        if (UNIV_UNLIKELY(block != f))
          buf_pool.free_block(f);
        fsp_init_file_page(space, block, mtr);
        mtr->write<2>(*block, FIL_PAGE_TYPE + block->page.frame,
                      FIL_PAGE_TYPE_XDES);
      }

      if (space->purpose != FIL_TYPE_TEMPORARY)
      {
        buf_block_t *f= buf_LRU_get_free_block(false);
        buf_block_t *block=
          buf_page_create(space, i + FSP_IBUF_BITMAP_OFFSET, zip_size, mtr, f);
        if (UNIV_UNLIKELY(block != f))
          buf_pool.free_block(f);
        fsp_init_file_page(space, block, mtr);
        mtr->write<2>(*block, FIL_PAGE_TYPE + block->page.frame,
                      FIL_PAGE_IBUF_BITMAP);
      }
    }

    buf_block_t *xdes= nullptr;
    xdes_t *descr;
    {
      dberr_t err= DB_SUCCESS;
      descr= xdes_get_descriptor_with_space_hdr(header, space, i, mtr,
                                                &err, &xdes, init_space);
      if (!descr)
        return err;
    }

    if (xdes != header && !space->full_crc32())
      fil_block_check_type(*xdes, FIL_PAGE_TYPE_XDES, mtr);
    xdes_init(*xdes, descr, mtr);
    const uint16_t xoffset=
      static_cast<uint16_t>(descr - xdes->page.frame + XDES_FLST_NODE);
    if (UNIV_UNLIKELY(init_xdes))
    {
      /* The first page in the extent is a descriptor page and the
      second is an ibuf bitmap page: mark them used */
      xdes_set_free<false>(*xdes, descr, 0, mtr);
      xdes_set_free<false>(*xdes, descr, FSP_IBUF_BITMAP_OFFSET, mtr);
      xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
      if (dberr_t err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
                                     xdes, xoffset, mtr))
        return err;
      byte *n_used= FSP_HEADER_OFFSET + FSP_FRAG_N_USED + header->page.frame;
      mtr->write<4>(*header, n_used, 2U + mach_read_from_4(n_used));
    }
    else
    {
      if (dberr_t err=
          flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE,
                        xdes, xoffset, mtr))
        return err;
      count++;
    }
  }

  space->free_len+= count;
  return DB_SUCCESS;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocates a new free extent.
@param[in,out]	space		tablespace
@param[in]	hint		hint of which extent would be desirable: any
page offset in the extent goes; the hint must not be > FSP_FREE_LIMIT
@param[out]	xdes		extent descriptor page
@param[in,out]	mtr		mini-transaction
@return extent descriptor
@retval nullptr if cannot be allocated */
static xdes_t *fsp_alloc_free_extent(fil_space_t *space, uint32_t hint,
                                     buf_block_t **xdes, mtr_t *mtr,
                                     dberr_t *err)
{
	fil_addr_t	first;
	xdes_t*		descr;
	buf_block_t*	desc_block;

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
corrupted:
		space->set_corrupted();
		return nullptr;
	}

	descr = xdes_get_descriptor_with_space_hdr(
		header, space, hint, mtr, err, &desc_block);
	if (!descr) {
		goto corrupted;
	}

	if (desc_block != header && !space->full_crc32()) {
		fil_block_check_type(*desc_block, FIL_PAGE_TYPE_XDES, mtr);
	}

	if (xdes_get_state(descr) == XDES_FREE) {
		/* Ok, we can take this extent */
	} else {
		/* Take the first extent in the free list */
		first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE
				       + header->page.frame);

		if (first.page == FIL_NULL) {
			*err = fsp_fill_free_list(false, space, header, mtr);
			if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
				goto corrupted;
			}

			first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE
					       + header->page.frame);
			if (first.page == FIL_NULL) {
				return nullptr;	/* No free extents left */
			}
		}

		descr = xdes_lst_get_descriptor(*space, first, mtr,
						&desc_block, err);
		if (!descr) {
			return descr;
		}
	}

	*err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE, desc_block,
			   static_cast<uint16_t>(descr - desc_block->page.frame
						 + XDES_FLST_NODE),
			   mtr);
	if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
		return nullptr;
	}

	space->free_len--;
	*xdes = desc_block;

	return(descr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a single free page.
@param[in,out]	header	tablespace header
@param[in,out]	xdes	extent descriptor page
@param[in,out]	descr	extent descriptor
@param[in]	bit	slot to allocate in the extent
@param[in,out]	mtr	mini-transaction
@return error code */
static dberr_t
fsp_alloc_from_free_frag(buf_block_t *header, buf_block_t *xdes, xdes_t *descr,
			 ulint bit, mtr_t *mtr)
{
  if (UNIV_UNLIKELY(xdes_get_state(descr) != XDES_FREE_FRAG ||
                    !xdes_is_free(descr, bit)))
    return DB_CORRUPTION;
  xdes_set_free<false>(*xdes, descr, bit, mtr);

  /* Update the FRAG_N_USED field */
  byte *n_used_p= FSP_HEADER_OFFSET + FSP_FRAG_N_USED + header->page.frame;
  uint32_t n_used = mach_read_from_4(n_used_p) + 1;

  if (xdes_is_full(descr))
  {
    /* The fragment is full: move it to another list */
    const uint16_t xoffset=
      static_cast<uint16_t>(descr - xdes->page.frame + XDES_FLST_NODE);
    if (dberr_t err= flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_FULL_FRAG,
                                   xdes, xoffset, mtr))
      return err;
    xdes_set_state(*xdes, descr, XDES_FULL_FRAG, mtr);
    n_used-= FSP_EXTENT_SIZE;
  }

  mtr->write<4>(*header, n_used_p, n_used);
  return DB_SUCCESS;
}

/** Gets a buffer block for an allocated page.
@param[in,out]	space		tablespace
@param[in]	offset		page number of the allocated page
@param[in,out]	mtr		mini-transaction
@return block, initialized */
static buf_block_t* fsp_page_create(fil_space_t *space, uint32_t offset,
                                    mtr_t *mtr)
{
  buf_block_t *free_block= buf_LRU_get_free_block(false),
    *block= buf_page_create(space, offset, space->zip_size(), mtr, free_block);
  if (UNIV_UNLIKELY(block != free_block))
    buf_pool.free_block(free_block);
  fsp_init_file_page(space, block, mtr);
  return block;
}

/** Allocates a single free page from a space.
The page is marked as used.
@param[in,out]	space		tablespace
@param[in]	hint		hint of which page would be desirable
@param[in,out]	mtr		mini-transaction
@param[in,out]	init_mtr	mini-transaction in which the page should be
initialized (may be the same as mtr)
@param[out]	err		error code
@return allocated block
@retval nullptr	if no page could be allocated */
static MY_ATTRIBUTE((warn_unused_result, nonnull))
buf_block_t *fsp_alloc_free_page(fil_space_t *space, uint32_t hint,
                                 mtr_t *mtr, mtr_t *init_mtr, dberr_t *err)
{
  ut_d(space->modify_check(*mtr));
  buf_block_t *block= fsp_get_header(space, mtr, err);
  if (!block)
    return block;

  buf_block_t *xdes;
  /* Get the hinted descriptor */
  xdes_t *descr= xdes_get_descriptor_with_space_hdr(block, space, hint, mtr,
                                                    err, &xdes);
  if (descr && xdes_get_state(descr) == XDES_FREE_FRAG)
    /* Ok, we can take this extent */;
  else if (*err != DB_SUCCESS)
  {
  err_exit:
    space->set_corrupted();
    return nullptr;
  }
  else
  {
    /* Else take the first extent in free_frag list */
    fil_addr_t first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE_FRAG +
                                      block->page.frame);
    if (first.page == FIL_NULL)
    {
      /* There are no partially full fragments: allocate a free extent
      and add it to the FREE_FRAG list. NOTE that the allocation may
      have as a side-effect that an extent containing a descriptor
      page is added to the FREE_FRAG list. But we will allocate our
      page from the the free extent anyway. */
      descr= fsp_alloc_free_extent(space, hint, &xdes, mtr, err);
      if (!descr)
        return nullptr;
      *err= flst_add_last(block, FSP_HEADER_OFFSET + FSP_FREE_FRAG, xdes,
                          static_cast<uint16_t>(descr - xdes->page.frame +
                                                XDES_FLST_NODE), mtr);
      if (UNIV_UNLIKELY(*err != DB_SUCCESS))
        return nullptr;
      xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
    }
    else
    {
      descr= xdes_lst_get_descriptor(*space, first, mtr, &xdes, err);
      if (!descr)
        return nullptr;
      /* Reset the hint */
      hint= 0;
    }
  }

