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📝 Netlink Attributes: An Overview 🚀

📌 Introduction:

🔍 Background:

  • So far, we've set up basic Netlink socket-based communication between user space and kernel space.
  • The Netlink protocol demands the use of the TLV (Type-Length-Value) format for data exchange.

🎯 Structure of Netlink Data:

  • The Netlink message starts with the Netlink message header.
  • Following the header, there's a payload, which should be in the form of discrete TLVs.
  • Example: A payload formatted in four TLVs.

📌 TLV in the Context of Netlink:

🔍 Basic Anatomy:

  • Each TLV can have a variable size.
  • Three components: Type, Length, and Value.
  • For Netlink, the Type and Length fields occupy two bytes each (instead of the typical one byte).

🎯 Netlink Attribute Data Structure:

  • Netlink APIs offer a structure called Netlink attribute for defining the Netlink type and length.
  • Each of these (type and length) is 16 bits or two bytes.
  • The Value part can vary in size.
  • Example: TLV with length of 32 bytes, type code 2, and its value. Another TLV with length of 64 bytes, type code 3, and its value.

🔎 Interpretation of TLVs:

  • The recipient (either user space or kernel space) must know how to interpret TLV codes.
  • If the recipient doesn't recognize a TLV code, they should skip it.
  • The standardized format: A Netlink message header followed by a payload formatted in TLVs.

📌 Interaction with Linux Kernel:

🔍 Linux Kernel APIs:

  • Linux provides macros for working with Netlink headers and TLVs.
  • Detailed exploration of these macros will be in the programming section.

🎯 Cascading Netlink Messages:

  • A unique feature of Netlink messages: they can be cascaded.
  • A new Netlink message header can be appended right after the payload of the first Netlink message header.
  • These cascaded messages can be exchanged in any direction between user space and kernel space.

🤔 Interview Questions about Netlink Attributes:

  1. Question: What is the role of the Netlink protocol in kernel-user space communication?

    Answer: The Netlink protocol facilitates socket-based communication between user space and kernel space, allowing for the exchange of data in the TLV (Type-Length-Value) format.

  2. Question: How are TLVs structured in the context of the Netlink protocol?

    Answer: In Netlink, each TLV has the Type and Length fields occupying two bytes each, followed by a variable-sized Value field.

  3. Question: What action should be taken if a recipient encounters an unrecognized TLV code?

    Answer: If the recipient does not recognize a TLV code, they should simply skip it, ensuring robustness in communication.

  4. Question: Describe the concept of cascading in the context of Netlink messages.

    Answer: Cascading in Netlink messages refers to the ability to append a new Netlink message header right after the payload of a preceding message. This feature allows for a sequence of messages to be communicated seamlessly.

I hope this helps with your preparation! 🌟📘