MDEV-39092 BACKUP SERVER of ENGINE=Aria to the local file system

Add MTR test. Copy MyISAM files in Aria plugin so that the MTR works.
Perform the end step under maximum level of backup MDL to safely copy
non-transactional Aria and MyISAM files.

Author: mariadb-andrzejjarzabek

mysql-test/main/backup_server_restore.result

@@ -0,0 +1,41 @@
+Prepare database
+CREATE TABLE tinno (i INTEGER) ENGINE=InnoDB;
+INSERT INTO tinno VALUES (1), (2), (3), (4);
+CREATE TABLE tariatr (i INTEGER) ENGINE=Aria TRANSACTIONAL=1;
+INSERT INTO tariatr VALUES (2), (3), (5), (7);
+CREATE TABLE tariant (i INTEGER) ENGINE=Aria TRANSACTIONAL=0;
+INSERT INTO tariant VALUES (1), (1), (2), (3), (5);
+Back up the database
+BACKUP SERVER TO '$MYSQLTEST_VARDIR/some_directory';
+Restore the database
+# restart: --datadir=MYSQLTEST_VARDIR/some_directory
+Check contents after restore
+SELECT * FROM tinno;
+i
+1
+2
+3
+4
+SELECT * FROM tariatr;
+i
+2
+3
+5
+7
+SELECT * FROM tariant;
+i
+1
+1
+2
+3
+5
+Warnings:
+Error	145	Got error '145 "Table was marked as crashed and should be repaired"' for './test/tariant'
+Warning	1034	1 client is using or hasn't closed the table properly
+Note	1034	Table is fixed
+Restart database in original data directory 
+# restart
+Clean up
+DROP TABLE tinno;
+DROP TABLE tariatr;
+DROP TABLE tariant;

mysql-test/main/backup_server_restore.test

@@ -0,0 +1,38 @@
+--source include/not_windows.inc
+--source include/have_innodb.inc
+
+--echo Prepare database
+CREATE TABLE tinno (i INTEGER) ENGINE=InnoDB;
+INSERT INTO tinno VALUES (1), (2), (3), (4);
+CREATE TABLE tariatr (i INTEGER) ENGINE=Aria TRANSACTIONAL=1;
+INSERT INTO tariatr VALUES (2), (3), (5), (7);
+CREATE TABLE tariant (i INTEGER) ENGINE=Aria TRANSACTIONAL=0;
+INSERT INTO tariant VALUES (1), (1), (2), (3), (5);
+
+--echo Back up the database
+evalp BACKUP SERVER TO '$MYSQLTEST_VARDIR/some_directory';
+
+--echo Restore the database
+--disable_query_log
+call mtr.add_suppression("InnoDB: Did not find any checkpoint after LSN=");
+call mtr.add_suppression("InnoDB: Renaming ib_[0-9]+.log to ib_logfile0");
+call mtr.add_suppression("mariadbd: Got error '145 \"Table was marked as crashed and should be repaired\"' for ");
+call mtr.add_suppression("Checking table: ");
+--enable_query_log
+--let $restart_parameters=--datadir=$MYSQLTEST_VARDIR/some_directory
+--source include/restart_mysqld.inc
+
+--echo Check contents after restore
+SELECT * FROM tinno;
+SELECT * FROM tariatr;
+SELECT * FROM tariant;
+
+--echo Restart database in original data directory 
+--let $restart_parameters=
+--source include/restart_mysqld.inc
+
+--echo Clean up
+DROP TABLE tinno;
+DROP TABLE tariatr;
+DROP TABLE tariant;
+--rmdir $MYSQLTEST_VARDIR/some_directory

sql/sql_backup.cc

@@ -274,11 +274,15 @@ bool Sql_cmd_backup::execute(THD *thd)
                                    MYSQL_STORAGE_ENGINE_PLUGIN,
                                    PLUGIN_IS_DELETED|PLUGIN_IS_READY, nullptr);
 
-  /* FIXME: Escalate to MDL_BACKUP_BLOCK_DDL or similar */
-  fail=
-    plugin_foreach_with_mask(thd, backup_end, MYSQL_STORAGE_ENGINE_PLUGIN,
-                             PLUGIN_IS_DELETED|PLUGIN_IS_READY,
-                             reinterpret_cast<void*>(fail)) || fail;
+  if(!thd->mdl_context.upgrade_shared_lock(mdl_request.ticket,
+                                           MDL_BACKUP_WAIT_COMMIT,
+                                           thd->variables.lock_wait_timeout))
+    fail=
+      plugin_foreach_with_mask(thd, backup_end, MYSQL_STORAGE_ENGINE_PLUGIN,
+                               PLUGIN_IS_DELETED|PLUGIN_IS_READY,
+                               reinterpret_cast<void*>(fail)) || fail;
+  else
+    fail= true;
 
   /* The final part must not interfere with the use of the server datadir.
   Release the locks. */

storage/maria/ma_backup.cc

@@ -332,8 +332,10 @@ namespace
 #endif
   };
 
-  /* TODO: .frm failes are nto Aria-specific, they are copied here as a stop-gap */
-  const std::vector<std::string> Aria_backup::data_exts {".MAD"s, ".MAI"s, ".frm"s};
+  /* TODO: .frm failes are not Aria-specific, .MYD and .MYI are MyISAM files;
+   they are copied here as a stop-gap */
+  const std::vector<std::string>
+    Aria_backup::data_exts {".MAD"s, ".MAI"s, "MYD"s, "MYI"s, "frm"s};
   const std::string Aria_backup::log_file_prefix {"aria_log."};
 
   std::unique_ptr<Aria_backup> aria_backup;