  /* Now we have in descr an extent with at least one free page. Look
  for a free page in the extent. */
  uint32_t free= xdes_find_free(descr, hint % FSP_EXTENT_SIZE);
  if (free == FIL_NULL)
  {
  corrupted:
    *err= DB_CORRUPTION;
    goto err_exit;
  }

  uint32_t page_no= xdes_get_offset(descr) + free;
  uint32_t space_size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE +
                                         block->page.frame);
  ut_ad(space_size == space->size_in_header ||
        (space->id == TRX_SYS_SPACE &&
         srv_startup_is_before_trx_rollback_phase));

  if (space_size <= page_no)
  {
    /* It must be that we are extending a single-table tablespace
    whose size is still < 64 pages */
    ut_ad(!is_system_tablespace(space->id));
    if (page_no >= FSP_EXTENT_SIZE)
    {
      sql_print_error("InnoDB: Trying to extend %s"
                      " by single page(s) though the size is " UINT32PF "."
                      " Page no " UINT32PF ".",
                      space->chain.start->name, space_size, page_no);
      goto corrupted;
    }

    if (!fsp_try_extend_data_file_with_pages(space, page_no, block, mtr))
    {
      *err= DB_OUT_OF_FILE_SPACE;
      return nullptr;
    }
  }

  *err= fsp_alloc_from_free_frag(block, xdes, descr, free, mtr);
  if (UNIV_UNLIKELY(*err != DB_SUCCESS))
    goto corrupted;
  return fsp_page_create(space, page_no, init_mtr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Return an extent to the free list of a space.
@param[in,out]  space   tablespace
@param[in]      offset  page number in the extent
@param[in,out]  mtr     mini-transaction
@return error code */
static dberr_t fsp_free_extent(fil_space_t* space, uint32_t offset,
                               mtr_t* mtr)
{
  ut_ad(space->is_owner());
  dberr_t err;
  buf_block_t *block= fsp_get_header(space, mtr, &err);
  if (!block)
    return err;
  buf_block_t *xdes;
  xdes_t *descr= xdes_get_descriptor_with_space_hdr(block, space, offset, mtr,
                                                    &err, &xdes);
  if (!descr)
  {
    ut_ad(err || space->is_stopping());
    return err;
  }

  if (UNIV_UNLIKELY(xdes_get_state(descr) == XDES_FREE))
  {
    space->set_corrupted();
    return DB_CORRUPTION;
  }

  xdes_init(*xdes, descr, mtr);
  space->free_len++;
  return flst_add_last(block, FSP_HEADER_OFFSET + FSP_FREE,
                       xdes, static_cast<uint16_t>(descr - xdes->page.frame +
                                                   XDES_FLST_NODE), mtr);
}

MY_ATTRIBUTE((nonnull))
/** Frees a single page of a space.
The page is marked as free and clean.
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@return error code */
static dberr_t fsp_free_page(fil_space_t *space, uint32_t offset, mtr_t *mtr)
{
	xdes_t*		descr;
	ulint		frag_n_used;

	ut_ad(mtr);
	ut_d(space->modify_check(*mtr));

	/* fprintf(stderr, "Freeing page %lu in space %lu\n", page, space); */

	dberr_t err;
	buf_block_t* header = fsp_get_header(space, mtr, &err);
	if (!header) {
		ut_ad(space->is_stopping());
		return err;
	}
	buf_block_t* xdes;

	descr = xdes_get_descriptor_with_space_hdr(header, space, offset, mtr,
						   &err, &xdes);
	if (!descr) {
		ut_ad(err || space->is_stopping());
		return err;
	}

	const auto state = xdes_get_state(descr);

	switch (state) {
	case XDES_FREE_FRAG:
	case XDES_FULL_FRAG:
		if (!xdes_is_free(descr, offset % FSP_EXTENT_SIZE)) {
			break;
		}
		/* fall through */
	default:
		space->set_corrupted();
		return DB_CORRUPTION;
	}

	frag_n_used = mach_read_from_4(FSP_HEADER_OFFSET + FSP_FRAG_N_USED
				       + header->page.frame);

	const uint16_t xoffset= static_cast<uint16_t>(descr - xdes->page.frame
						      + XDES_FLST_NODE);

	if (state == XDES_FULL_FRAG) {
		/* The fragment was full: move it to another list */
		err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FULL_FRAG,
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
				    xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
		mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FRAG_N_USED
			      + header->page.frame,
			      frag_n_used + FSP_EXTENT_SIZE - 1);
	} else if (UNIV_UNLIKELY(!frag_n_used)) {
		return DB_CORRUPTION;
	} else {
		mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FRAG_N_USED
			      + header->page.frame, frag_n_used - 1);
	}

	mtr->free(*space, static_cast<uint32_t>(offset));
	xdes_set_free<true>(*xdes, descr, offset % FSP_EXTENT_SIZE, mtr);
	ut_ad(err == DB_SUCCESS);

	if (!xdes_get_n_used(descr)) {
		/* The extent has become free: move it to another list */
		err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
				  xdes, xoffset, mtr);
		if (err == DB_SUCCESS) {
			err = fsp_free_extent(space, offset, mtr);
		}
	}

	return err;
}

/** @return Number of segment inodes which fit on a single page */
inline ulint FSP_SEG_INODES_PER_PAGE(ulint physical_size)
{
	return (physical_size - FSEG_ARR_OFFSET - 10) / FSEG_INODE_SIZE;
}

/** Returns the nth inode slot on an inode page.
@param[in]	page		segment inode page
@param[in]	i		inode index on page
@return segment inode */
#define fsp_seg_inode_page_get_nth_inode(page, i)	\
	FSEG_ARR_OFFSET + FSEG_INODE_SIZE * i + page

/** Looks for a used segment inode on a segment inode page.
@param page             segment inode page
@param physical_size    page size
@return segment inode index
@retval ULINT_UNDEFINED if not found */
static
ulint
fsp_seg_inode_page_find_used(const page_t *page, ulint physical_size)
{
  for (ulint i= 0; i < FSP_SEG_INODES_PER_PAGE(physical_size); i++)
  {
    const byte *inode= fsp_seg_inode_page_get_nth_inode(page, i);
    if (mach_read_from_8(FSEG_ID + inode))
    {
      ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
      return i;
    }
  }

  return ULINT_UNDEFINED;
}

/** Looks for an unused segment inode on a segment inode page.
@param[in]	page		segment inode page
@param[in]	i		search forward starting from this index
@param[in]	physical_size	page size
@return segment inode index
@retval ULINT_UNDEFINED if not found */
static
ulint
fsp_seg_inode_page_find_free(const page_t *page, ulint i, ulint physical_size)
{
  for (; i < FSP_SEG_INODES_PER_PAGE(physical_size); i++)
  {
    const byte *inode= fsp_seg_inode_page_get_nth_inode(page, i);
    if (mach_read_from_8(FSEG_ID + inode))
      ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
    else
      /* This is unused */
      return i;
  }
  return ULINT_UNDEFINED;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a file segment inode page.
@param[in,out]  space   tablespace
@param[in,out]  header  tablespace header
@param[in,out]  mtr     mini-transaction
@return error code */
static dberr_t fsp_alloc_seg_inode_page(fil_space_t *space,
                                        buf_block_t *header, mtr_t *mtr)
{
  ut_ad(header->page.id().space() == space->id);
  dberr_t err;
  buf_block_t *block= fsp_alloc_free_page(space, 0, mtr, mtr, &err);

  if (!block)
    return err;

  ut_ad(block->page.lock.not_recursive());

  mtr->write<2>(*block, block->page.frame + FIL_PAGE_TYPE, FIL_PAGE_INODE);

#ifdef UNIV_DEBUG
  const byte *inode= FSEG_ID + FSEG_ARR_OFFSET + block->page.frame;
  for (ulint i= FSP_SEG_INODES_PER_PAGE(space->physical_size()); i--;
       inode += FSEG_INODE_SIZE)
    ut_ad(!mach_read_from_8(inode));
#endif

  return flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                       block, FSEG_INODE_PAGE_NODE, mtr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a file segment inode.
@param[in,out]  space   tablespace
@param[in,out]  header  tablespace header
@param[out]     iblock  segment inode page
@param[in,out]  mtr     mini-transaction
@param[out]     err     error code
@return segment inode
@retval nullptr on failure */
static fseg_inode_t*
fsp_alloc_seg_inode(fil_space_t *space, buf_block_t *header,
                    buf_block_t **iblock, mtr_t *mtr, dberr_t *err)
{
  /* Allocate a new segment inode page if needed. */
  if (!flst_get_len(FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE +
                    header->page.frame))
  {
    *err= fsp_alloc_seg_inode_page(space, header, mtr);
    if (*err != DB_SUCCESS)
      return nullptr;
  }

  const page_id_t page_id
  {
    space->id,
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE + FLST_FIRST +
                     FIL_ADDR_PAGE + header->page.frame)
  };

  buf_block_t *block=
    buf_page_get_gen(page_id, space->zip_size(), RW_SX_LATCH,
                     nullptr, BUF_GET_POSSIBLY_FREED, mtr, err);
  if (!block)
    return nullptr;

  if (!space->full_crc32())
    fil_block_check_type(*block, FIL_PAGE_INODE, mtr);

  const ulint physical_size= space->physical_size();
  ulint n= fsp_seg_inode_page_find_free(block->page.frame, 0, physical_size);

  if (UNIV_UNLIKELY(n >= FSP_SEG_INODES_PER_PAGE(physical_size)))
  {
    *err= DB_CORRUPTION;
    return nullptr;
  }
  fseg_inode_t *inode= fsp_seg_inode_page_get_nth_inode(block->page.frame, n);

  if (ULINT_UNDEFINED == fsp_seg_inode_page_find_free(block->page.frame, n + 1,
                                                      physical_size))
  {
    /* There are no other unused headers left on the page: move it
    to another list */
    *err= flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                      block, FSEG_INODE_PAGE_NODE, mtr);
    if (UNIV_UNLIKELY(*err != DB_SUCCESS))
      return nullptr;
    *err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL,
                        block, FSEG_INODE_PAGE_NODE, mtr);
    if (UNIV_UNLIKELY(*err != DB_SUCCESS))
      return nullptr;
  }

  ut_ad(!mach_read_from_8(inode + FSEG_ID) ||
        !memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
  *iblock= block;
  return inode;
}

