send/receive confusion

[edmundo at rano.demon.co.uk]

Sorry, but I'm still confused ...

Both manuals have the same picture which shows a "string dope"
consisting of four components:

 - rcv string
 - rcv string size
 - snd string
 - snd string size

It looks as though the long part of any message (send or receive) may
contain such string dopes.

So, does the message buffer of a send message descriptor contain these
fields called "rcv string" and "rcv string size", and if so, how are
they used?

Also, why does the User Manual say "Specifying send dope values less
than the size dope values makes sense when the caller is willing to
receive more data than it is sending"?

This is referring to the "Message Header" which is apparently found at
the start of the "long part of the message" whose "presense is
indicated by the message descriptor (snd msg/recv msg)". 

So, in the case of a send message descriptor, what is the "size dope
value" used for and why is it there? Similarly, what use is the "send
dope value" in a receive message descriptor?

Edmund


PS. I'm getting this error now when I try to boot Fiasco:

...
DD-L4/x86 microkernel ...
space.cc:179: failed assertion `size == PAGE_SIZE'

I get this on a 686 and one 486 machine, but not on a different 486
machine. I don't know what the significant difference is between the
two 486 machines; there are a lot of differences between them,
including processor manufacturer (Intel?/AMD?) and quantity of memory
(8 MB/32 MB). The 686 machine has a Cyrix processor and 64 MB.