Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

Add two-way communication between parent and child in wsp::proc class.
Refactor wsp::thd class to call my_thread_init() conditionally.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

If mariabackup does not get the password on command line or from
the [mariabackup] section of the config file, it initializes the
internal opt_password variable to empty string and considers it
as set in a subsequent check, therefore ignoring the value of
MYSQL_PWD envronment variable. At the same time MariDB server
considers empty string passwords as no password.

Fixing this is necessary to use automatically generated SST users
because mariabackup needs --default-file option to use the same
config as the server and that option does not allow to supply any
extra config files, so using the automatically generated config
with [mariabackup] section is out of question.

Modify check for set password to treat empty string as unset
and fall back to the MYSQL_PWD value if present.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

		tablespace truncation

- InnoDB fails with out of bound write error after temporary
tablespace truncation. This issue caused by
commit c507678b (MDEV-28699).
InnoDB fail to clear freed ranges if shrinking size
is the last offset of the freed range.

Now that we do not pollute systemd's environment but write private
environment files running these as root is not longer required. So
let's drop `PermissionsStartOnly=true`.

Debian adds extra `ExecStartPre=` and `ExecStartPost=`, though.
Use special executable prefix for full privileges there. (See
systemd.service(5) for details.)

Support in service file was dropped in 91f16948
(systemd: multi-instance not for Galera, User/Group flexible).

Now that the systemd unit files use an environment file to pass
_WSREP_START_POSITION we have to update galera_new_cluster as well.

We used to run `systemctl set-environment` to pass
_WSREP_START_POSITION. This is bad because:

* it clutter systemd's environment (yes, pid 1)
* it requires root privileges
* options (like LimitNOFILE=) are not applied

Let's just create an environment file in ExecStartPre=, that is read
before ExecStart= kicks in. We have _WSREP_START_POSITION around for the
main process without any downsides.

mysqldump --dir produces unexpected sql output on stdout.
All sql should go into .sql files (and data to .txt files)

A cleanup for MDEV-25829.

Using /WX (warning as error) during configuration step caused
HAVE_OPENSSL_APPLINK_C to be OFF

This made client utilities fail with "Applink not found" during runtime.

Hardcode -DHAVE_OPENSSL_APPLINK_C=1 for CMake for now, fix connector
later.

* show it as a datetime, not number of seconds
* show all users
* show manually expired users as 0000-00-00 00:00:00
* show default expiration interval correctly
* numerous test fixes, add more tests
* fix compilation of embedded

* A new table INFORMATION_SCHEMA.USERS is introduced.
* It stores auxiliary user data
* An unprivileged user can access their own data, and that is the main
  difference with what mysql.global_priv provides
* The fields are currently: USER, PASSWORD_ERRORS, PASSWORD_EXPIRATION_TIME
* If password_errors is ignored for the user, PASSWORD_ERRORS is NULL
* PASSWORD_EXPIRATION_TIME is a timestamp with exact point in time, calculated
from password_last_changed and password_lifetime (i.e. days) stored for the user

Columns added to TABLE_STATISTICS
- ROWS_INSERTED, ROWS_DELETED, ROWS_UPDATED, KEY_READ_HITS and
  KEY_READ_MISSES.

Columns added to CLIENT_STATISTICS and USER_STATISTICS:
- KEY_READ_HITS and KEY_READ_MISSES.

User visible changes (except new columns):
- CLIENT_STATISTICS and USER_STATISTICS has columns KEY_READ_HITS and
  KEY_READ_MISSES added after column ROWS_UPDATED before SELECT_COMMANDS.

Other changes:
- Do not collect table statistics for system tables like index_stats
  table_stats, performance_schema, information_schema etc as the user
  has no control of these and the generate noice in the statistics.
- All row variables that are part of user_stats are moved to
  'struct rows_stats' to make it easy to clear all of them at once.
- ha_read_key_misses added to STATUS_VAR

Notes:
- userstat.result has a change of numbers of rows for handler_read_key.
  This is because use-stat-tables is now disabled for the test.

fixes a failure of period.create on bintar-centos74-amd64

EE_ numbers occupy the same range as OS Exxx errors and
my_errno is generally for OS errors. And for HA_ERR_ handler errors
which occupy a different range, so can be freely mixed with OS errors.

add a test case

reinit_io_cache() resets and restores MY_TRACK_WITH_LIMIT internally

and make it static

and rephrase memory accounting error message to match tmp_space one
(besides, memory accounting error could - and did - happen when all
memory was actually freed)

MDEV-34150 Assertion failure in Diagnostics_area::set_error_status upon binary logging hitting tmp space limit

- Moved writing to binlog_cache from close_thread_tables() to
  binlog_commit().
- In select_create() delete cached row events instead of flushing them
  to disk. This was done to avoid possible disk write error in this code.