MY_ATTRIBUTE((nonnull))
/** Frees a file segment inode.
@param[in,out]	space		tablespace
@param[in,out]	inode		segment inode
@param[in,out]	iblock		segment inode page
@param[in,out]	mtr		mini-transaction */
static void fsp_free_seg_inode(fil_space_t *space, fseg_inode_t *inode,
                               buf_block_t *iblock, mtr_t *mtr)
{
  ut_d(space->modify_check(*mtr));

  dberr_t err;
  buf_block_t *header= fsp_get_header(space, mtr, &err);
  if (!header)
    return;
  if (UNIV_UNLIKELY(memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
  {
    space->set_corrupted();
    return;
  }

  const ulint physical_size= space->physical_size();

  if (ULINT_UNDEFINED == fsp_seg_inode_page_find_free(iblock->page.frame, 0,
                                                      physical_size))
  {
    /* Move the page to another list */
    if (flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL,
                    iblock, FSEG_INODE_PAGE_NODE, mtr) != DB_SUCCESS)
      return;
    if (flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                      iblock, FSEG_INODE_PAGE_NODE, mtr) != DB_SUCCESS)
      return;
  }

  mtr->memset(iblock, page_offset(inode) + FSEG_ID, FSEG_INODE_SIZE, 0);

  if (ULINT_UNDEFINED != fsp_seg_inode_page_find_used(iblock->page.frame,
                                                      physical_size))
    return;

  /* There are no other used headers left on the page: free it */
  if (flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                  iblock, FSEG_INODE_PAGE_NODE, mtr) == DB_SUCCESS)
    fsp_free_page(space, iblock->page.id().page_no(), mtr);
}

MY_ATTRIBUTE((nonnull(1,4,5), warn_unused_result))
/** Returns the file segment inode, page x-latched.
@param[in]	header		segment header
@param[in]	space		space id
@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
@param[in,out]	mtr		mini-transaction
@param[out]	block		inode block
@param[out]	err		error code
@return segment inode, page x-latched
@retrval nullptr if the inode is free or corruption was noticed */
static
fseg_inode_t*
fseg_inode_try_get(
	const fseg_header_t*	header,
	uint32_t		space,
	ulint			zip_size,
	mtr_t*			mtr,
	buf_block_t**		block,
        dberr_t*		err = nullptr)
{
  if (UNIV_UNLIKELY(space != mach_read_from_4(header + FSEG_HDR_SPACE)))
  {
  corrupted:
    if (err)
      *err= DB_CORRUPTION;
    return nullptr;
  }

  *block=
    buf_page_get_gen(page_id_t(space,
                               mach_read_from_4(header + FSEG_HDR_PAGE_NO)),
                     zip_size, RW_SX_LATCH, nullptr, BUF_GET_POSSIBLY_FREED,
                     mtr, err);
  if (!*block)
    return nullptr;

  const uint16_t offset= mach_read_from_2(header + FSEG_HDR_OFFSET);
  if (UNIV_UNLIKELY(offset >= (*block)->physical_size()))
    goto corrupted;

  fseg_inode_t *inode= (*block)->page.frame + offset;
  if (UNIV_UNLIKELY(!mach_read_from_8(inode + FSEG_ID) ||
                    memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
    goto corrupted;

  return inode;
}

/** Get the page number from the nth fragment page slot.
@param inode  file segment findex
@param n      slot index
@return page number
@retval FIL_NULL if not in use */
static uint32_t fseg_get_nth_frag_page_no(const fseg_inode_t *inode, ulint n)
{
	ut_ad(inode);
	ut_ad(n < FSEG_FRAG_ARR_N_SLOTS);
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
	return(mach_read_from_4(inode + FSEG_FRAG_ARR
				+ n * FSEG_FRAG_SLOT_SIZE));
}

/** Set the page number in the nth fragment page slot.
@param[in,out]  inode   segment inode
@param[in,out]  iblock  segment inode page
@param[in]      n       slot index
@param[in]      page_no page number to set
@param[in,out]  mtr     mini-transaction */
inline void fseg_set_nth_frag_page_no(fseg_inode_t *inode, buf_block_t *iblock,
                                      ulint n, ulint page_no, mtr_t *mtr)
{
  ut_ad(n < FSEG_FRAG_ARR_N_SLOTS);
  ut_ad(mtr->memo_contains_flagged(iblock, MTR_MEMO_PAGE_SX_FIX));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));

  mtr->write<4>(*iblock, inode + FSEG_FRAG_ARR + n * FSEG_FRAG_SLOT_SIZE,
                page_no);
}

/**********************************************************************//**
Finds a fragment page slot which is free.
@return slot index; ULINT_UNDEFINED if none found */
static
ulint
fseg_find_free_frag_page_slot(
/*==========================*/
	fseg_inode_t*	inode)	/*!< in: segment inode */
{
	ulint	i;
	ulint	page_no;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		page_no = fseg_get_nth_frag_page_no(inode, i);

		if (page_no == FIL_NULL) {

			return(i);
		}
	}

	return(ULINT_UNDEFINED);
}

/**********************************************************************//**
Finds a fragment page slot which is used and last in the array.
@return slot index; ULINT_UNDEFINED if none found */
static
ulint
fseg_find_last_used_frag_page_slot(
/*===============================*/
	fseg_inode_t*	inode)	/*!< in: segment inode */
{
	ulint	i;
	ulint	page_no;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		page_no = fseg_get_nth_frag_page_no(
			inode, FSEG_FRAG_ARR_N_SLOTS - i - 1);

		if (page_no != FIL_NULL) {

			return(FSEG_FRAG_ARR_N_SLOTS - i - 1);
		}
	}

	return(ULINT_UNDEFINED);
}

/** Calculate reserved fragment page slots.
@param inode  file segment index
@return number of fragment pages */
static ulint fseg_get_n_frag_pages(const fseg_inode_t *inode)
{
	ulint	i;
	ulint	count	= 0;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		if (FIL_NULL != fseg_get_nth_frag_page_no(inode, i)) {
			count++;
		}
	}

	return(count);
}

/** Create a new segment.
@param space                tablespace
@param byte_offset          byte offset of the created segment header
@param mtr                  mini-transaction
@param err                  error code
@param has_done_reservation whether fsp_reserve_free_extents() was invoked
@param block                block where segment header is placed,
                            or NULL to allocate an additional page for that
@return the block where the segment header is placed, x-latched
@retval nullptr if could not create segment */
buf_block_t*
fseg_create(fil_space_t *space, ulint byte_offset, mtr_t *mtr, dberr_t *err,
            bool has_done_reservation, buf_block_t *block)
{
	fseg_inode_t*	inode;
	ib_id_t		seg_id;
	uint32_t	n_reserved;
	bool		reserved_extent = false;

	DBUG_ENTER("fseg_create");

	ut_ad(mtr);
	ut_ad(byte_offset >= FIL_PAGE_DATA);
	ut_ad(byte_offset + FSEG_HEADER_SIZE
	      <= srv_page_size - FIL_PAGE_DATA_END);

	mtr->x_lock_space(space);
	ut_d(space->modify_check(*mtr));

	ut_ad(!block || block->page.id().space() == space->id);

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
		block = nullptr;
		goto funct_exit;
	}

	buf_block_t* iblock;

inode_alloc:
	inode = fsp_alloc_seg_inode(space, header, &iblock, mtr, err);

	if (!inode) {
		block = nullptr;
reserve_extent:
		if (!has_done_reservation && !reserved_extent) {
			*err = fsp_reserve_free_extents(&n_reserved, space, 2,
							FSP_NORMAL, mtr);
			if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
				DBUG_RETURN(nullptr);
			}

