Use my_b_append instead of my_b_write on a SEQ_READ_APPEND cache, when we write

the first 4 bytes of the relay log. Indeed comments in mysys/mf_iocache.c 
say we must always use my_b_append for such a cache.
This *could* avoid a very rare assertion failure which is: 
030524 19:32:38  Slave SQL thread initialized, starting replication in log 'FIRST' at position 0, relay log '/
users/gbichot/4.1.1/mysql-test/var/log/slave-relay-bin.000001' position: 4
030524 19:32:38  next log '/users/gbichot/4.1.1/mysql-test/var/log/slave-relay-bin.000002' is currently active
mysqld: mf_iocache.c:701: _my_b_seq_read: Assertion `pos_in_file == info->end_of_file' failed.
and which seemed to happen always when the SQL thread and/or the I/O thread
were at position 4 in a relay log.


include/my_sys.h:
  moving a function from log_event.cc so that it can be widely used
mysys/mf_iocache.c:
  moving a function from log_event.cc so that it can be widely used
sql/log.cc:
  my_b_write should not be used on a SEQ_READ_APPEND cache, one should use my_b_append
  (otherwise there could be some locking problems).
sql/log_event.cc:
  moved to mysys/mf_iocache.c for wider use.
  A typo.

include/my_sys.h

@@ -677,6 +677,8 @@ extern int _my_b_get(IO_CACHE *info);
 extern int _my_b_async_read(IO_CACHE *info,byte *Buffer,uint Count);
 extern int _my_b_write(IO_CACHE *info,const byte *Buffer,uint Count);
 extern int my_b_append(IO_CACHE *info,const byte *Buffer,uint Count);
+extern int my_b_safe_write(IO_CACHE *info,const byte *Buffer,uint Count);
+
 extern int my_block_write(IO_CACHE *info, const byte *Buffer,
 			  uint Count, my_off_t pos);
 extern int _flush_io_cache(IO_CACHE *info, int need_append_buffer_lock);

mysys/mf_iocache.c

@@ -988,6 +988,20 @@ int my_b_append(register IO_CACHE *info, const byte *Buffer, uint Count)
 }
 
 
+int my_b_safe_write(IO_CACHE *info, const byte *Buffer, uint Count)
+{
+  /*
+    Sasha: We are not writing this with the ? operator to avoid hitting
+    a possible compiler bug. At least gcc 2.95 cannot deal with 
+    several layers of ternary operators that evaluated comma(,) operator
+    expressions inside - I do have a test case if somebody wants it
+  */
+  if (info->type == SEQ_READ_APPEND)
+    return my_b_append(info, Buffer, Count);
+  return my_b_write(info, Buffer, Count);
+}
+
+
 /*
   Write a block to disk where part of the data may be inside the record
   buffer.  As all write calls to the data goes through the cache,

sql/log.cc

@@ -263,7 +263,7 @@ bool MYSQL_LOG::open(const char *log_name, enum_log_type log_type_arg,
 	an extension for the binary log files.
 	In this case we write a standard header to it.
       */
-      if (my_b_write(&log_file, (byte*) BINLOG_MAGIC, BIN_LOG_HEADER_SIZE))
+      if (my_b_safe_write(&log_file, (byte*) BINLOG_MAGIC, BIN_LOG_HEADER_SIZE))
         goto err;
       bytes_written += BIN_LOG_HEADER_SIZE;
       write_file_name_to_index_file=1;

sql/log_event.cc

@@ -26,20 +26,6 @@
 
 #include <assert.h>
 
-inline int my_b_safe_write(IO_CACHE* file, const byte *buf,
-			   int len)
-{
-  /*
-    Sasha: We are not writing this with the ? operator to avoid hitting
-    a possible compiler bug. At least gcc 2.95 cannot deal with 
-    several layers of ternary operators that evaluated comma(,) operator
-    expressions inside - I do have a test case if somebody wants it
-  */
-  if (file->type == SEQ_READ_APPEND)
-    return my_b_append(file, buf,len);
-  return my_b_write(file, buf,len);
-}
-
 #ifdef MYSQL_CLIENT
 static void pretty_print_str(FILE* file, char* str, int len)
 {
@@ -2039,7 +2025,7 @@ Slave: load data infile on table '%s' at log position %s in log \
       err=ER(sql_errno);       
     }
     slave_print_error(rli,sql_errno,"\
-Error '%s' running lOAD DATA INFILE on table '%s'. Default database: '%s'",
+Error '%s' running LOAD DATA INFILE on table '%s'. Default database: '%s'",
 		      err, (char*)table_name, print_slave_db_safe(db));
     free_root(&thd->mem_root,0);
     return 1;