Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB

previous correction didn't. make sure "tail" is fixed up
when filling cache several times; rework formulae.
---
Merge sin.intern.azundris.com:/home/tnurnberg/22540/50-22540
into  sin.intern.azundris.com:/home/tnurnberg/22540/51-22540

mysql-test/extra/binlog_tests/binlog.test

@@ -5,7 +5,6 @@
 -- source include/have_log_bin.inc
 -- source include/not_embedded.inc
 -- source include/have_innodb.inc
--- source include/have_log_bin.inc
 -- source include/have_debug.inc
 
 --disable_warnings
@@ -139,6 +138,36 @@ show binlog events from 0;
 
 set session autocommit = @ac;
 
+# now show that nothing breaks if we need to read from the cache more
+# than once, resulting in split event-headers
+
+set @bcs = @@binlog_cache_size;
+set @ac = @@autocommit;
+
+set global binlog_cache_size=4096;
+set autocommit= 0;
+reset master;
+
+create table t1 (a int) engine=innodb;
+
+let $1=400;
+disable_query_log;
+begin;
+while ($1)
+{
+ eval insert into t1 values( $1 );
+ dec $1;
+}
+commit;
+enable_query_log;
+
+show binlog events from 0;
+
+drop table t1;
+
+set global binlog_cache_size=@bcs;
+set session autocommit = @ac;
+
 --echo End of 5.0 tests
 
 # Test of a too big SET INSERT_ID: see if the truncated value goes

mysql-test/r/rpl_row_create_table.result

@@ -279,25 +279,25 @@ Log_name	Pos	Event_type	Server_id	End_log_pos	Info
 #	192	Table_map	#	231	table_id: # (test.t1)
 #	231	Write_rows	#	275	table_id: # flags: STMT_END_F
 #	275	Query	#	343	use `test`; BEGIN
-#	343	Query	#	125	use `test`; CREATE TABLE `t2` (
+#	343	Query	#	468	use `test`; CREATE TABLE `t2` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=InnoDB
-#	468	Table_map	#	164	table_id: # (test.t2)
-#	507	Write_rows	#	208	table_id: # flags: STMT_END_F
+#	468	Table_map	#	507	table_id: # (test.t2)
+#	507	Write_rows	#	551	table_id: # flags: STMT_END_F
 #	551	Xid	#	578	COMMIT /* XID */
 #	578	Query	#	646	use `test`; BEGIN
-#	646	Query	#	125	use `test`; CREATE TABLE `t3` (
+#	646	Query	#	771	use `test`; CREATE TABLE `t3` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=InnoDB
-#	771	Table_map	#	164	table_id: # (test.t3)
-#	810	Write_rows	#	208	table_id: # flags: STMT_END_F
+#	771	Table_map	#	810	table_id: # (test.t3)
+#	810	Write_rows	#	854	table_id: # flags: STMT_END_F
 #	854	Xid	#	881	COMMIT /* XID */
 #	881	Query	#	949	use `test`; BEGIN
-#	949	Query	#	125	use `test`; CREATE TABLE `t4` (
+#	949	Query	#	1074	use `test`; CREATE TABLE `t4` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=InnoDB
-#	1074	Table_map	#	164	table_id: # (test.t4)
-#	1113	Write_rows	#	208	table_id: # flags: STMT_END_F
+#	1074	Table_map	#	1113	table_id: # (test.t4)
+#	1113	Write_rows	#	1157	table_id: # flags: STMT_END_F
 #	1157	Xid	#	1184	COMMIT /* XID */
 #	1184	Table_map	#	1223	table_id: # (test.t1)
 #	1223	Write_rows	#	1267	table_id: # flags: STMT_END_F
@@ -371,10 +371,10 @@ Log_name	Pos	Event_type	Server_id	End_log_pos	Info
 #	231	Write_rows	#	275	table_id: # flags: STMT_END_F
 #	275	Query	#	375	use `test`; CREATE TABLE t2 (a INT) ENGINE=INNODB
 #	375	Query	#	443	use `test`; BEGIN
-#	443	Table_map	#	39	table_id: # (test.t2)
-#	482	Write_rows	#	83	table_id: # flags: STMT_END_F
-#	526	Table_map	#	122	table_id: # (test.t2)
-#	565	Write_rows	#	161	table_id: # flags: STMT_END_F
+#	443	Table_map	#	482	table_id: # (test.t2)
+#	482	Write_rows	#	526	table_id: # flags: STMT_END_F
+#	526	Table_map	#	565	table_id: # (test.t2)
+#	565	Write_rows	#	604	table_id: # flags: STMT_END_F
 #	604	Xid	#	631	COMMIT /* XID */
 SELECT * FROM t2 ORDER BY a;
 a
@@ -396,7 +396,7 @@ SELECT * FROM t2 ORDER BY a;
 a
 SHOW BINLOG EVENTS FROM 631;
 Log_name	Pos	Event_type	Server_id	End_log_pos	Info
-#	631	Query	#	80	use `test`; TRUNCATE TABLE t2
+#	631	Query	#	711	use `test`; TRUNCATE TABLE t2
 #	711	Xid	#	738	COMMIT /* XID */
 SELECT * FROM t2 ORDER BY a;
 a

sql/log.cc

@@ -3995,30 +3995,24 @@ int MYSQL_BIN_LOG::write_cache(IO_CACHE *cache, bool lock_log, bool sync_log)
       memcpy((char *)cache->read_pos, &header[carry], LOG_EVENT_HEADER_LEN - carry);
 
       /* next event header at ... */
-      hdr_offs = LOG_EVENT_HEADER_LEN - carry +
-        uint4korr(&header[EVENT_LEN_OFFSET]);
+      hdr_offs = uint4korr(&header[EVENT_LEN_OFFSET]) - carry;
 
       carry= 0;
     }
 
     /* if there is anything to write, process it. */
 
-    if(likely(bytes > 0))
+    if (likely(bytes > 0))
     {
       /*
-        next header beyond current read-buffer? we'll get it later
-        (though not necessarily in the very next iteration).
+        process all event-headers in this (partial) cache.
+        if next header is beyond current read-buffer,
+        we'll get it later (though not necessarily in the
+        very next iteration, just "eventually").
       */
 
-      if (hdr_offs >= bytes)
-        hdr_offs -= bytes;
-      else
+      while (hdr_offs < bytes)
       {
-
-        /* process all event-headers in this (partial) cache. */
-
-        do {
-
         /*
           partial header only? save what we can get, process once
           we get the rest.
@@ -4045,8 +4039,17 @@ int MYSQL_BIN_LOG::write_cache(IO_CACHE *cache, bool lock_log, bool sync_log)
           hdr_offs += uint4korr(log_pos);
 
         }
-        } while (hdr_offs < bytes);
       }
+
+      /*
+        Adjust hdr_offs. Note that this doesn't mean it will necessarily
+        be valid in the next iteration; if the current event is very long,
+        it may take a couple of read-iterations (and subsequent fixings
+        of hdr_offs) for it to become valid again.
+        if we had a split header, hdr_offs was already fixed above.
+      */
+      if (carry == 0)
+        hdr_offs -= bytes;
     }
 
     /* Write data to the binary log file */