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diff --git a/storage/innobase/include/dyn0buf.h b/storage/innobase/include/dyn0buf.h
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+/*****************************************************************************
+
+Copyright (c) 2013, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2018, 2020, 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 include/dyn0buf.h
+The dynamically allocated buffer implementation
+
+Created 2013-03-16 Sunny Bains
+*******************************************************/
+
+#ifndef dyn0buf_h
+#define dyn0buf_h
+
+#include "mem0mem.h"
+#include "dyn0types.h"
+#include "ilist.h"
+
+
+/** Class that manages dynamic buffers. It uses a UT_LIST of
+mtr_buf_t::block_t instances. We don't use STL containers in
+order to avoid the overhead of heap calls. Using a custom memory
+allocator doesn't solve the problem either because we have to get
+the memory from somewhere. We can't use the block_t::m_data as the
+backend for the custom allocator because we would like the data in
+the blocks to be contiguous. */
+class mtr_buf_t {
+public:
+	/** SIZE - sizeof(m_node) + sizeof(m_used) */
+	enum { MAX_DATA_SIZE = DYN_ARRAY_DATA_SIZE
+	       - sizeof(ilist_node<>) + sizeof(uint32_t) };
+
+	class block_t : public ilist_node<> {
+	public:
+
+		block_t()
+		{
+			compile_time_assert(MAX_DATA_SIZE <= (2 << 15));
+			init();
+		}
+
+		/**
+		Gets the number of used bytes in a block.
+		@return	number of bytes used */
+		ulint used() const
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(static_cast<ulint>(m_used & ~DYN_BLOCK_FULL_FLAG));
+		}
+
+		/**
+		Gets pointer to the start of data.
+		@return	pointer to data */
+		byte* start()
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(m_data);
+		}
+
+		/**
+		@return start of data - non const version */
+		byte* begin()
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(m_data);
+		}
+
+		/**
+		@return end of used data - non const version */
+		byte* end()
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(begin() + m_used);
+		}
+
+		/**
+		@return start of data - const version */
+		const byte* begin() const
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(m_data);
+		}
+
+		/**
+		@return end of used data - const version */
+		const byte* end() const
+			MY_ATTRIBUTE((warn_unused_result))
+		{
+			return(begin() + m_used);
+		}
+
+	private:
+		/**
+		@return pointer to start of reserved space */
+		template <typename Type>
+		Type push(uint32_t size)
+		{
+			Type	ptr = reinterpret_cast<Type>(end());
+
+			m_used += size;
+			ut_ad(m_used <= uint32_t(MAX_DATA_SIZE));
+
+			return(ptr);
+		}
+
+		/**
+		Grow the stack. */
+		void close(const byte* ptr)
+		{
+			/* Check that it is within bounds */
+			ut_ad(ptr >= begin());
+			ut_ad(ptr <= begin() + m_buf_end);
+
+			/* We have done the boundary check above */
+			m_used = uint32_t(ptr - begin());
+
+			ut_ad(m_used <= MAX_DATA_SIZE);
+			ut_d(m_buf_end = 0);
+		}
+
+		/**
+		Initialise the block */
+		void init()
+		{
+			m_used = 0;
+			ut_d(m_buf_end = 0);
+			ut_d(m_magic_n = DYN_BLOCK_MAGIC_N);
+		}
+	private:
+#ifdef UNIV_DEBUG
+		/** If opened then this is the buffer end offset, else 0 */
+		ulint		m_buf_end;
+
+		/** Magic number (DYN_BLOCK_MAGIC_N) */
+		ulint		m_magic_n;
+#endif /* UNIV_DEBUG */
+
+		/** Storage */
+		byte		m_data[MAX_DATA_SIZE];
+
+		/** number of data bytes used in this block;
+		DYN_BLOCK_FULL_FLAG is set when the block becomes full */
+		uint32_t	m_used;
+
+		friend class mtr_buf_t;
+	};
+
+	typedef sized_ilist<block_t> list_t;
+
+	/** Default constructor */
+	mtr_buf_t()
+		:
+		m_heap(),
+		m_size()
+	{
+		push_back(&m_first_block);
+	}
+
+	/** Destructor */
+	~mtr_buf_t()
+	{
+		erase();
+	}
+
+	/** Reset the buffer vector */
+	void erase()
+	{
+		if (m_heap != NULL) {
+			mem_heap_free(m_heap);
+			m_heap = NULL;
+
+			/* Initialise the list and add the first block. */
+			m_list.clear();
+			m_list.push_back(m_first_block);
+		} else {
+			m_first_block.init();
+			ut_ad(m_list.size() == 1);
+		}
+
+		m_size = 0;
+	}
+
+	/**
+	Makes room on top and returns a pointer to a buffer in it. After
+	copying the elements, the caller must close the buffer using close().
