Cleanup: Make btr_root_block_get() more robust

btr_root_block_get(): Check for index->page == FIL_NULL.

btr_root_get(): Declare static. Other callers can invoke
btr_root_block_get() directly.

btr_get_size(): Remove conditions that are checked in
btr_root_block_get().

storage/innobase/btr/btr0btr.cc

@@ -219,7 +219,7 @@ btr_root_block_get(
 					or RW_X_LATCH */
 	mtr_t*			mtr)	/*!< in: mtr */
 {
-	if (!index->table || !index->table->space) {
+	if (!index->table || !index->table->space || index->page == FIL_NULL) {
 		return NULL;
 	}
 
@@ -259,6 +259,7 @@ btr_root_block_get(
 /**************************************************************//**
 Gets the root node of a tree and sx-latches it for segment access.
 @return root page, sx-latched */
+static
 page_t*
 btr_root_get(
 /*=========*/
@@ -578,10 +579,8 @@ btr_get_size(
 	      || mtr->memo_contains(index->lock, MTR_MEMO_S_LOCK));
 	ut_ad(flag == BTR_N_LEAF_PAGES || flag == BTR_TOTAL_SIZE);
 
-	if (index->page == FIL_NULL
-	    || dict_index_is_online_ddl(index)
-	    || !index->is_committed()
-	    || !index->table->space) {
+	if (dict_index_is_online_ddl(index)
+	    || !index->is_committed()) {
 		return(ULINT_UNDEFINED);
 	}
 

storage/innobase/btr/btr0cur.cc

@@ -411,15 +411,15 @@ static dberr_t btr_cur_instant_init_low(dict_index_t* index, mtr_t* mtr)
 		return DB_CORRUPTION;
 	}
 
-	page_t* root = btr_root_get(index, mtr);
+	buf_block_t* root = btr_root_block_get(index, RW_SX_LATCH, mtr);
 
-	if (!root || btr_cur_instant_root_init(index, root)) {
+	if (!root || btr_cur_instant_root_init(index, root->frame)) {
 		goto unreadable;
 	}
 
 	ut_ad(index->n_core_null_bytes != dict_index_t::NO_CORE_NULL_BYTES);
 
-	if (fil_page_get_type(root) == FIL_PAGE_INDEX) {
+	if (fil_page_get_type(root->frame) == FIL_PAGE_INDEX) {
 		ut_ad(!index->is_instant());
 		return DB_SUCCESS;
 	}

storage/innobase/include/btr0btr.h

@@ -187,16 +187,6 @@ void btr_corruption_report(const buf_block_t* block,const dict_index_t* index);
 	    != index->table->not_redundant())		\
 		btr_corruption_report(block, index)
 
-/**************************************************************//**
-Gets the root node of a tree and sx-latches it for segment access.
-@return root page, sx-latched */
-page_t*
-btr_root_get(
-/*=========*/
-	const dict_index_t*	index,	/*!< in: index tree */
-	mtr_t*			mtr)	/*!< in: mtr */
-	MY_ATTRIBUTE((nonnull));
-
 /**************************************************************//**
 Checks and adjusts the root node of a tree during IMPORT TABLESPACE.
 @return error code, or DB_SUCCESS */

storage/innobase/row/row0purge.cc

@@ -914,7 +914,7 @@ row_purge_upd_exist_or_extern_func(
 
 			index->set_modified(mtr);
 
-			/* NOTE: we must also acquire an X-latch to the
+			/* NOTE: we must also acquire a U latch to the
 			root page of the tree. We will need it when we
 			free pages from the tree. If the tree is of height 1,
 			the tree X-latch does NOT protect the root page,
@@ -923,7 +923,7 @@ row_purge_upd_exist_or_extern_func(
 			latching order if we would only later latch the
 			root page of such a tree! */
 
-			btr_root_get(index, &mtr);
+			btr_root_block_get(index, RW_SX_LATCH, &mtr);
 
 			block = buf_page_get(
 				page_id_t(rseg.space->id, page_no),