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.

1 files changed, 14 insertions, 0 deletions

diff --git a/mysys/mf_iocache.c b/mysys/mf_iocache.c
index 0f35ee048bb..d96d4c0db3c 100644
--- a/mysys/mf_iocache.c
+++ b/mysys/mf_iocache.c
@@ -988,6 +988,20 @@ end:
 }
 
 
+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,