MDEV-24813 [poc] Signal full table lock when cond is NULL

Will work in the following minimal example

--source include/have_innodb.inc
CREATE TABLE t (a INT PRIMARY KEY) ENGINE=InnoDB;
insert into t values (42);

BEGIN;
SELECT * FROM t LOCK IN SHARE MODE; # will acquire S lock
COMMIT;

DROP TABLE t;

sql/records.cc

@@ -338,8 +338,8 @@ bool init_read_record(READ_RECORD *info,THD *thd, TABLE *table,
   }
   /* Condition pushdown to storage engine */
   if ((table->file->ha_table_flags() & HA_CAN_TABLE_CONDITION_PUSHDOWN) &&
-      select && select->cond && 
-      (select->cond->used_tables() & table->map) &&
+      select && // select->cond &&
+      // (select->cond->used_tables() & table->map) &&
       !table->file->pushed_cond)
     table->file->cond_push(select->cond);
 

storage/innobase/handler/ha_innodb.cc

@@ -2990,6 +2990,7 @@ ha_innobase::ha_innobase(
 			  | HA_CONCURRENT_OPTIMIZE
 			  | HA_CAN_SKIP_LOCKED
 			  |  (srv_force_primary_key ? HA_REQUIRE_PRIMARY_KEY : 0)
+			  | HA_CAN_TABLE_CONDITION_PUSHDOWN
 		  ),
 	m_start_of_scan(),
         m_mysql_has_locked()
@@ -20426,6 +20427,12 @@ ha_innobase::idx_cond_push(
 	DBUG_RETURN(NULL);
 }
 
+const COND*
+ha_innobase::cond_push(const COND *cond)
+{
+  m_prebuilt->full_table_scan|= !cond;
+  return NULL;
+}
 
 /** Push a primary key filter.
 @param[in]	pk_filter	filter against which primary keys

storage/innobase/handler/ha_innodb.h

@@ -403,6 +403,7 @@ class ha_innobase final : public handler
 	@param[in] idx_cond Index condition to be checked
 	@return idx_cond if pushed; NULL if not pushed */
 	Item* idx_cond_push(uint keyno, Item* idx_cond) override;
+  const COND* cond_push(const COND *cond) override;
 	/* @} */
 
 	/** Check if InnoDB is not storing virtual column metadata for a table.

storage/innobase/include/row0mysql.h

@@ -686,6 +686,11 @@ struct row_prebuilt_t {
 	/** The MySQL table object */
 	TABLE*		m_mysql_table;
 
+  bool    full_table_scan; /*!< Whether the full table will need to be
+				  scanned. Set when the sql layer passes NULL cond in
+				  cond_push. Will cause to use X/S locks in select rather than
+				  IX/IS locks */
+
 	/** Get template by dict_table_t::cols[] number */
 	const mysql_row_templ_t* get_template_by_col(ulint col) const
 	{

storage/innobase/row/row0sel.cc

@@ -4714,8 +4714,10 @@ row_search_mvcc(
 		} else {
 wait_table_again:
 			err = lock_table(prebuilt->table, nullptr,
-					 prebuilt->select_lock_type == LOCK_S
-					 ? LOCK_IS : LOCK_IX, thr);
+                       prebuilt->full_table_scan ?
+                       prebuilt->select_lock_type :
+                       (prebuilt->select_lock_type == LOCK_S
+                        ? LOCK_IS : LOCK_IX), thr);
 
 			if (err != DB_SUCCESS) {