7_UserspaceProgramThreadModel.md

📝 Netlink Userspace Program Development 🚀

1. Introduction: 🌐

In this part of the course, the focus is on creating a Netlink userspace program.

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2. Steps in the Userspace Program: 👩‍💻

1. Creating a Netlink Userspace Socket:

   • The foremost step is to generate a socket specifically for the userspace.

2. Establishing a Separate Thread for Netlink Message Reception:

   • Within the main thread, initiate a secondary thread dubbed the netlink message receiver thread.

   • This thread solely dedicates itself to accept incoming messages from kernel space.

     graph TD;
       A[Main Thread (Yellow)] -->|Create| B[Receiver Thread (Blue)];
       A -->|Send Messages| C[Kernel Space];
       B -->|Receive Messages| C[Kernel Space];
     

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3. Main Thread Responsibilities:

   • Acts as a conveyor, transmitting messages to the kernel space.
   • Can be envisioned as a menu-driven program:
     • Presents users with multiple choices for dispatching varied data types to the kernel space.
     • Asks users to input a greeting message for the kernel.
     • Sends user's chosen message to the kernel space receiver thread.

4. Receiver Thread Responsibilities:

   • Exclusively tasked with acknowledging messages from kernel space.
   • In our scenario, the thread awaits a greet reply.

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3. Summarized Design: 🎨

The userspace application's architecture is straightforward:

• It's a dual-threaded application.
• One thread (main thread) handles sending messages to the kernel space.
• The other (receiver thread) manages the receipt of messages from the kernel space.

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🤓 Interview Questions: 📜

1. Q: What is the initial step in creating a Netlink userspace program?

   A: The first step is to create a Netlink socket specifically for the userspace.

2. Q: Why do we introduce a separate thread (receiver thread) in the userspace program?

   A: The separate receiver thread is established to solely receive messages from the kernel space, ensuring that message sending and receiving functionalities are isolated and can operate simultaneously.

3. Q: How can you differentiate between the main thread and the receiver thread in terms of responsibilities in the userspace program?

   A: The main thread is responsible for sending messages to the kernel space, often based on user input or choices. In contrast, the receiver thread exclusively handles the receipt of messages from the kernel space.

4. Q: In the described userspace program, what kind of reply does the receiver thread anticipate from the kernel?

   A: The receiver thread anticipates a greet reply from the kernel space.

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📘 Resources:

1. Netlink Socket Overview
2. Multi-threading in C

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