			/* Extents reserved successfully. So
			try allocating the page or inode */
			reserved_extent = true;
			if (inode) {
				goto page_alloc;
			}

			goto inode_alloc;
		}

		if (inode) {
			fsp_free_seg_inode(space, inode, iblock, mtr);
		}
		goto funct_exit;
	}

	/* Read the next segment id from space header and increment the
	value in space header */

	seg_id = mach_read_from_8(FSP_HEADER_OFFSET + FSP_SEG_ID
				  + header->page.frame);

	mtr->write<8>(*header,
		      FSP_HEADER_OFFSET + FSP_SEG_ID + header->page.frame,
		      seg_id + 1);
	mtr->write<8>(*iblock, inode + FSEG_ID, seg_id);
	ut_ad(!mach_read_from_4(inode + FSEG_NOT_FULL_N_USED));

	flst_init(*iblock, inode + FSEG_FREE, mtr);
	flst_init(*iblock, inode + FSEG_NOT_FULL, mtr);
	flst_init(*iblock, inode + FSEG_FULL, mtr);

	mtr->memcpy(*iblock, inode + FSEG_MAGIC_N, FSEG_MAGIC_N_BYTES, 4);
	compile_time_assert(FSEG_FRAG_SLOT_SIZE == 4);
	compile_time_assert(FIL_NULL == 0xffffffff);
	mtr->memset(iblock,
		    uint16_t(inode - iblock->page.frame) + FSEG_FRAG_ARR,
		    FSEG_FRAG_SLOT_SIZE * FSEG_FRAG_ARR_N_SLOTS, 0xff);

	if (!block) {
page_alloc:
		block = fseg_alloc_free_page_low(space,
						 inode, iblock, 0, FSP_UP,
#ifdef UNIV_DEBUG
						 has_done_reservation,
#endif /* UNIV_DEBUG */
						 mtr, mtr, err);

		if (!block) {
			ut_ad(!has_done_reservation);
			goto reserve_extent;
		}

		ut_d(const auto x = block->page.lock.x_lock_count());
		ut_ad(x || block->page.lock.not_recursive());
		ut_ad(x <= 2);
		ut_ad(!fil_page_get_type(block->page.frame));
		mtr->write<1>(*block, FIL_PAGE_TYPE + 1 + block->page.frame,
			      FIL_PAGE_TYPE_SYS);
	}

	mtr->write<2>(*block, byte_offset + FSEG_HDR_OFFSET
		      + block->page.frame, page_offset(inode));

	mtr->write<4>(*block, byte_offset + FSEG_HDR_PAGE_NO
		      + block->page.frame, iblock->page.id().page_no());

	mtr->write<4,mtr_t::MAYBE_NOP>(*block, byte_offset + FSEG_HDR_SPACE
				       + block->page.frame, space->id);

funct_exit:
	if (!has_done_reservation && reserved_extent) {
		space->release_free_extents(n_reserved);
	}

	DBUG_RETURN(block);
}

/**********************************************************************//**
Calculates the number of pages reserved by a segment, and how many pages are
currently used.
@return number of reserved pages */
static
ulint
fseg_n_reserved_pages_low(
/*======================*/
	const fseg_inode_t*	inode,	/*!< in: segment inode */
	ulint*		used)	/*!< out: number of pages used (not
				more than reserved) */
{
	*used = mach_read_from_4(inode + FSEG_NOT_FULL_N_USED)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FULL)
		+ fseg_get_n_frag_pages(inode);

	return fseg_get_n_frag_pages(inode)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FREE)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_NOT_FULL)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FULL);
}

/** Calculate the number of pages reserved by a segment,
and how many pages are currently used.
@param[in]      block   buffer block containing the file segment header
@param[in]      header  file segment header
@param[out]     used    number of pages that are used (not more than reserved)
@param[in,out]  mtr     mini-transaction
@return number of reserved pages */
ulint fseg_n_reserved_pages(const buf_block_t &block,
                            const fseg_header_t *header, ulint *used,
                            mtr_t *mtr)
{
  ut_ad(page_align(header) == block.page.frame);
  buf_block_t *iblock;
  if (fseg_inode_t *inode=
      fseg_inode_try_get(header, block.page.id().space(), block.zip_size(),
                         mtr, &iblock))
    return fseg_n_reserved_pages_low(inode, used);
  return *used= 0;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Tries to fill the free list of a segment with consecutive free extents.
This happens if the segment is big enough to allow extents in the free list,
the free list is empty, and the extents can be allocated consecutively from
the hint onward.
@param[in]	inode	segment inode
@param[in,out]	iblock	segment inode page
@param[in]	space	tablespace
@param[in]	hint	hint which extent would be good as the first extent
@param[in,out]	mtr	mini-transaction */
static dberr_t fseg_fill_free_list(const fseg_inode_t *inode,
                                   buf_block_t *iblock, fil_space_t *space,
                                   uint32_t hint, mtr_t *mtr)
{
  ulint	used;

  ut_ad(!((page_offset(inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_d(space->modify_check(*mtr));

  if (fseg_n_reserved_pages_low(inode, &used) <
      FSEG_FREE_LIST_LIMIT * FSP_EXTENT_SIZE)
    /* The segment is too small to allow extents in free list */
    return DB_SUCCESS;

  if (UNIV_UNLIKELY(memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
  {
    space->set_corrupted();
    return DB_CORRUPTION;
  }

  if (flst_get_len(inode + FSEG_FREE) > 0)
    /* Free list is not empty */
    return DB_SUCCESS;

  for (ulint i= 0; i < FSEG_FREE_LIST_MAX_LEN; i++, hint += FSP_EXTENT_SIZE)
  {
    buf_block_t *xdes;
    dberr_t err;
    xdes_t *descr= xdes_get_descriptor(space, hint, mtr, &err, &xdes);
    if (!descr || XDES_FREE != xdes_get_state(descr))
      /* We cannot allocate the desired extent: stop */
      return err;

    descr= fsp_alloc_free_extent(space, hint, &xdes, mtr, &err);
    if (UNIV_UNLIKELY(!descr))
      return err;

    if (dberr_t err=
        flst_add_last(iblock,
                      static_cast<uint16_t>(inode - iblock->page.frame +
                                            FSEG_FREE), xdes,
                      static_cast<uint16_t>(descr - xdes->page.frame +
                                            XDES_FLST_NODE), mtr))
      return err;
    xdes_set_state(*xdes, descr, XDES_FSEG, mtr);
    mtr->memcpy(*xdes, descr + XDES_ID, inode + FSEG_ID, 8);
  }

  return DB_SUCCESS;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocates a free extent for the segment: looks first in the free list of
the segment, then tries to allocate from the space free list.
NOTE that the extent returned still resides in the segment free list, it is
not yet taken off it!
@param[in]	inode		segment inode
@param[in,out]	iblock		segment inode page
@param[out]	xdes		extent descriptor page
@param[in,out]	space		tablespace
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@retval nullptr	if no page could be allocated */
static
xdes_t*
fseg_alloc_free_extent(
	const fseg_inode_t*	inode,
	buf_block_t*		iblock,
	buf_block_t**		xdes,
	fil_space_t*		space,
	mtr_t*			mtr,
	dberr_t*		err)
{
  ut_ad(!((page_offset(inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
  ut_d(space->modify_check(*mtr));

  if (flst_get_len(inode + FSEG_FREE))
  {
    /* Segment free list is not empty, allocate from it */
    return xdes_lst_get_descriptor(*space, flst_get_first(inode + FSEG_FREE),
                                   mtr, xdes, err);
  }

  xdes_t* descr= fsp_alloc_free_extent(space, 0, xdes, mtr, err);
  if (UNIV_UNLIKELY(!descr))
    return descr;
  xdes_set_state(**xdes, descr, XDES_FSEG, mtr);
  mtr->memcpy<mtr_t::MAYBE_NOP>(**xdes, descr + XDES_ID, inode + FSEG_ID, 8);
  *err= flst_add_last(iblock,
                      static_cast<uint16_t>(inode - iblock->page.frame +
                                            FSEG_FREE), *xdes,
                      static_cast<uint16_t>(descr - (*xdes)->page.frame +
                                            XDES_FLST_NODE), mtr);
  if (UNIV_LIKELY(*err != DB_SUCCESS))
    return nullptr;
  /* Try to fill the segment free list */
  *err= fseg_fill_free_list(inode, iblock, space,
                            xdes_get_offset(descr) + FSP_EXTENT_SIZE, mtr);
  if (UNIV_UNLIKELY(*err != DB_SUCCESS))
    return nullptr;

