GINI micro Internet distributor/undistributor

Given a set of remote machine IP addresses, this program will take a
given GINI network and spawn each component on a remote machine. All
network communication between the components should still hold.

command : gdist [options]

Written in Python by Reehan Shaikh
reehan.shaikh@cs.mcgill.ca

Work/change log

January:
	- Proposal approved
	- Started reading all the code of how GINI works in Python,
	  especially since I am familiar with GINI when it was written
	  in C.
	- Mostly reading up on gbuilder, gloader and the classes it
	  depends on.
	- Built a class diagram for the class structure and a very simple
	  sequence diagram to see how messages are passed between the objects.

February:
	- Started working on the actual gdist implementation.
	- Tweaked the options parser so that it reads in an IPFile as well.
	- First step is to be able to use Python to execute shell
	  commands to SSH and SCP into remote machines and execute
	  commands on the remote machine.
	- Am not able to get the proper return value of executing a command on
	  a remote machine via SSH. Searched the Internet for a solution. Fixed
	  this with a Python system call WEXITSTATUS.
	- Extensive reading of how SSH and SCP work, authorized key setup, etc...
	- Continued with gdist implementation.
	- Verification of remote IPs given done.
	- Verification of remote directories done.
	- Proper mapping of components to remote machines done. I had a
	  problem with properly calculating this mapping if there were
	  switches present in the topology, so I introduced the constraint
	  that for gdist, no switches are allowed in the user's topology.

March:
	- Continuing with gdist implementation. A little behind schedule.
	- Spawning of switches on remote machine so that components can
	  communicate with the outside world done. These switches are not
	  topology-specified, they are automatically added so that each
	  component can have a socket ready to communicate to the outside
	  world.
	- Auto-configuring switches done.
	- Starting router and UML components on remote machines done.
	- Auto-configuring these components with shell scripts and batch
	  configuration files done. Problem with running a command to execute
	  a shell script on a remote machine via SSH. SSH hangs until shell
	  script is complete. Not good as these shell scripts start the
	  components, so the script won't finish until the GINI instance is
	  terminated. Very simple solution, execute command on remote machine
	  with "&".
	- BIG PROBLEM: components can't talk to each other. "ping" and "ssh"
	  don't work.
	- Professor Maheswaran and I are too busy at the moment to talk about
	  it.
	- Started implementing gdist undistribute option.

April:
	- Went to see Professor Maheswaran with bug. He found a solution. Bug
	  was in auto-configuring switches. Switches are configured with a port
	  p and a remote IP r. Port p is the port that the switch's socket is
	  listening to on the host machine. Remote IP r is the IP of the remote
	  machine this switch communicates with. But if two switches want to
	  communicate, the switch on the remote IP r must listen on the same
	  port number p. My initial auto-configuration of switches assigned a
	  different port number to every switch, not taking into account this
	  constraint.
	- Everything is working fine now. Components can communicate. Tested
	  "ping" and "ssh". 
	- Tweaked the undistribute option so that user can opt to keep GINI
	  generated files.
	- Started gdist man page. Done.
	- Made last minute minor changes to implementation. This is better
	  understood if you read the code. It is well-commented.
	- Working on HTML page for gdist.