Split the code to subroutines.

btr_copy_blob_prefix(): New function: copy the prefix of the externally
stored part of an uncompressed BLOB.

btr_copy_zblob_prefix(): New function: copy the prefix of the externally
stored part of a compressed BLOB.

btr_blob_get_part_len(), btr_blob_get_next_page_no(): Add const qualifier
to the parameter.

that also exists in uncompressed form in the buffer pool, pass the
compressed frame to fil_io() instead of the uncompressed one when
not using the doublewrite buffer.

page checksum of compressed-only blocks.  Pass the compressed page frame
to fil_io() when needed.

page_zip_calc_checksum(): Skip also FIL_PAGE_LSN and FIL_PAGE_FILE_FLUSH_LSN.

buf_flush_init_for_writing(): Expect page to be non-NULL.

and to be flushed to disk.

buf_LRU_free_block(): Enable the freeing of uncompressed pages of
compressed tablespaces.

trx_doublewrite->buf_block_arr[]: Change the type from buf_block_t*
to buf_page_t*.

buf_flush_ready_for_flush(): Add debug assertion.

buf_flush_buffered_writes(), buf_flush_try_page(): Support blocks of type
BUF_BLOCK_ZIP_DIRTY.

buf_flush_post_to_doublewrite_buf(), buf_flush_write_block_low():
Change the type of the parameter from buf_block_t* to buf_page_t*.

buf_flush_init_for_writing(): Allow page to be NULL if page_zip_ is non-NULL.

compressed page) is not protected by block_mutex.  Before releasing
buf_pool->mutex, we can simply assign b->io_fix.  After reacquiring
buf_pool->mutex, we also have to acquire buf_pool->zip_mutex.

of a block, do not release buf_pool->mutex between the time the old control
block is removed from buf_pool->page_hash and the new control block is
added to it.  Prevent operations on the compressed-only block while calling
btr_search_drop_page_hash_index() or page_zip_calc_checksum().

buf_LRU_invalidate_tablespace(): Revert the change done in r1223.
buf_pool->zip_mutex will have been released by
buf_LRU_block_remove_hashed_page() when it returns BUF_BLOCK_ZIP_FREE.

acquired by the caller.

buf_LRU_invalidate_tablespace(): Do not leak buf_pool->zip_mutex when
rescanning the LRU list.

of a dirty block, relocate the control blocks on buf_pool->flush_list
instead of calling buf_flush_insert_into_flush_list().

invoking buf_buddy_alloc().  An IO-fixed block must also be x-latched
when block->mutex and buf_pool->mutex are released.

buf_page_create(): Protect the block during buf_buddy_alloc() by
IO-fixing and X-latching it.

should have been added in r1218.

buf_zip_decompress().  This will prevent btr_cur_search_to_nth_level()
from accessing a half-decompressed leaf page.  Internal B-tree nodes
(non-leaf pages) in B-tree searches are only protected by the tree
latch (index->lock) and by buffer-fixing.

page frame to save memory.

compressed page, copy the contents from the uncompressed page if necessary.

and update the comments.

buf_pool->page_hash and buf_pool->LRU before releasing buf_pool->mutex.

buf_page_init_for_read(), buf_page_create(): Allocate the compressed
page after the block has been added to the buffer pool.  Document the
reason for this.

when calling btr_search_drop_page_hash_index() and uninitialized after that.

buf_page_init(): Declare block->frame valid only in the system tablespace.

trx_sysf_create(): Declare the rest of the page valid, although it is
uninitialized.

buf_buddy_relocate(): Document that src may have been split and some of
it may be in buf_pool->zip_free[j] for some j<i, thus mach_read_from_4()
may be reading from free memory.  Check buffer pages only for addressability,
not for being completely initialized.  Ensure that block descriptors are
completely initialized.

buf_buddy_remove_from_free(): Check prev->state and next->state in
UNIV_DEBUG && UNIV_DEBUG_VALGRIND builds.

buf_buddy_free_low(): Flag the entire block valid prior to invoking
buf_buddy_remove_from_free() in order to avoid a Valgrind warning about
the debug assertion on bpage->state.  Remove the Valgrind check for
buddy being completely allocated.  If it has been split to smaller blocks,
some of those blocks may be free.

We cannot clear the page with memset(), because the page number and
tablespace id have already been stamped on it.

buf_buddy_add_to_free() and buf_buddy_remove_from_free().
Remove some bogus Valgrind warnings.  Improve Valgrind instrumentation.

