MDEV-23986: fil_page_type_validate() fails on crash recovery

In MDEV-12353, we changed the redo log format so that whenever
any data field is changed, the unchanged prefix of the bytes
will by default be omitted from the redo log record.

However, in order for the MDEV-23199 logic to work, changes of
FSP_SPACE_FLAGS must always be written in full (mtr_t::FORCED),
so that crash recovery can parse them. We must know the flags
in advance, because we might be applying log to other pages than
page 0 first.

recv_scan_log_recs(): Correct a misleading message about starting
crash recovery. Display both the checkpoint LSN and the start
of the records that end in the FILE_CHECKPOINT marker.

Reviewed by: Thirunarayanan Balathandayuthapani

storage/innobase/fil/fil0fil.cc

@@ -3567,8 +3567,9 @@ void fsp_flags_try_adjust(fil_space_t* space, ulint flags)
 				<< " to " << ib::hex(flags);
 		}
 		mtr.set_named_space(space);
-		mtr.write<4>(*b, FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
-			     + b->frame, flags);
+		mtr.write<4,mtr_t::FORCED>(*b,
+					   FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
+					   + b->frame, flags);
 	}
 func_exit:
 	mtr.commit();

storage/innobase/fsp/fsp0fsp.cc

@@ -582,10 +582,11 @@ void fsp_header_init(fil_space_t* space, uint32_t size, mtr_t* mtr)
 				   + block->frame, size);
 	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT
 				    + block->frame));
-	mtr->write<4,mtr_t::MAYBE_NOP>(*block,
-				       FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
-				       + block->frame,
-				       space->flags & ~FSP_FLAGS_MEM_MASK);
+	if (auto f = space->flags & ~FSP_FLAGS_MEM_MASK) {
+		mtr->write<4,mtr_t::FORCED>(*block,
+					    FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
+					    + block->frame, f);
+	}
 	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FRAG_N_USED
 				    + block->frame));
 

storage/innobase/handler/handler0alter.cc

@@ -10316,13 +10316,15 @@ commit_cache_norebuild(
 					    page_id_t(space->id, 0),
 					    space->zip_size(),
 					    RW_X_LATCH, &mtr)) {
-					mtr.set_named_space(space);
-					mtr.write<4,mtr_t::MAYBE_NOP>(
-						*b,
-						FSP_HEADER_OFFSET
-						+ FSP_SPACE_FLAGS + b->frame,
-						space->flags
-						& ~FSP_FLAGS_MEM_MASK);
+					byte* f = FSP_HEADER_OFFSET
+						+ FSP_SPACE_FLAGS + b->frame;
+					const auto sf = space->flags
+						& ~FSP_FLAGS_MEM_MASK;
+					if (mach_read_from_4(f) != sf) {
+						mtr.set_named_space(space);
+						mtr.write<4,mtr_t::FORCED>(
+							*b, f, sf);
+					}
 				}
 				mtr.commit();
 			}

storage/innobase/log/log0recv.cc

@@ -2929,8 +2929,8 @@ static bool recv_scan_log_recs(
 				}
 
 				ib::info() << "Starting crash recovery from"
-					" checkpoint LSN="
-					<< recv_sys.scanned_lsn;
+					" checkpoint LSN=" << checkpoint_lsn
+					   << "," << recv_sys.scanned_lsn;
 			}
 
 			/* We were able to find more log data: add it to the