diff --recursive -u orig5037/innobase/include/srv0srv.h mysql-5.0.37/innobase/include/srv0srv.h
--- orig5037/innobase/include/srv0srv.h	2007-03-05 11:21:39.000000000 -0800
+++ mysql-5.0.37/innobase/include/srv0srv.h	2008-10-02 06:10:22.000000000 -0700
@@ -79,6 +79,10 @@
 extern ulint	srv_log_buffer_size;
 extern ulong	srv_flush_log_at_trx_commit;
 
+/* When this event is reset we do not allow any file writes to
+take place. */
+extern os_event_t       srv_allow_writes_event;
+
 extern byte	srv_latin1_ordering[256];/* The sort order table of the latin1
 					character set */
 extern ulint	srv_pool_size;
diff --recursive -u orig5037/innobase/os/os0file.c mysql-5.0.37/innobase/os/os0file.c
--- orig5037/innobase/os/os0file.c	2007-03-05 11:21:03.000000000 -0800
+++ mysql-5.0.37/innobase/os/os0file.c	2008-10-02 06:10:22.000000000 -0700
@@ -518,6 +518,7 @@
 /*========================*/
 			/* out: temporary file handle, or NULL on error */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __NETWARE__
 	FILE*	file	= tmpfile();
 #else /* __NETWARE__ */
@@ -832,6 +833,7 @@
 	ibool		fail_if_exists)	/* in: if TRUE, pre-existing directory
 					is treated as an error. */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL	rcode;
     
@@ -883,6 +885,8 @@
 				OS_FILE_READ_WRITE */
 	ibool*		success)/* out: TRUE if succeed, FALSE if error */
 {
+        if (create_mode != OS_FILE_OPEN && create_mode != OS_FILE_OPEN_RAW)
+                os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	os_file_t	file;
 	DWORD		create_flag;
@@ -1024,6 +1028,8 @@
 				used by a backup program reading the file */
 	ibool*		success)/* out: TRUE if succeed, FALSE if error */
 {
+        if (create_mode != OS_FILE_OPEN && create_mode != OS_FILE_OPEN_RAW)
+                os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	os_file_t	file;
 	DWORD		create_flag;
@@ -1145,6 +1151,8 @@
 	ulint		type,	/* in: OS_DATA_FILE or OS_LOG_FILE */
 	ibool*		success)/* out: TRUE if succeed, FALSE if error */
 {
+        if (create_mode != OS_FILE_OPEN && create_mode != OS_FILE_OPEN_RAW)
+                os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	os_file_t	file;
 	DWORD		share_mode	= FILE_SHARE_READ;
@@ -1359,6 +1367,7 @@
 				/* out: TRUE if success */
 	const char*	name)	/* in: file path as a null-terminated string */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL	ret;
 	ulint	count	= 0;
@@ -1420,6 +1429,7 @@
 				/* out: TRUE if success */
 	const char*	name)	/* in: file path as a null-terminated string */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL	ret;
 	ulint	count	= 0;
@@ -1485,6 +1495,7 @@
 				string */
 	const char*	newpath)/* in: new file path */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL	ret;
 
@@ -1755,6 +1766,7 @@
 				/* out: TRUE if success */
 	FILE*		file)	/* in: file to be truncated */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	HANDLE h = (HANDLE) _get_osfhandle(fileno(file));
 	return(SetEndOfFile(h));
@@ -1772,6 +1784,7 @@
 				/* out: TRUE if success */
 	os_file_t	file)	/* in, own: handle to a file */
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL	ret;
 