+	@param size	in bytes of the buffer; MUST be <= MAX_DATA_SIZE!
+	@return	pointer to the buffer */
+	byte* open(ulint size)
+		MY_ATTRIBUTE((warn_unused_result))
+	{
+		ut_ad(size > 0);
+		ut_ad(size <= MAX_DATA_SIZE);
+
+		block_t*	block;
+
+		block = has_space(size) ? back() : add_block();
+
+		ut_ad(block->m_used <= MAX_DATA_SIZE);
+		ut_d(block->m_buf_end = block->m_used + size);
+
+		return(block->end());
+	}
+
+	/**
+	Closes the buffer returned by open.
+	@param ptr	end of used space */
+	void close(const byte* ptr)
+	{
+		ut_ad(!m_list.empty());
+		block_t*	block = back();
+
+		m_size -= block->used();
+
+		block->close(ptr);
+
+		m_size += block->used();
+	}
+
+	/**
+	Makes room on top and returns a pointer to the added element.
+	The caller must copy the element to the pointer returned.
+	@param size	in bytes of the element
+	@return	pointer to the element */
+	template <typename Type>
+	Type push(uint32_t size)
+	{
+		ut_ad(size > 0);
+		ut_ad(size <= MAX_DATA_SIZE);
+
+		block_t*	block;
+
+		block = has_space(size) ? back() : add_block();
+
+		m_size += size;
+
+		/* See ISO C++03 14.2/4 for why "template" is required. */
+
+		return(block->template push<Type>(size));
+	}
+
+	/**
+	Pushes n bytes.
+	@param str	string to write
+	@param len	string length */
+	void push(const byte* ptr, uint32_t len)
+	{
+		while (len > 0) {
+			uint32_t n_copied = std::min(len,
+						     uint32_t(MAX_DATA_SIZE));
+			::memmove(push<byte*>(n_copied), ptr, n_copied);
+
+			ptr += n_copied;
+			len -= n_copied;
+		}
+	}
+
+	/**
+	Returns a pointer to an element in the buffer. const version.
+	@param pos	position of element in bytes from start
+	@return	pointer to element */
+	template <typename Type>
+	const Type at(ulint pos) const
+	{
+		block_t*	block = const_cast<block_t*>(
+			const_cast<mtr_buf_t*>(this)->find(pos));
+
+		return(reinterpret_cast<Type>(block->begin() + pos));
+	}
+
+	/**
+	Returns a pointer to an element in the buffer. non const version.
+	@param pos	position of element in bytes from start
+	@return	pointer to element */
+	template <typename Type>
+	Type at(ulint pos)
+	{
+		block_t*	block = const_cast<block_t*>(find(pos));
+
+		return(reinterpret_cast<Type>(block->begin() + pos));
+	}
+
+	/**
+	Returns the size of the total stored data.
+	@return	data size in bytes */
+	ulint size() const
+		MY_ATTRIBUTE((warn_unused_result))
+	{
+#ifdef UNIV_DEBUG
+		ulint	total_size = 0;
+
+		for (list_t::iterator it = m_list.begin(), end = m_list.end();
+		     it != end; ++it) {
+			total_size += it->used();
+		}
+
+		ut_ad(total_size == m_size);
+#endif /* UNIV_DEBUG */
+		return(m_size);
+	}
+
+	/**
+	Iterate over each block and call the functor.
+	@return	false if iteration was terminated. */
+	template <typename Functor>
+	bool for_each_block(Functor& functor) const
+	{
+		for (list_t::iterator it = m_list.begin(), end = m_list.end();
+		     it != end; ++it) {
+
+			if (!functor(&*it)) {
+				return false;
+			}
+		}
+
+		return(true);
+	}
+
+	/**
+	Iterate over each block and call the functor.