  return descr;
}

/** Allocates a single free page from a segment.
This function implements the intelligent allocation strategy which tries to
minimize file space fragmentation.
@param[in,out]	space			tablespace
@param[in,out]	seg_inode		segment inode
@param[in,out]	iblock			segment inode page
@param[in]	hint			hint of which page would be desirable
@param[in]	direction		if the new page is needed because of
an index page split, and records are inserted there in order, into which
direction they go alphabetically: FSP_DOWN, FSP_UP, FSP_NO_DIR
@param[in,out]	mtr			mini-transaction
@param[in,out]	init_mtr		mtr or another mini-transaction in
which the page should be initialized.
@param[out]	err			error code
@return the allocated page
@retval nullptr	if no page could be allocated */
static
buf_block_t*
fseg_alloc_free_page_low(
	fil_space_t*		space,
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	uint32_t		hint,
	byte			direction,
#ifdef UNIV_DEBUG
	bool			has_done_reservation,
	/*!< whether the space has already been reserved */
#endif /* UNIV_DEBUG */
	mtr_t*			mtr,
	mtr_t*			init_mtr,
	dberr_t*		err)
{
	ib_id_t		seg_id;
	ulint		used;
	ulint		reserved;
	xdes_t*		descr;		/*!< extent of the hinted page */
	uint32_t	ret_page;	/*!< the allocated page offset, FIL_NULL
					if could not be allocated */
	xdes_t*		ret_descr;	/*!< the extent of the allocated page */
	buf_block_t*	xdes;
	ulint		n;

	ut_ad((direction >= FSP_UP) && (direction <= FSP_NO_DIR));
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
	ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
	seg_id = mach_read_from_8(seg_inode + FSEG_ID);

	ut_ad(seg_id);
	ut_d(space->modify_check(*mtr));
	ut_ad(fil_page_get_type(page_align(seg_inode)) == FIL_PAGE_INODE);

	reserved = fseg_n_reserved_pages_low(seg_inode, &used);

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
		return header;
	}

	descr = xdes_get_descriptor_with_space_hdr(header, space, hint, mtr,
						   err, &xdes);
	if (!descr) {
		if (*err != DB_SUCCESS) {
			return nullptr;
		}
		/* Hint outside space or too high above free limit: reset
		hint */
		/* The file space header page is always allocated. */
		hint = 0;
		descr = xdes_get_descriptor(space, hint, mtr, err, &xdes);
		if (!descr) {
			return nullptr;
		}
	}

	/* In the big if-else below we look for ret_page and ret_descr */
	/*-------------------------------------------------------------*/
	if ((xdes_get_state(descr) == XDES_FSEG)
	    && mach_read_from_8(descr + XDES_ID) == seg_id
	    && xdes_is_free(descr, hint % FSP_EXTENT_SIZE)) {
take_hinted_page:
		/* 1. We can take the hinted page
		=================================*/
		ret_descr = descr;
		ret_page = hint;
		/* Skip the check for extending the tablespace. If the
		page hint were not within the size of the tablespace,
		we would have got (descr == NULL) above and reset the hint. */
		goto got_hinted_page;
		/*-----------------------------------------------------------*/
	} else if (xdes_get_state(descr) == XDES_FREE
		   && reserved - used < reserved / FSEG_FILLFACTOR
		   && used >= FSEG_FRAG_LIMIT) {

		/* 2. We allocate the free extent from space and can take
		=========================================================
		the hinted page
		===============*/
		ret_descr = fsp_alloc_free_extent(space, hint, &xdes,
						  mtr, err);

		if (UNIV_UNLIKELY(ret_descr != descr)) {
			if (*err != DB_SUCCESS) {
				*err = DB_CORRUPTION;
			}
			return nullptr;
		}

		xdes_set_state(*xdes, ret_descr, XDES_FSEG, mtr);
		mtr->write<8,mtr_t::MAYBE_NOP>(*xdes, ret_descr + XDES_ID,
					       seg_id);
		*err = flst_add_last(
			iblock,
			static_cast<uint16_t>(seg_inode - iblock->page.frame
					      + FSEG_FREE), xdes,
			static_cast<uint16_t>(ret_descr
					      - xdes->page.frame
					      + XDES_FLST_NODE), mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}

		/* Try to fill the segment free list */
		*err = fseg_fill_free_list(seg_inode, iblock, space,
					   hint + FSP_EXTENT_SIZE, mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}
		goto take_hinted_page;
		/*-----------------------------------------------------------*/
	} else if ((direction != FSP_NO_DIR)
		   && ((reserved - used) < reserved / FSEG_FILLFACTOR)
		   && (used >= FSEG_FRAG_LIMIT)
		   && (ret_descr = fseg_alloc_free_extent(seg_inode, iblock,
							  &xdes, space,
							  mtr, err))) {
		/* 3. We take any free extent (which was already assigned above
		===============================================================
		in the if-condition to ret_descr) and take the lowest or
		========================================================
		highest page in it, depending on the direction
		==============================================*/
		ret_page = xdes_get_offset(ret_descr);

		if (direction == FSP_DOWN) {
			ret_page += FSP_EXTENT_SIZE - 1;
		}
		ut_ad(!has_done_reservation || ret_page != FIL_NULL);
		/*-----------------------------------------------------------*/
	} else if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
		return nullptr;
	} else if ((xdes_get_state(descr) == XDES_FSEG)
		   && mach_read_from_8(descr + XDES_ID) == seg_id
		   && (!xdes_is_full(descr))) {

		/* 4. We can take the page from the same extent as the
		======================================================
		hinted page (and the extent already belongs to the
		==================================================
		segment)
		========*/
		ret_descr = descr;
		ret_page = xdes_find_free(ret_descr, hint % FSP_EXTENT_SIZE);
		if (ret_page == FIL_NULL) {
			ut_ad(!has_done_reservation);
		} else {
			ret_page += xdes_get_offset(ret_descr);
		}
		/*-----------------------------------------------------------*/
	} else if (reserved - used > 0) {
		/* 5. We take any unused page from the segment
		==============================================*/
		fil_addr_t	first;

		if (flst_get_len(seg_inode + FSEG_NOT_FULL) > 0) {
			first = flst_get_first(seg_inode + FSEG_NOT_FULL);
		} else if (flst_get_len(seg_inode + FSEG_FREE) > 0) {
			first = flst_get_first(seg_inode + FSEG_FREE);
		} else {
			ut_ad(!has_done_reservation);
			return(NULL);
		}

		ret_descr = xdes_lst_get_descriptor(*space, first, mtr, &xdes);
		if (!ret_descr) {
			return nullptr;
		}

		ret_page = xdes_find_free(ret_descr);
		if (ret_page == FIL_NULL) {
			ut_ad(!has_done_reservation);
		} else {
			ret_page += xdes_get_offset(ret_descr);
		}
		/*-----------------------------------------------------------*/
	} else if (used < FSEG_FRAG_LIMIT) {
		/* 6. We allocate an individual page from the space
		===================================================*/
		buf_block_t* block = fsp_alloc_free_page(
			space, hint, mtr, init_mtr, err);

		ut_ad(block || !has_done_reservation || *err);

		if (block) {
			/* Put the page in the fragment page array of the
			segment */
			n = fseg_find_free_frag_page_slot(seg_inode);
			if (UNIV_UNLIKELY(n == ULINT_UNDEFINED)) {
				*err = DB_CORRUPTION;
				return nullptr;
			}

			fseg_set_nth_frag_page_no(
				seg_inode, iblock, n,
				block->page.id().page_no(), mtr);
		}

		/* fsp_alloc_free_page() invoked fsp_init_file_page()
		already. */
		return(block);
		/*-----------------------------------------------------------*/
	} else {
		/* 7. We allocate a new extent and take its first page
		======================================================*/
		ret_descr = fseg_alloc_free_extent(seg_inode, iblock, &xdes,
						   space, mtr, err);

		if (!ret_descr) {
			ut_ad(!has_done_reservation || *err);
			return nullptr;
		} else {
			ret_page = xdes_get_offset(ret_descr);
		}
	}

	if (ret_page == FIL_NULL) {
		/* Page could not be allocated */

		ut_ad(!has_done_reservation);
		return(NULL);
	}

	if (space->size <= ret_page && !is_predefined_tablespace(space->id)) {
		/* It must be that we are extending a single-table
		tablespace whose size is still < 64 pages */

		if (ret_page >= FSP_EXTENT_SIZE) {
			sql_print_error("InnoDB: Trying to extend '%s'"
					" by single page(s) though the"
					" space size " UINT32PF "."
					" Page no " UINT32PF ".",
					space->chain.start->name, space->size,
					ret_page);
			ut_ad(!has_done_reservation);
			return(NULL);
		}

		if (!fsp_try_extend_data_file_with_pages(
			    space, ret_page, header, mtr)) {
			/* No disk space left */
			ut_ad(!has_done_reservation);
			return(NULL);
		}
	}

got_hinted_page:
	/* ret_descr == NULL if the block was allocated from free_frag
	(XDES_FREE_FRAG) */
	if (ret_descr != NULL) {
		/* At this point we know the extent and the page offset.
		The extent is still in the appropriate list (FSEG_NOT_FULL
		or FSEG_FREE), and the page is not yet marked as used. */

		ut_d(buf_block_t* xxdes);
		ut_ad(xdes_get_descriptor(space, ret_page, mtr, err, &xxdes)
		      == ret_descr);
		ut_ad(xdes == xxdes);
		ut_ad(xdes_is_free(ret_descr, ret_page % FSP_EXTENT_SIZE));