@@ -2317,6 +2330,7 @@
 				offset */
 	ulint		n)	/* in: number of bytes to write */	
 {
+        os_event_wait(srv_allow_writes_event);
 #ifdef __WIN__
 	BOOL		ret;
 	DWORD		len;
diff --recursive -u orig5037/innobase/srv/srv0srv.c mysql-5.0.37/innobase/srv/srv0srv.c
--- orig5037/innobase/srv/srv0srv.c	2007-03-05 11:21:12.000000000 -0800
+++ mysql-5.0.37/innobase/srv/srv0srv.c	2008-10-02 06:10:28.000000000 -0700
@@ -115,6 +115,8 @@
 ulint	srv_log_buffer_size	= ULINT_MAX;	/* size in database pages */ 
 ulong	srv_flush_log_at_trx_commit = 1;
 
+os_event_t srv_allow_writes_event;
+
 byte	srv_latin1_ordering[256]	/* The sort order table of the latin1
 					character set. The following table is
 					the MySQL order as of Feb 10th, 2002 */
@@ -951,8 +953,17 @@
 		conc_slot->reserved = FALSE;
 		conc_slot->event = os_event_create(NULL);
 		ut_a(conc_slot->event);
-	}
-}	
+ 	}
+
+        /*
+           Writes have to be enabled on init or else we hang. Thus, we
+           always set the event here regardless of innobase_disallow_writes.
+           That flag will always be 0 at this point because it isn't settable
+           via my.cnf or command line arg.
+        */
+        srv_allow_writes_event = os_event_create(NULL);
+        os_event_set(srv_allow_writes_event);
+}
 
 /*************************************************************************
 Frees the OS fast mutex created in srv_init(). */
diff --recursive -u orig5037/sql/ha_innodb.cc mysql-5.0.37/sql/ha_innodb.cc
--- orig5037/sql/ha_innodb.cc	2007-03-05 11:21:41.000000000 -0800
+++ mysql-5.0.37/sql/ha_innodb.cc	2008-10-02 06:10:28.000000000 -0700
@@ -174,6 +174,7 @@
 my_bool innobase_locks_unsafe_for_binlog        = FALSE;
 my_bool innobase_rollback_on_timeout		= FALSE;
 my_bool innobase_create_status_file		= FALSE;
+my_bool innobase_disallow_writes     = FALSE; /* Must always init to FALSE. */
 
 static char *internal_innobase_data_file_path	= NULL;
 
@@ -7322,4 +7323,17 @@
 						(cursor_view_t*) curview);
 }
 
+/**************************************************************************
+Controls whether InnoDB is in no-write mode. */
+
+void
+innobase_set_disallow_writes(my_bool disallow_writes)
+{
+  ut_a(srv_allow_writes_event);
+  if (disallow_writes)
+    os_event_reset(srv_allow_writes_event);
+  else
+    os_event_set(srv_allow_writes_event);
+}
+
 #endif /* HAVE_INNOBASE_DB */
diff --recursive -u orig5037/sql/ha_innodb.h mysql-5.0.37/sql/ha_innodb.h
--- orig5037/sql/ha_innodb.h	2007-03-05 11:21:41.000000000 -0800
+++ mysql-5.0.37/sql/ha_innodb.h	2008-10-02 06:10:22.000000000 -0700
@@ -216,7 +216,8 @@
                innobase_use_native_aio,
 	       innobase_file_per_table, innobase_locks_unsafe_for_binlog,
 	       innobase_rollback_on_timeout,
-               innobase_create_status_file;
+               innobase_create_status_file,
+               innobase_disallow_writes;
 extern my_bool innobase_very_fast_shutdown; /* set this to 1 just before
 					    calling innobase_end() if you want
 					    InnoDB to shut down without
@@ -334,3 +335,11 @@
 innobase_set_cursor_view(
 /*=====================*/
 	void*	curview);	/* in: Consistent read view to be set */
+
+/***********************************************************************
+Toggle the dynamic option of putting InnoDB into no-write mode. */
+
+void
+innobase_set_disallow_writes(
+/*=========================*/
+        my_bool disallow_writes); /* in: True to turn off writing */
diff --recursive -u orig5037/sql/set_var.cc mysql-5.0.37/sql/set_var.cc
--- orig5037/sql/set_var.cc	2007-03-05 11:21:24.000000000 -0800
+++ mysql-5.0.37/sql/set_var.cc	2008-10-02 06:10:22.000000000 -0700
@@ -116,6 +116,7 @@
 static void fix_thd_mem_root(THD *thd, enum_var_type type);
 static void fix_trans_mem_root(THD *thd, enum_var_type type);
 static void fix_server_id(THD *thd, enum_var_type type);
+static void after_update_disallow_writes(THD *thd, enum_var_type type);
 static KEY_CACHE *create_key_cache(const char *name, uint length);
 void fix_sql_mode_var(THD *thd, enum_var_type type);
 static byte *get_error_count(THD *thd);
@@ -431,6 +432,9 @@
 					     &SV::net_wait_timeout);
 