MDEV-34054 Memory leak in Window_func_runner::exec after encountering "temporary space limit reached" error

Changes:
- Fixed that MyISAM and Aria parallel repair works with tmp file limit.
  This required to add current_thd to all parallel workers and add
  protection in my_malloc_size_cb_func() and temp_file_size_cb_func() to
  be able to handle shared THD's.  I removed the old code in MyISAM to
  set current_thd() as only worked when using with virtal indexed
  columns and I wanted to keep the Aria and MyISAM code identical.

Other things:
- Improved error messages from Aria parallel repair and
  create_internal_tmp_table_from_heap().

The bug was that Aggregator_distinct::add() did not properly handle
write errors. (Old bug exposed by the new code).

Two new variables added:
- max_tmp_space_usage : Limits the the temporary space allowance per user
- max_total_tmp_space_usage: Limits the temporary space allowance for
  all users.

New status variables: tmp_space_used & max_tmp_space_used
New field in information_schema.process_list: TMP_SPACE_USED

The temporary space is counted for:
- All SQL level temporary files. This includes files for filesort,
  transaction temporary space, analyze, binlog_stmt_cache etc.
  It does not include engine internal temporary files used for repair,
  alter table, index pre sorting etc.
- All internal on disk temporary tables created as part of resolving a
  SELECT, multi-source update etc.

Special cases:
- When doing a commit, the last flush of the binlog_stmt_cache
  will not cause an error even if the temporary space limit is exceeded.
  This is to avoid giving errors on commit. This means that a user
  can temporary go over the limit with up to binlog_stmt_cache_size.

Noteworthy issue:
- One has to be careful when using small values for max_tmp_space_limit
  together with binary logging and with non transactional tables.
  If a the binary log entry for the query is bigger than
  binlog_stmt_cache_size and one hits the limit of max_tmp_space_limit
  when flushing the entry to disk, the query will abort and the
  binary log will not contain the last changes to the table.
  This will also stop the slave!
  This is also true for all Aria tables as Aria cannot do rollback
  (except in case of crashes)!
  One way to avoid it is to use @@binlog_format=statement for
  queries that updates a lot of rows.

Implementation:
- All writes to temporary files or internal temporary tables, that
  increases the file size, are routed through temp_file_size_cb_func()
  which updates and checks the temp space usage.
- Most of the temporary file monitoring is done inside IO_CACHE.
  Temporary file monitoring is done inside the Aria engine.
- MY_TRACK and MY_TRACK_WITH_LIMIT are new flags for ini_io_cache().
  MY_TRACK means that we track the file usage. TRACK_WITH_LIMIT means
  that we track the file usage and we give an error if the limit is
  breached. This is used to not give an error on commit when
  binlog_stmp_cache is flushed.
- global_tmp_space_used contains the total tmp space used so far.
  This is needed quickly check against max_total_tmp_space_usage.
- Temporary space errors are using EE_LOCAL_TMP_SPACE_FULL and
  handler errors are using HA_ERR_LOCAL_TMP_SPACE_FULL.
  This is needed until we move general errors to it's own error space
  so that they cannot conflict with system error numbers.
- Return value of my_chsize() and mysql_file_chsize() has changed
  so that -1 is returned in the case my_chsize() could not decrease
  the file size (very unlikely and will not happen on modern systems).
  All calls to _chsize() are updated to check for > 0 as the error
  condition.
- At the destruction of THD we check that THD::tmp_file_space == 0
- At server end we check that global_tmp_space_used == 0
- As a precaution against errors in the tmp_space_used code, one can set
  max_tmp_space_usage and max_total_tmp_space_usage to 0 to disable
  the tmp space quota errors.
- truncate_io_cache() function added.
- Aria tables using static or dynamic row length are registered in 8K
  increments to avoid some calls to update_tmp_file_size().

Other things:
- Ensure that all handler errors are registered.  Before, some engine
  errors could be printed as "Unknown error".
- Fixed bug in filesort() that causes a assert if there was an error
  when writing to the temporay file.
- Fixed that compute_window_func() now takes into account write errors.
- In case of parallel replication, rpl_group_info::cleanup_context()
  could call trans_rollback() with thd->error set, which would cause
  an assert. Fixed by resetting the error before calling trans_rollback().
- Fixed bug in subselect3.inc which caused following test to use
  heap tables with low value for max_heap_table_size
- Fixed bug in sql_expression_cache where it did not overflow
  heap table to Aria table.
- Added Max_tmp_disk_space_used to slow query log.
- Fixed some bugs in log_slow_innodb.test