Adding a cache to your mdadm system has significantly improved its latency and reduced the load on the JBOD. Before you finish your internship, however, the company wants you to add networking support to your mdadm implementation to increase the flexibility of their system. The JBOD systems purchased by the company can accept JBOD operations over a network using a proprietary networking protocol. Specifically, a JBOD system has an embedded server component that can be configured to have an IP address and listen for JBOD operations on a specific port. In this final step of your assignment, you are going to implement a client component of this protocol that will connect to the JBOD server and execute JBOD operations over the network. As the company scales, they plan to add multiple JBOD systems to their data center. Having networking support in mdadm will allow the company to avoid downtime in case a JBOD system malfunctions, by switching to another JBOD system on the fly.

Currently, your mdadm code has multiple calls to jbod_operation, which issue JBOD commands to a locally attached JBOD system. In your new implementation, you will replace all calls to jbod_operation with jbod_client_operation, which will send JBOD commands over a network to a JBOD server that can be anywhere on the Internet (but will most probably be in the data center of the company). You will also implement several support functions that will take care of connecting/disconnecting to/from the JBOD server.

Protocol

The protocol defined by the JBOD vendor has two messages. The JBOD request message is sent from your client program to the JBOD server and contains an opcode and a buffer when needed. The JBOD response message is sent from the JBOD server to your client program and contains an opcode and a buffer when needed. Both messages use the same format:

Table 1: JBOD procotol packet format

Implementation

In addition to replacing all calls in mdadm.c, you will implement functions defined in net.h in the provided net.c file. Specifically, you will implement jbod_connect function, which will connect to JBOD SERVER at port JBOD PORT, both defined in net.h, and jbod_disconnect function, which will close the connection to the JBOD server. Both of these functions will be called by the tester. The file net.c contains some functions with empty bodies that can help with structuring your code, but you dont have to implement them. Other than implementing the functions in net.h, it is up to you how you structure your code.

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Testing

Once you finish implementing your code, you can test it by running the provided jbod_server in one terminal, which implements the server component of the protocol, and running the tester with the workload file in another terminal. Below is a sample session from the server and the client:

Output from the jbod_server terminal:

$ ./jbod_server

JBOD server listening on port 3333

new client connection from 127.0.0.1 port 32402 client closed connection

Output from the tester terminal:

$ ./tester -w traces/simple-input >my-out connected to the JBOD server at 127.0.0.1

Cost: 0 Hit rate: -nan%

closed connection to the JBOD server

You can also run the jbod_server in verbose mode to print out every command that it receives from the client. Below is sample output that was trimmed to fit the space.

$ ./jbod_server -v

JBOD server listening on port 3333

new client connection from 127.0.0.1 port 38546 received cmd id = 0 (JBOD_MOUNT) [disk id = 0 block id = 0], result = 0 received cmd id = 2 (JBOD_SEEK_TO_DISK) [disk id = 0 block id = 0], result = 0 received cmd id = 5 (JBOD_WRITE_BLOCK) [disk id = 0 block id = 0], result = 0 block contents:

0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 Grading

There are not tests for this implementation. All of your 10 points will come from traces.

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