Nachos Network

Each running Nachos is a node in the network, this node is emulated as a UNIX process; a network provides the communication between those nodes, these networks are emulated by UNIX sockets.

We can try this by running 'nachos -m 0 -o 1' and 'nachos -m 1 -o 0'simultaneously, in two different terminals. For this, you need implamantation of locks and condition variables.

For now, I'm just explaining nachos' network code.

nettest.cc

MailTest : Function for test out message delivery.

farAddr : machine's ID, to wich we are sending the message.

outPktHdr, OutMailHdr : Outcoming message properties.

inPktHdr, inMailHdr : Incoming message properties.

const char *data = "Hello there" : Message that we are sendig to the other machin, at mailbox #0.

const char *ack = "Got it" : This is gonna be the acknowledgment of receiving the message.

MaxMailSize: Maximum real data that a message can include. (defined in post.cc)

outPktHdr.to = radAddr / outMailHdr.to = 0: Destination machin. Its mailbox it's mailbox #0

outMailHdr.from: Machine that is sending the message. Reply to mailbox #1

outMailHdr.length = strlen(data) + 1: measuring message size ("Hello there!")

postOffice->Send: Sending first message.

postOffice->Receive : Waiting message from the other machine.

0, &inPktHdr, &inMailHdr, buffer: incoming mesagge properties.

fflush(stdout): cleaning output buffer.

Machine is going to know were te incoming message is coming from (inPktHdr.from, inMailHdr.from)

Then it is sending the acknowledgment to the other machine (outPktHdr.to , outMail.Hdr.to)

The size of the outgoing message is measured by outMailHdr.lenght = strleng(ack) +1

Sending the ack: postOffice->Send

Waiting the ack of the second machin from the first sended message.

Done!

----------------------------------------------------------------------

post.cc

This is where we are going to storage our messages.

to: destination mailbox.
from: Where we are going to reply the message.
length: size of the message. Size cannot be negative.

Maximum data that a message can include.

The format of a message we send/recieve is by layers:
- Network Header (PacketHeader)
- Post Office Header (MailHeader)

- data

This class define this format.

Mail ( PacketHeader pktH , MailHeader mailH , const char *msgData ) : concatenate headers to data.

char data[MaxMailSize]: message data. Array of MAXMAILSIZE size.

This class defines the place where we are going to storage the messages.

Mailbox() : Allocate and initialize mail box
~Mailbox() : De-allocate mail box.


SynchList<Mail*> *messages : A mailbox is a list of messages.

Post Office is a collection of mailboxes. This class defines a Post Office.

PostOffice : allocate and initalizate.

De-allocate.

Send a message to the other machine mailbox.

Retrieve the ack.

Wait incoming message. Put them in the correct mailbox.

Interrupt Handler: Next packet can now be sent.

Interrupt Handler: incoming message has arrived.

---------------------------------------------------------------------

These are the files that nettest.cc includes.

Sockets implementation: Client

#include 
#include 
#include    

#define SERVER_PORT 9999  

these are the libraries which define socket and the internet socket also a server port.

if( ( hp = gethostbyname( argv[1] ) ) == NULL )
{
printf( "%s: %s unknown host\n", argv[0], argv[1] );
exit( 1 );
}
bcopy( hp->h_addr_list[0], (char*)&server_addr.sin_addr, hp->h_length );

this part of code gets the host and if it doesn't get it print a error message

if( ( sd = socket( AF_INET, SOCK_STREAM, 0 ) ) == -1 )
{
perror( "client: socket failed" );
exit( 1 );
}
if( connect( sd, (struct sockaddr*)&server_addr,
 sizeof(server_addr) ) == -1 )
{
perror( "client: connect FAILED:" );
exit( 1 );
}

printf("connect() successful! will send a message to server\n");
printf("Input a string:\n" );

while( scanf( "%s", buf) != EOF)
{
 write(sd, buf, sizeof(buf));
  read(sd, buf, sizeof(buf));
  printf("SERVER ECHOED: %s\n", buf);
}

hier the socket is created and conected with the client and server



Sockets implementation: Server

if( listen( sd, 1 ) == -1 )
{
perror( "server: listen failed" );
exit( 1 );
}

printf("SERVER is listening for clients to establish a connection\n");

if( ( ns = accept( sd, (struct sockaddr*)&client_addr,
                   &client_len ) ) == -1 )
{
    perror( "server: accept failed" );
    exit( 1 );
}

printf("accept() successful.. a client has connected! waiting for a message\n");

the server is listenig for clients and if is conected successfuly then you can write the message....

OUTPUT

Sources:

http://www.dreamincode.net/forums/topic/62891-what-is-fflush/

http://athena.nitc.ac.in/labs/os/html/nettest_8cc.html