		*err = fseg_mark_page_used(seg_inode, iblock, ret_page,
                                           ret_descr, xdes, mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}
	}

	return fsp_page_create(space, ret_page, init_mtr);
}

/**********************************************************************//**
Allocates a single free page from a segment. This function implements
the intelligent allocation strategy which tries to minimize file space
fragmentation.
@retval NULL if no page could be allocated */
buf_block_t*
fseg_alloc_free_page_general(
/*=========================*/
	fseg_header_t*	seg_header,/*!< in/out: segment header */
	uint32_t	hint,	/*!< in: hint of which page would be
				desirable */
	byte		direction,/*!< in: if the new page is needed because
				of an index page split, and records are
				inserted there in order, into which
				direction they go alphabetically: FSP_DOWN,
				FSP_UP, FSP_NO_DIR */
	bool		has_done_reservation, /*!< in: true if the caller has
				already done the reservation for the page
				with fsp_reserve_free_extents, then there
				is no need to do the check for this individual
				page */
	mtr_t*		mtr,	/*!< in/out: mini-transaction */
	mtr_t*		init_mtr,/*!< in/out: mtr or another mini-transaction
				in which the page should be initialized. */
	dberr_t*	err)	/*!< out: error code */
{
	fseg_inode_t*	inode;
	fil_space_t*	space;
	buf_block_t*	iblock;
	buf_block_t*	block;
	uint32_t	n_reserved;

	const uint32_t space_id = page_get_space_id(page_align(seg_header));
	space = mtr->x_lock_space(space_id);
	inode = fseg_inode_try_get(seg_header, space_id, space->zip_size(),
				   mtr, &iblock, err);
	if (!inode) {
		return nullptr;
	}
	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	if (!has_done_reservation) {
		*err = fsp_reserve_free_extents(&n_reserved, space, 2,
						FSP_NORMAL, mtr);
		if (*err != DB_SUCCESS) {
			return nullptr;
		}
	}

	block = fseg_alloc_free_page_low(space,
					 inode, iblock, hint, direction,
#ifdef UNIV_DEBUG
					 has_done_reservation,
#endif /* UNIV_DEBUG */
					 mtr, init_mtr, err);

	/* The allocation cannot fail if we have already reserved a
	space for the page. */
	ut_ad(block || !has_done_reservation || *err);

	if (!has_done_reservation) {
		space->release_free_extents(n_reserved);
	}

	return(block);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Check that we have at least n_pages frag pages free in the first extent
of a single-table tablespace, and they are also physically initialized to
the data file. That is we have already extended the data file so that those
pages are inside the data file. If not, this function extends the tablespace
with pages.
@param[in,out]	space	tablespace
@param[in,out]	header	tablespace header, x-latched
@param[in]	size	tablespace size in pages, less than FSP_EXTENT_SIZE
@param[in,out]	mtr	mini-transaction
@param[in]	n_pages	number of pages to reserve
@return error code */
static
dberr_t
fsp_reserve_free_pages(
	fil_space_t*	space,
	buf_block_t*	header,
	ulint		size,
	mtr_t*		mtr,
	uint32_t	n_pages)
{
  ut_ad(space != fil_system.sys_space && space != fil_system.temp_space);
  ut_ad(size < FSP_EXTENT_SIZE);

  dberr_t err= DB_OUT_OF_FILE_SPACE;
  const xdes_t *descr=
    xdes_get_descriptor_with_space_hdr(header, space, 0, mtr, &err);
  if (!descr)
    return err;
  const uint32_t n_used= xdes_get_n_used(descr);
  if (size >= n_used + n_pages)
    return DB_SUCCESS;
  if (n_used > size)
    return DB_CORRUPTION;
  return fsp_try_extend_data_file_with_pages(space, n_used + n_pages - 1,
                                             header, mtr)
    ? DB_SUCCESS
    : DB_OUT_OF_FILE_SPACE;
}

/** Reserves free pages from a tablespace. All mini-transactions which may
use several pages from the tablespace should call this function beforehand
and reserve enough free extents so that they certainly will be able
to do their operation, like a B-tree page split, fully. Reservations
must be released with function fil_space_t::release_free_extents()!

The alloc_type below has the following meaning: FSP_NORMAL means an
operation which will probably result in more space usage, like an
insert in a B-tree; FSP_UNDO means allocation to undo logs: if we are
deleting rows, then this allocation will in the long run result in
less space usage (after a purge); FSP_CLEANING means allocation done
in a physical record delete (like in a purge) or other cleaning operation
which will result in less space usage in the long run. We prefer the latter
two types of allocation: when space is scarce, FSP_NORMAL allocations
will not succeed, but the latter two allocations will succeed, if possible.
The purpose is to avoid dead end where the database is full but the
user cannot free any space because these freeing operations temporarily
reserve some space.

Single-table tablespaces whose size is < FSP_EXTENT_SIZE pages are a special
case. In this function we would liberally reserve several extents for
every page split or merge in a B-tree. But we do not want to waste disk space
if the table only occupies < FSP_EXTENT_SIZE pages. That is why we apply
different rules in that special case, just ensuring that there are n_pages
free pages available.

@param[out]	n_reserved	number of extents actually reserved; if we
				return true and the tablespace size is <
				FSP_EXTENT_SIZE pages, then this can be 0,
				otherwise it is n_ext
@param[in,out]	space		tablespace
@param[in]	n_ext		number of extents to reserve
@param[in]	alloc_type	page reservation type (FSP_BLOB, etc)
@param[in,out]	mtr		the mini transaction
@param[in]	n_pages		for small tablespaces (tablespace size is
				less than FSP_EXTENT_SIZE), number of free
				pages to reserve.
@return error code
@retval DB_SUCCESS if we were able to make the reservation */
dberr_t
fsp_reserve_free_extents(
	uint32_t*	n_reserved,
	fil_space_t*	space,
	uint32_t	n_ext,
	fsp_reserve_t	alloc_type,
	mtr_t*		mtr,
	uint32_t	n_pages)
{
	ulint		reserve;

	ut_ad(mtr);
	*n_reserved = n_ext;

	const uint32_t extent_size = FSP_EXTENT_SIZE;

	mtr->x_lock_space(space);
	const unsigned physical_size = space->physical_size();

	dberr_t err;
	buf_block_t* header = fsp_get_header(space, mtr, &err);
	if (!header) {
		return err;
	}
try_again:
	uint32_t size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					 + header->page.frame);
	ut_ad(size == space->size_in_header);

	if (size < extent_size && n_pages < extent_size / 2) {
		/* Use different rules for small single-table tablespaces */
		*n_reserved = 0;
		return fsp_reserve_free_pages(space, header, size,
					      mtr, n_pages);
	}

	uint32_t n_free_list_ext = flst_get_len(FSP_HEADER_OFFSET + FSP_FREE
						+ header->page.frame);
	ut_ad(space->free_len == n_free_list_ext);

	uint32_t free_limit = mach_read_from_4(FSP_HEADER_OFFSET
					       + FSP_FREE_LIMIT
					       + header->page.frame);
	ut_ad(space->free_limit == free_limit);

	/* Below we play safe when counting free extents above the free limit:
	some of them will contain extent descriptor pages, and therefore
	will not be free extents */

	uint32_t n_free_up;

	if (size >= free_limit) {
		n_free_up = (size - free_limit) / extent_size;
		if (n_free_up) {
			n_free_up--;
			n_free_up -= n_free_up / (physical_size / extent_size);
		}
	} else {
		ut_ad(alloc_type == FSP_BLOB);
		n_free_up = 0;
	}

	uint32_t n_free = n_free_list_ext + n_free_up;

	switch (alloc_type) {
	case FSP_NORMAL:
		/* We reserve 1 extent + 0.5 % of the space size to undo logs
		and 1 extent + 0.5 % to cleaning operations; NOTE: this source
		code is duplicated in the function below! */

		reserve = 2 + ((size / extent_size) * 2) / 200;

		if (n_free <= reserve + n_ext) {

			goto try_to_extend;
		}
		break;
	case FSP_UNDO:
		/* We reserve 0.5 % of the space size to cleaning operations */

		reserve = 1 + ((size / extent_size) * 1) / 200;

		if (n_free <= reserve + n_ext) {

			goto try_to_extend;
		}
		break;
	case FSP_CLEANING:
	case FSP_BLOB:
		reserve = 0;
		break;
	default:
		ut_error;
	}

	if (space->reserve_free_extents(n_free, n_ext)) {
		return DB_SUCCESS;
	}
try_to_extend:
	if (fsp_try_extend_data_file(space, header, mtr)) {
		goto try_again;
	}

	return DB_OUT_OF_FILE_SPACE;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Frees a single page of a segment.
@param[in]	seg_inode	segment inode
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@param[in]	ahi		Drop adaptive hash index
@return error code */
static
dberr_t
fseg_free_page_low(
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	fil_space_t*		space,
	uint32_t		offset,
	mtr_t*			mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool			ahi=false
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
	ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
	ut_ad(iblock->page.frame == page_align(seg_inode));
	ut_d(space->modify_check(*mtr));

