[Evms-devel] EVMS Only Accepts Messages with "corrolator == 0"

[Changju G. <CG...@no...>]

I am working on an ECE plugin. when the plugin is asked by EVMS engine
to
send out a message, the field "corrolator" is always set to 0.
According to the 
document at http://evms.sourceforge.net/clustering/ece_api_guide.txt,
the 
engine should be able to accept a new correlator set by the plugin if
correlaor 
comes in as 0. 

Tests revealed that the engine is still waiting for messages with
"corrolator == 0" 
even if the plugin sets the "corrolator" field to something else.

According to the following code, EVMS puts a talk into the "talk_list"
before asking a 
plugin to send the message out. A plugin can change the "corrolator" of
"talk->say", but
not the entry already in the "talk_list", which will later be used to
screen incoming 
responses (in handle_response()).

So if the "corrolator" field is set by a plugin, EVMS will never get
the response back.
And worse, EVMS can easily mistake a incoming message as a response.
Here is how
that can happen.

Node 1 sends message1 to Node 2. 
Node 2 sands a status message to node 2. 

Node 1 finds the status message "match" message1 in its talk_list
because the status message's 
address is "node 2" and "corrolator==0". In handle_response(), EVMS set
the rc to 0, even after
it realizes that the status message is a request, causing the node1 to
think message1 is replied and
node 2 to wait for the response of the status message that will never
come.


/* Send out the "say" message in the talk_t. */
static int say(talk_t * talk) {

	int rc;
	list_element_t el;

	LOG_PROC_ENTRY();

	talk->got_response = FALSE;

	pthread_mutex_lock(&talk_list_mutex);

	el = insert_thing(&talk_list, talk, INSERT_AFTER, NULL);

	pthread_mutex_unlock(&talk_list_mutex);

	SEND_MSG(&talk->say, rc);

	if (rc != 0) {
		pthread_mutex_lock(&talk_list_mutex);

		delete_element(el);

		pthread_mutex_unlock(&talk_list_mutex);
	}

	LOG_PROC_EXIT_INT(rc);
	return rc;
}




4.2.1.1 Correlator semantics

	ECE facilitates the application with a mechanism to relate
'sent
	messages' with 'messages responded' to the sent messages.

	When a application provides a non-zero correlator, ECE simply
	delivers the correlator to the recipient.  However when a
	application provides a zero correlator, ECE generates a
	correlator and delivers the correlator to the recipient, as
well
	as returns the correlator to the sender.