+	@return	false if iteration was terminated. */
+	template <typename Functor>
+	bool for_each_block(const Functor& functor) const
+	{
+		for (typename list_t::iterator it = m_list.begin(),
+					       end = m_list.end();
+		     it != end; ++it) {
+
+			if (!functor(&*it)) {
+				return false;
+			}
+		}
+
+		return(true);
+	}
+
+	/**
+	Iterate over all the blocks in reverse and call the iterator
+	@return	false if iteration was terminated. */
+	template <typename Functor>
+	bool for_each_block_in_reverse(Functor& functor) const
+	{
+		for (list_t::reverse_iterator it = m_list.rbegin(),
+					      end = m_list.rend();
+		     it != end; ++it) {
+
+			if (!functor(&*it)) {
+				return false;
+			}
+		}
+
+		return(true);
+	}
+
+	/**
+	Iterate over all the blocks in reverse and call the iterator
+	@return	false if iteration was terminated. */
+	template <typename Functor>
+	bool for_each_block_in_reverse(const Functor& functor) const
+	{
+		for (list_t::reverse_iterator it = m_list.rbegin(),
+					      end = m_list.rend();
+		     it != end; ++it) {
+
+			if (!functor(&*it)) {
+				return false;
+			}
+		}
+
+		return(true);
+	}
+
+	/**
+	@return the first block */
+	block_t* front()
+		MY_ATTRIBUTE((warn_unused_result))
+	{
+		return &m_list.front();
+	}
+
+	/**
+	@return true if m_first_block block was not filled fully */
+	bool is_small() const
+		MY_ATTRIBUTE((warn_unused_result))
+	{
+		return(m_heap == NULL);
+	}
+
+	/** @return whether the buffer is empty */
+	bool empty() const { return !back()->m_used; }
+
+private:
+	// Disable copying
+	mtr_buf_t(const mtr_buf_t&);
+	mtr_buf_t& operator=(const mtr_buf_t&);
+
+	/**
+	Add the block to the end of the list*/
+	void push_back(block_t* block)
+	{
+		block->init();
+		m_list.push_back(*block);
+	}
+
+	/** @return the last block in the list */
+	block_t* back() const
+	{
+		return &const_cast<block_t&>(m_list.back());
+	}
+
+	/*
+	@return true if request can be fullfilled */
+	bool has_space(ulint size) const
+	{
+		return(back()->m_used + size <= MAX_DATA_SIZE);
+	}
+
+	/*
+	@return true if request can be fullfilled */
+	bool has_space(ulint size)
+	{
+		return(back()->m_used + size <= MAX_DATA_SIZE);
+	}
+
+	/** Find the block that contains the pos.
+	@param pos	absolute offset, it is updated to make it relative
+			to the block
+	@return the block containing the pos. */
+	block_t* find(ulint& pos)
+	{
+		ut_ad(!m_list.empty());
+
+		for (list_t::iterator it = m_list.begin(), end = m_list.end();
+		     it != end; ++it) {
+
+			if (pos < it->used()) {
+				ut_ad(it->used() >= pos);
+
+				return &*it;
+			}
+
+			pos -= it->used();
+		}
+
+		return NULL;
+	}
+
+	/**
+	Allocate and add a new block to m_list */
+	block_t* add_block()
+	{
+		block_t*	block;
+
+		if (m_heap == NULL) {
+			m_heap = mem_heap_create(sizeof(*block));
+		}
+
+		block = reinterpret_cast<block_t*>(
+			mem_heap_alloc(m_heap, sizeof(*block)));
+
+		push_back(block);
+
+		return(block);
+	}
+
+private:
+	/** Heap to use for memory allocation */
+	mem_heap_t*		m_heap;
+
+	/** Allocated blocks */
+	list_t			m_list;
+
+	/** Total size used by all blocks */
+	ulint			m_size;
+
+	/** The default block, should always be the first element. This
+	is for backwards compatibility and to avoid an extra heap allocation
+	for small REDO log records */
+	block_t			m_first_block;
+};
+
+#endif /* dyn0buf_h */