#ifdef BTR_CUR_HASH_ADAPT
	if (ahi) {
		btr_search_drop_page_hash_when_freed(
			page_id_t(space->id, offset));
	}
#endif /* BTR_CUR_HASH_ADAPT */

	const uint32_t extent_size = FSP_EXTENT_SIZE;
	ut_ad(ut_is_2pow(extent_size));
	buf_block_t* xdes;
	dberr_t err;
	xdes_t* descr = xdes_get_descriptor(space, offset, mtr, &err, &xdes);

	if (!descr) {
		return err;
	}
	if (UNIV_UNLIKELY(xdes_is_free(descr, offset & (extent_size - 1)))) {
corrupted:
		space->set_corrupted();
		return DB_CORRUPTION;
	}

	if (xdes_get_state(descr) != XDES_FSEG) {
		/* The page is in the fragment pages of the segment */
		for (ulint i = 0;; i++) {
			if (fseg_get_nth_frag_page_no(seg_inode, i)
			    != offset) {
				continue;
			}

			compile_time_assert(FIL_NULL == 0xffffffff);
			mtr->memset(iblock, uint16_t(seg_inode
						     - iblock->page.frame)
				    + FSEG_FRAG_ARR
				    + i * FSEG_FRAG_SLOT_SIZE, 4, 0xff);
			break;
		}

		return fsp_free_page(space, offset, mtr);
	}

	/* If we get here, the page is in some extent of the segment */

	if (UNIV_UNLIKELY(memcmp(descr + XDES_ID, seg_inode + FSEG_ID, 8))) {
		goto corrupted;
	}

	byte* p_not_full = seg_inode + FSEG_NOT_FULL_N_USED;
	uint32_t not_full_n_used = mach_read_from_4(p_not_full);
	const uint16_t xoffset= uint16_t(descr - xdes->page.frame
					 + XDES_FLST_NODE);
	const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

	if (xdes_is_full(descr)) {
		/* The fragment is full: move it to another list */
		err = flst_remove(iblock,
				  static_cast<uint16_t>(FSEG_FULL + ioffset),
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = flst_add_last(iblock, static_cast<uint16_t>(FSEG_NOT_FULL
								  + ioffset),
				    xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		not_full_n_used += extent_size - 1;
	} else {
		if (!not_full_n_used) {
			goto corrupted;
		}
		not_full_n_used--;
	}

	mtr->write<4>(*iblock, p_not_full, not_full_n_used);
	xdes_set_free<true>(*xdes, descr, offset & (extent_size - 1), mtr);

	if (!xdes_get_n_used(descr)) {
		err = flst_remove(iblock, static_cast<uint16_t>(FSEG_NOT_FULL
								+ ioffset),
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = fsp_free_extent(space, offset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
	}

	mtr->free(*space, static_cast<uint32_t>(offset));
	return DB_SUCCESS;
}

/** Free a page in a file segment.
@param[in,out]	seg_header	file segment header
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@param[in]	have_latch	whether space->x_lock() was already called
@return error code */
dberr_t fseg_free_page(fseg_header_t *seg_header, fil_space_t *space,
                       uint32_t offset, mtr_t *mtr, bool have_latch)
{
  buf_block_t *iblock;
  if (have_latch)
    ut_ad(space->is_owner());
  else
    mtr->x_lock_space(space);

  DBUG_PRINT("fseg_free_page",
             ("space_id: " ULINTPF ", page_no: %u", space->id, offset));

  dberr_t err;
  if (fseg_inode_t *seg_inode= fseg_inode_try_get(seg_header,
                                                  space->id, space->zip_size(),
                                                  mtr, &iblock, &err))
  {
    if (!space->full_crc32())
      fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
    return fseg_free_page_low(seg_inode, iblock, space, offset, mtr);
  }

  return err;
}

/** Determine whether a page is allocated.
@param space   tablespace
@param page    page number
@return error code
@retval DB_SUCCESS             if the page is marked as free
@retval DB_SUCCESS_LOCKED_REC  if the page is marked as allocated */
dberr_t fseg_page_is_allocated(fil_space_t *space, unsigned page)
{
  mtr_t mtr;
  uint32_t dpage= xdes_calc_descriptor_page(space->zip_size(), page);
  const unsigned zip_size= space->zip_size();
  dberr_t err= DB_SUCCESS;

  mtr.start();
  if (!space->is_owner())
    mtr.x_lock_space(space);

  if (page >= space->free_limit || page >= space->size_in_header);
  else if (const buf_block_t *b=
           buf_page_get_gen(page_id_t(space->id, dpage), space->zip_size(),
                            RW_S_LATCH, nullptr, BUF_GET_POSSIBLY_FREED,
                            &mtr, &err))
  {
    if (!dpage &&
        (space->free_limit !=
         mach_read_from_4(FSP_FREE_LIMIT + FSP_HEADER_OFFSET +
                          b->page.frame) ||
         space->size_in_header !=
         mach_read_from_4(FSP_SIZE + FSP_HEADER_OFFSET + b->page.frame)))
      err= DB_CORRUPTION;
    else
      err= xdes_is_free(b->page.frame + XDES_ARR_OFFSET + XDES_SIZE
                        * xdes_calc_descriptor_index(zip_size, page),
                        page & (FSP_EXTENT_SIZE - 1))
        ? DB_SUCCESS
        : DB_SUCCESS_LOCKED_REC;
  }

  mtr.commit();
  return err;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Free an extent of a segment to the space free list.
@param[in,out]	seg_inode	segment inode
@param[in,out]	space		tablespace
@param[in]	page		page number in the extent
@param[in,out]	mtr		mini-transaction
@return error code */
static
dberr_t
fseg_free_extent(
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	fil_space_t*		space,
	uint32_t		page,
	mtr_t*			mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool			ahi=false
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	buf_block_t* xdes;
	dberr_t err;
	xdes_t*	descr = xdes_get_descriptor(space, page, mtr, &err, &xdes);

	if (!descr) {
		return err;
	}

	if (UNIV_UNLIKELY(xdes_get_state(descr) != XDES_FSEG
			  || memcmp(descr + XDES_ID, seg_inode + FSEG_ID, 8)
			  || memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N
				    + seg_inode, 4))) {
		return DB_CORRUPTION;
	}
	ut_d(space->modify_check(*mtr));
	const uint32_t first_page_in_extent = page - (page % FSP_EXTENT_SIZE);

	const uint16_t xoffset= uint16_t(descr - xdes->page.frame
					 + XDES_FLST_NODE);
	const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

#ifdef BTR_CUR_HASH_ADAPT
	if (ahi) {
		for (uint32_t i = 0; i < FSP_EXTENT_SIZE; i++) {
			if (!xdes_is_free(descr, i)) {
				/* Drop search system page hash index
				if the page is found in the pool and
				is hashed */
				btr_search_drop_page_hash_when_freed(
					page_id_t(space->id,
						 first_page_in_extent + i));
			}
		}
	}
#endif /* BTR_CUR_HASH_ADAPT */

	uint16_t lst;

	if (xdes_is_full(descr)) {
		lst = static_cast<uint16_t>(FSEG_FULL + ioffset);
remove:
		err = flst_remove(iblock, lst, xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
	} else if (!xdes_get_n_used(descr)) {
		lst = static_cast<uint16_t>(FSEG_FREE + ioffset);
                goto remove;
	} else {
		err = flst_remove(
			iblock, static_cast<uint16_t>(FSEG_NOT_FULL + ioffset),
			xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		uint32_t not_full_n_used = mach_read_from_4(
			FSEG_NOT_FULL_N_USED + seg_inode);
		uint32_t descr_n_used = xdes_get_n_used(descr);
		if (not_full_n_used < descr_n_used) {
			return DB_CORRUPTION;
		}
		mtr->write<4>(*iblock, seg_inode + FSEG_NOT_FULL_N_USED,
			      not_full_n_used - descr_n_used);
	}

	std::vector<uint8_t> going_to_free;
	static_assert(FSP_EXTENT_SIZE_MIN == 256, "compatibility");
	static_assert(FSP_EXTENT_SIZE_MAX == 64, "compatibility");

	for (uint32_t i = 0; i < FSP_EXTENT_SIZE; i++) {
		if (!xdes_is_free(descr, i)) {
			going_to_free.emplace_back(uint8_t(i));
		}
	}

