messaging questions...

[David Leimbach]

I am still intrigued and slightly confused by the messaging system

"The messaging API will wrap this basic mechanism into synchronous and 
asynchronous messaging functions. For example, lwkt_domsg() will send a 
message synchronously and wait for a reply. It will set a flag to hint 
to the target port that the message will be blocked on synchronously 
and if the target port returns EASYNC, lwkt_domsg() will block. 
Likewise lwkt_sendmsg() would send a message asynchronously, but if the 
target port returns a synchronous error code (i.e. anything not EASYNC) 
lwkt_sendmsg() will manually queue the now complete message on the 
reply port itself."

Here is how I interpretted the above:

lwkt_domsg() sends a synchronous message waiting for some kind of 
reply.  If we get EASYNC from the target we block.  What if we don't 
get EASYNC?

lwkt_sendmsg() sends an asynchronous message but if the port returns 
anything that isn't EASYNC lwkt_sendmessage will queue its
whole message on the reply port.

What do you mean by "now complete"?  If it sends asynchronously why 
would it send an incomplete asynchrounous message?  Also I would think 
that EASYNC would imply that some error occurred while trying to do 
something asynchronous.  I don't understand the rationale for the
name.

Perhaps a state transition diagram of some kind or a flow chart or 
something would help me visualize what is being said. :)

I think I understand the part about mp_SendMsg() working with the 
message as it came in synchronously without telling
the message originator to "go away... I'll get it later".

"User<->Kernel messaging interfaces simply employ mp_SendMsg() function 
vectors which do the appropriate translation, so as far as the sender 
and recipient are concerned the message will be local to their VM 
context."

I presume these vectors are how the system call interface is 
implemented via messages?

Still trying to understand :).  One day I will try to run this at home 
again.

Dave