Mach IPC without MiG
                          by Neal H Walfield
                          November 17, 2001

The goal of this exercise is to understand Mach IPC at one of its
lowest application levels.  Thus, you will be generating the
interfaces by hand -- not MiG or another interface generator.  During
the exercise, you will create two threads in a task and send a message
from one, the client, to the other, the server, and have the server
send a response to the client.

What you will learn:

	C Threads: how to create two threads.
	Mach ports: how to allocate send and receive rights
		    (the former implicitly in mach_msg and the latter
		    directly via mach_port_allocate).
	mach_msg: how to send and receive the messages.

The point of keeping both the server and the client in a single task
is to simplify the implementation: there is no need to try to register
the server with a central name server nor communicate the identifier
to the client: this is another exercise in and of itself.

As such, it is recommended that you initially create a single receive
right and store it in a global variable accessible to both the client
and server threads.

The following interface should be implemented:

	routine hello (name: string_t;
		       out message: string_t);

Which is to say, the client should send his name to the server and the
server should reply by sending another string containing: "Hello, %s!"
where the `%s' is substituted by the contents of name.

The following resources will be of value:

	Mach 3 Kernel Principles [1]
		Chapters 2: Architectural Model

	Mach 3 Kernel Interfaces [1]
		mach_msg: page 5
                mach_port_allocate: page 39
		mach_msg_header_t: page 327
		mach_msg_type_t: page 330

	Mach 3 Server's Guide [1]
		Chaper 5: C Threads

Inline messages have the following general structure:

 [ [mach_msg_header_t] [[mach_msg_type_t][data]] [[mach_msg_type_t][data]]... ]
 ^ ^                   ^^                ^       ^
 | |                   ||                |       \- Second set of arguments
 | |                   ||                \- First set of arguments
 | \- Message header   |\- Header for first set of arguments
 \- Message            \- Pay load

When data is marked out of line, the data section is detached.


Estimated length of project: 20-40 hours for someone who knows C and
Unix but is a beginner to Mach.


[1] ftp://ftp.cs.cmu.edu/afs/cs/project/mach/public/doc/osf