MDEV-25361 innochecksum must not report errors for freed pages

Store and maintain xdes pages always. And doesn't verify checksums for
freed pages.

innochecksum can work only with the first space file of multiple ones.
Tell about it and abort in case of not the first file.

extra/innochecksum.cc

@@ -817,6 +817,16 @@ write_file(
 	return(true);
 }
 
+// checks using current xdes page whether the page is free
+static bool page_is_free(const byte *xdes, page_size_t page_size,
+                         size_t page_no)
+{
+  const byte *des=
+      xdes + XDES_ARR_OFFSET +
+      XDES_SIZE * ((page_no & (page_size.physical() - 1)) / FSP_EXTENT_SIZE);
+  return xdes_get_bit(des, XDES_FREE_BIT, page_no % FSP_EXTENT_SIZE);
+}
+
 /*
 Parse the page and collect/dump the information about page type
 @param [in] page	buffer page
@@ -908,11 +918,7 @@ parse_page(
 				std::map<unsigned long long, per_index_stats>::iterator it;
 				it = index_ids.find(id);
 				per_index_stats &index = (it->second);
-				const byte* des = xdes + XDES_ARR_OFFSET
-					+ XDES_SIZE * ((page_no & (page_size.physical() - 1))
-						/ FSP_EXTENT_SIZE);
-				if (xdes_get_bit(des, XDES_FREE_BIT,
-						page_no % FSP_EXTENT_SIZE)) {
+				if (page_is_free(xdes, page_size, page_no)) {
 					index.free_pages++;
 					return;
 				}
@@ -1072,7 +1078,6 @@ parse_page(
 
 	case FIL_PAGE_TYPE_FSP_HDR:
 		page_type.n_fil_page_type_fsp_hdr++;
-		memcpy(xdes, page, page_size.physical());
 		if (page_type_dump) {
 			fprintf(file, "#::%llu\t\t|\t\tFile Space "
 				"Header\t\t|\t%s\n", cur_page_num, str);
@@ -1081,7 +1086,6 @@ parse_page(
 
 	case FIL_PAGE_TYPE_XDES:
 		page_type.n_fil_page_type_xdes++;
-		memcpy(xdes, page, page_size.physical());
 		if (page_type_dump) {
 			fprintf(file, "#::%llu\t\t|\t\tExtent descriptor "
 				"page\t\t|\t%s\n", cur_page_num, str);
@@ -1814,6 +1818,8 @@ int main(
 			printf("page %llu ", cur_page_num);
 		}
 
+		memcpy(xdes, buf, physical_page_size);
+
 		if (page_type_summary || page_type_dump) {
 			parse_page(buf, xdes, fil_page_type, page_size, is_encrypted);
 		}
@@ -1992,6 +1998,7 @@ int main(
 			/* If no-check is enabled, skip the
 			checksum verification.*/
 			if (!no_check
+			    && !page_is_free(xdes, page_size, cur_page_num)
 			    && !skip_page
 			    && (exit_status = verify_checksum(
 						buf, page_size,
@@ -2014,6 +2021,10 @@ int main(
 				printf("page %llu ", cur_page_num);
 			}
 
+			if (page_get_page_no(buf) % physical_page_size == 0) {
+				memcpy(xdes, buf, physical_page_size);
+			}
+
 			if (page_type_summary || page_type_dump) {
 				parse_page(buf, xdes, fil_page_type, page_size, is_encrypted);
 			}