 #ifdef HAVE_INNOBASE_DB
+sys_var_bool_ptr        sys_innodb_disallow_writes("innodb_disallow_writes",
+                                            &innobase_disallow_writes,
+                                            after_update_disallow_writes);
 sys_var_long_ptr	sys_innodb_fast_shutdown("innodb_fast_shutdown",
 						 &innobase_fast_shutdown);
 sys_var_long_ptr        sys_innodb_max_dirty_pages_pct("innodb_max_dirty_pages_pct",
@@ -777,6 +781,7 @@
   &sys_version_compile_machine,
   &sys_version_compile_os,
 #ifdef HAVE_INNOBASE_DB
+  &sys_innodb_disallow_writes,
   &sys_innodb_fast_shutdown,
   &sys_innodb_max_dirty_pages_pct,
   &sys_innodb_max_purge_lag,
@@ -894,6 +899,8 @@
   {sys_innodb_concurrency_tickets.name, (char*) &sys_innodb_concurrency_tickets, SHOW_SYS},
   {"innodb_data_file_path", (char*) &innobase_data_file_path,	    SHOW_CHAR_PTR},
   {"innodb_data_home_dir",  (char*) &innobase_data_home_dir,	    SHOW_CHAR_PTR},
+  {sys_innodb_disallow_writes.name, (char*) &sys_innodb_disallow_writes,
+                                                                    SHOW_SYS},
   {"innodb_doublewrite", (char*) &innobase_use_doublewrite, SHOW_MY_BOOL},
   {sys_innodb_fast_shutdown.name,(char*) &sys_innodb_fast_shutdown, SHOW_SYS},
   {"innodb_file_io_threads", (char*) &innobase_file_io_threads, SHOW_LONG },
@@ -1426,6 +1433,17 @@
   server_id_supplied = 1;
 }
 
+#ifdef HAVE_INNOBASE_DB
+static void after_update_disallow_writes(THD *thd, enum_var_type type)
+{
+  DBUG_ENTER("after_update_disallow_writes");
+  DBUG_PRINT("info",("innobase_disallow_writes=%d", innobase_disallow_writes));
+
+  innobase_set_disallow_writes(innobase_disallow_writes);
+
+  DBUG_VOID_RETURN;
+}
+#endif
 
 sys_var_long_ptr::
 sys_var_long_ptr(const char *name_arg, ulong *value_ptr,
diff --recursive -u orig5037/sql/set_var.h mysql-5.0.37/sql/set_var.h
--- orig5037/sql/set_var.h	2007-03-05 11:21:22.000000000 -0800
+++ mysql-5.0.37/sql/set_var.h	2008-10-02 06:10:22.000000000 -0700
@@ -142,8 +142,9 @@
 {
 public:
   my_bool *value;
-  sys_var_bool_ptr(const char *name_arg, my_bool *value_arg)
-    :sys_var(name_arg),value(value_arg)
+  sys_var_bool_ptr(const char *name_arg, my_bool *value_arg,
+                   sys_after_update_func after_update_arg= NULL)
+    :sys_var(name_arg, after_update_arg),value(value_arg)
   {}
   bool check(THD *thd, set_var *var)
   {