	if (dberr_t err = fsp_free_extent(space, page, mtr)) {
		return err;
	}

	for (uint32_t i : going_to_free) {
		mtr->free(*space, first_page_in_extent + i);
		buf_page_free(space, first_page_in_extent + i, mtr);
	}

	return DB_SUCCESS;
}

/** Frees part of a segment. This function can be used to free
a segment by repeatedly calling this function in different
mini-transactions. Doing the freeing in a single mini-transaction
might result in too big a mini-transaction.
@param	header	segment header; NOTE: if the header resides on first
		page of the frag list of the segment, this pointer
		becomes obsolete after the last freeing step
@param	mtr	mini-transaction
@param	ahi	Drop the adaptive hash index
@return whether the freeing was completed */
bool
fseg_free_step(
	fseg_header_t*	header,
	mtr_t*		mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool		ahi
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	ulint		n;
	fseg_inode_t*	inode;

	const uint32_t space_id = page_get_space_id(page_align(header));
	const uint32_t header_page = page_get_page_no(page_align(header));

	fil_space_t* space = mtr->x_lock_space(space_id);
	xdes_t* descr = xdes_get_descriptor(space, header_page, mtr);

	if (!descr) {
		return true;
	}

	/* Check that the header resides on a page which has not been
	freed yet */

	if (UNIV_UNLIKELY(xdes_is_free(descr,
				       header_page & (FSP_EXTENT_SIZE - 1)))) {
		/* Some corruption was detected: stop the freeing
		in order to prevent a crash. */
		return true;
	}
	buf_block_t* iblock;
	const ulint zip_size = space->zip_size();
	inode = fseg_inode_try_get(header, space_id, zip_size, mtr, &iblock);
	if (!inode || space->is_stopping()) {
		return true;
	}

	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	dberr_t err;
	descr = fseg_get_first_extent(inode, space, mtr, &err);

	if (descr) {
		/* Free the extent held by the segment */
		return fseg_free_extent(inode, iblock, space,
					xdes_get_offset(descr), mtr
#ifdef BTR_CUR_HASH_ADAPT
					, ahi
#endif /* BTR_CUR_HASH_ADAPT */
					) != DB_SUCCESS;
	}

	if (err != DB_SUCCESS || space->is_stopping()) {
		return true;
	}

	/* Free a frag page */
	n = fseg_find_last_used_frag_page_slot(inode);

	if (n == ULINT_UNDEFINED) {
		/* Freeing completed: free the segment inode */
		fsp_free_seg_inode(space, inode, iblock, mtr);
		return true;
	}

	uint32_t page_no = fseg_get_nth_frag_page_no(inode, n);

	if (fseg_free_page_low(inode, iblock, space, page_no, mtr
#ifdef BTR_CUR_HASH_ADAPT
			       , ahi
#endif /* BTR_CUR_HASH_ADAPT */
			       ) != DB_SUCCESS) {
		return true;
	}

	buf_page_free(space, page_no, mtr);

	n = fseg_find_last_used_frag_page_slot(inode);

	if (n == ULINT_UNDEFINED) {
		/* Freeing completed: free the segment inode */
		fsp_free_seg_inode(space, inode, iblock, mtr);

		return true;
	}

	return false;
}

bool
fseg_free_step_not_header(
	fseg_header_t*	header,
	mtr_t*		mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool		ahi
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	fseg_inode_t*	inode;

	const uint32_t space_id = page_get_space_id(page_align(header));
	ut_ad(mtr->is_named_space(space_id));

	fil_space_t*		space = mtr->x_lock_space(space_id);
	buf_block_t*		iblock;

	inode = fseg_inode_try_get(header, space_id, space->zip_size(),
				   mtr, &iblock);
	if (space->is_stopping()) {
		return true;
	}

	if (!inode) {
		ib::warn() << "Double free of "
			   << page_id_t(space_id,
					page_get_page_no(page_align(header)));
		return true;
	}

	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	dberr_t err;
	if (xdes_t* descr = fseg_get_first_extent(inode, space, mtr, &err)) {
		/* Free the extent held by the segment */
		return fseg_free_extent(inode, iblock, space,
					xdes_get_offset(descr),
					mtr
#ifdef BTR_CUR_HASH_ADAPT
					, ahi
#endif /* BTR_CUR_HASH_ADAPT */
					) != DB_SUCCESS;
	} else if (err != DB_SUCCESS) {
		return true;
	}

	/* Free a frag page */

	ulint n = fseg_find_last_used_frag_page_slot(inode);

	if (UNIV_UNLIKELY(n == ULINT_UNDEFINED)) {
		return true;
	}

	uint32_t page_no = fseg_get_nth_frag_page_no(inode, n);

	if (page_no == page_get_page_no(page_align(header))) {
		return true;
	}

	if (fseg_free_page_low(inode, iblock, space, page_no, mtr
#ifdef BTR_CUR_HASH_ADAPT
			       , ahi
#endif /* BTR_CUR_HASH_ADAPT */
			       ) != DB_SUCCESS) {
		return true;
	}
	buf_page_free(space, page_no, mtr);
	return false;
}

/** Returns the first extent descriptor for a segment.
We think of the extent lists of the segment catenated in the order
FSEG_FULL -> FSEG_NOT_FULL -> FSEG_FREE.
@param[in]	inode		segment inode
@param[in]	space		tablespace
@param[in,out]	mtr		mini-transaction
@return the first extent descriptor
@retval nullptr if none, or on corruption */
MY_ATTRIBUTE((nonnull, warn_unused_result))
static
xdes_t*
fseg_get_first_extent(
	fseg_inode_t*		inode,
	const fil_space_t*	space,
	mtr_t*			mtr,
	dberr_t*		err)
{
  if (UNIV_UNLIKELY(space->id != page_get_space_id(page_align(inode)) ||
                    memcmp(inode + FSEG_MAGIC_N, FSEG_MAGIC_N_BYTES, 4)))
  {
  corrupted:
    *err= DB_CORRUPTION;
    return nullptr;
  }

  fil_addr_t first;

  if (flst_get_len(inode + FSEG_FULL))
    first= flst_get_first(inode + FSEG_FULL);
  else if (flst_get_len(inode + FSEG_NOT_FULL))
    first= flst_get_first(inode + FSEG_NOT_FULL);
  else if (flst_get_len(inode + FSEG_FREE))
    first= flst_get_first(inode + FSEG_FREE);
  else
  {
    *err= DB_SUCCESS;
    return nullptr;
  }

  if (first.page == FIL_NULL)
    goto corrupted;

  return xdes_lst_get_descriptor(*space, first, mtr, nullptr, err);
}

#ifdef UNIV_BTR_PRINT
/*******************************************************************//**
Writes info of a segment. */
static void fseg_print_low(const fseg_inode_t *inode)
{
	ulint	space;
	ulint	n_used;
	ulint	n_frag;
	ulint	n_free;
	ulint	n_not_full;
	ulint	n_full;
	ulint	reserved;
	ulint	used;
	ulint	page_no;
	ib_id_t	seg_id;

	space = page_get_space_id(page_align(inode));
	page_no = page_get_page_no(page_align(inode));

	reserved = fseg_n_reserved_pages_low(inode, &used);

	seg_id = mach_read_from_8(inode + FSEG_ID);
	n_used = mach_read_from_4(inode + FSEG_NOT_FULL_N_USED);
	n_frag = fseg_get_n_frag_pages(inode);
	n_free = flst_get_len(inode + FSEG_FREE);
	n_not_full = flst_get_len(inode + FSEG_NOT_FULL);
	n_full = flst_get_len(inode + FSEG_FULL);

	ib::info() << "SEGMENT id " << seg_id
		<< " space " << space << ";"
		<< " page " << page_no << ";"
		<< " res " << reserved << " used " << used << ";"
		<< " full ext " << n_full << ";"
		<< " fragm pages " << n_frag << ";"
		<< " free extents " << n_free << ";"
		<< " not full extents " << n_not_full << ": pages " << n_used;

	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
}

/*******************************************************************//**
Writes info of a segment. */
void
fseg_print(
/*=======*/
	fseg_header_t*	header, /*!< in: segment header */
	mtr_t*		mtr)	/*!< in/out: mini-transaction */
{
  const fil_space_t *space=
    mtr->x_lock_space(page_get_space_id(page_align(header)));
  buf_block_t *block;
  if (fseg_inode_t *inode=
      fseg_inode_try_get(header, space->id, space->zip_size(), mtr, &block))
    fseg_print_low(inode);
}
#endif /* UNIV_BTR_PRINT */

#ifdef UNIV_DEBUG
std::ostream &fseg_header::to_stream(std::ostream &out) const
{
  out << "[fseg_header_t: space="
      << mach_read_from_4(m_header + FSEG_HDR_SPACE)
      << ", page=" << mach_read_from_4(m_header + FSEG_HDR_PAGE_NO)
      << ", offset=" << mach_read_from_2(m_header + FSEG_HDR_OFFSET) << "]";
  return out;
}
#endif /* UNIV_DEBUG */