Tests with 4096-byte sector size confirm that it is
safe to use O_DIRECT with page_compressed tables.
That had been disabled on Linux, in an attempt to fix MDEV-21584
which had been filed for the O_DIRECT problems earlier.
The fil_node_t::block_size was being set mostly correctly until
commit 10dd290b4b (MDEV-17380)
introduced a regression in MariaDB Server 10.4.4.
fil_node_open_file(): Only avoid setting O_DIRECT on
ROW_FORMAT=COMPRESSED tables that use KEY_BLOCK_SIZE=1 or 2
(1024 or 2048 bytes).
fil_ibd_create(): Avoid setting O_DIRECT on ROW_FORMAT=COMPRESSED tables
that use KEY_BLOCK_SIZE=1 or 2 (1024 or 2048 bytes).
fil_node_t::find_metadata(): Require fstat() to be always invoked
outside Microsoft Windows, so that fil_node_t::block_size can be set.
fil_node_t::read_page0(): Rely on find_metadata() to assign block_size.
Thanks to Vladislav Vaintroub for testing this on Microsoft Windows
using an old-fashioned rotational hard disk with 4KiB sector size.
Reviewed by: Vladislav Vaintroub
This is a port of commit 00f620b27e
and commit 6505662c23 from 10.2.
126725421e