UNIV_MEM_FREE(): Declare a memory area free.
UNIV_MEM_ALLOC(): Declare a memory area allocated (but uninitialized).
UNIV_MEM_DESC(): Associate a memory area with a control block.
UNIV_MEM_UNDESC(): Unassociate a control block.

trx_sys_create_doublewrite_buf(): Clear the buffer with memset().

buf_page_init(): Add a bogus UNIV_MEM_VALID(block->frame) to silence
valid warnings about InnoDB data pages containing uninitialized data.

buf_LRU_get_free_only(): Add UNIV_MEM_ALLOC(block->frame).

buf_LRU_get_free_block(): Add UNIV_MEM_DESC(block->page.zip.data, block).

buf_LRU_free_block(): Add UNIV_MEM_DESC(b->zip.data, b) when allocating
a compressed-only control block for a compressed page.

buf_LRU_block_free_non_file_page(): Replace UNIV_MEM_INVALID() with
UNIV_MEM_FREE().

buf_LRU_block_remove_hashed_page(): Add UNIV_MEM_UNDESC(bpage) when
deallocating a compressed-only control block.  Add
UNIV_MEM_INVALID(block->frame).  (The frame should be flagged free
by buf_LRU_block_free_non_file_page() moments later.)

buf0buddy.c: Disable some extra checks in Valgrind-instrumented builds.
Add UNIV_MEM_VALID(), UNIV_MEM_INVALID(), UNIV_MEM_FREE(), UNIV_MEM_ALLOC()
as necessary.

buf_buddy_block_free(), buf_buddy_free_low(): Flag the freed bytes
uninitialized.

buf_page_init_for_read(), buf_buddy_relocate(): Do not refer to bpage
after invoking buf_relocate().

buf_buddy_relocate(): Flag src uninitialized.

buf_block_t* to buf_page_t*.  Handle compressed-only blocks.

buf_pool->page_hash corruption.

during the buf_zip_decompress() call.  Otherwise, the block may end
up being freed by another thread.  This bug was caught by the
page_zip_validate() check in buf_LRU_block_remove_hashed_page().

buf_page_init_for_read(): Protect the buf_zip_decompress() call with
an X-lock on the block.

page_zip_validate(): Move the page_is_comp() assertion after the
page header comparison.

objects in the free area.

compressed-only page, restart the scan of the LRU list, because
prev_bpage may have been relocated.

buf_LRU_block_remove_hashed_page(): Note that other compressed pages
or compressed-only blocks may be relocated when freeing a compressed
page or a compressed-only block descriptor.

dirty uncompressed blocks.  Move the page_zip_validate() call to
a more appropriate place, buf_LRU_block_remove_hashed_page().

buf_LRU_block_remove_hashed_page(): Allow bpage->oldest_modification != 0
for uncompressed pages if there is a compressed page that will be preserved.
Release the mutexes before calling buf_print() and buf_LRU_print().

page_zip_validate(): Remove the assertion containing the
buf_frame_get_page_zip() call.  We might already be holding buf_pool->mutex.

successful buf_LRU_free_block().

buf_LRU_free_block(): Note that buf_pool->mutex may be temporarily released.

buf_flush_batch(): Remove the local variable "found".

the buffer pool.

buf_LRU_free_block(): When preserving the compressed page, compute the
checksum.  Also assert page_zip_validate().

buf_zip_decompress(): Add parameter "check" for enabling checksum tests.
Before decompressing a compressed-only page from the buffer pool, verify
the compressed page checksum.

to the buffer pool while we were not holding buf_pool->mutex.  If it was,
do not attempt to preserve the compressed page.

page_zip_malloc(): Replace ut_malloc(...) with mem_heap_alloc(opaque, ...).

page_zip_free(): Dummy function (cannot deallocate from InnoDB memory
heaps, and zlib seems to defer deallocation to the very end anyway).

page_zip_compress(): Create a big enough heap for the needs of zlib.
Replace deflateInit() with deflateInit2().

page_zip_decompress(): Create a big enough heap for the needs of zlib.
Replace inflateInit() with inflateInit2().

Remove the unused parameter init_block.

mem_heap_fast_create(): Remove.

struct mem_block_info_struct: Remove the field init_block.

buf_page_get_gen(): Note that buf_read_page() may uncompress
a compressed-only page.

buf_page_create(): Test buf_page_in_file() instead of BUF_BLOCK_FILE_PAGE.