Switch Abstraction Interface (SAI)

SAI PTF is an auto-generated, Python-based dataplane testing framework. It uses Thrift wrapper functions to call C-based SAI functions from Python scripts. The framework's primary goal is to automate the creation of wrapper functions by generating them directly from SAI headers, reducing manual effort when testing new SAI versions.

Key components include:

• Autogeneration framework: Uses existing SAI meta infrastructure to generate code.
• PTF tests: Functional tests for L2, L3, tunnels, and mirroring.
• DASH support: Optimized tests for platforms with limited port counts.

The SAI for OTN extension provides technical specifications for managing optical components on Optical Transport Network (OTN) devices within the SONiC ecosystem. It allows for end-to-end management across both packet and optical layers (L0–L4).

Core functions provided by the OTN SAI include:

• Creation and removal of OTN components.
• Retrieval of current operational status of OTN components.
• Notification handling for failures and hardware data reporting.
• Execution of hardware-specific operations (e.g., optical path switching, triggering optical measurements).

All OTN objects are subobjects of the switch root element and are designed to be isolated from existing non-OTN SAI objects to prevent impact on packet switch functionality.

gensairpc.pl is a tool that scans SAI headers to generate RPC components. The workflow consists of two main phases:

1. Parsing:
   • Generates Doxygen XML files from SAI headers using SAI/meta tools.
   • Uses SAI/meta utilities to extract data.
   • Creates Perl objects representing SAI code elements (Attributes, Enums, Functions, Statistics, Structures, Typedefs, Types, and Variables).
2. Generation:
   • Generates sai.thrift using Template Toolkit (TT).
   • Uses Thrift to generate sai_rpc_server.skeleton.cpp.
   • Converts the skeleton into a sai_rpc_server.cpp.tt template.
   • Generates sai_rpc_server.cpp and sai_adapter.py using Template Toolkit.

Finally, the tool performs optional formatting and cleanup.

Prefix Compression is a feature that enables mapping an IP prefix/mask (the longest prefix) to a specific meta-data value. These mappings are stored in a SAI_OBJECT_TYPE_PREFIX_COMPRESSION_TABLE.

Key capabilities include:

• Creating tables that support both IPv4 and IPv6 entries.
• Grouping prefixes to enhance features like ACLs by matching against the associated meta-data.
• Configuring tables for specific stages (Ingress/Egress) and types (Source addresses, Destination addresses, or both).

The Switch Abstraction Interface (SAI) is a vendor-independent API designed to provide a uniform way of controlling network forwarding elements, such as switching ASICs, NPUs, or software switches. It allows the Control stack (the software managing the network) to be written independently of the underlying hardware (the Forwarding Element).

Key characteristics include:

• OS-agnostic: Designed to work across different operating systems (e.g., *nix, Windows).
• Attribute-based: Uses attributes to minimize compatibility issues with structure versioning and to allow for API extensibility.
• CRUD-based: Uses Create, Read, Update, and Delete operations to manage SAI objects.
• Managed API: Supports versioning to maintain backward compatibility. If a function's signature or semantics change, a new function with a unique versioned ID (e.g., SAI_API_VLAN2) is created.

The SAI IPsec API provides a software interface for IPsec ESP tunnel mode (RFC-4303) and UDP-encapsulated IPsec ESP tunnel mode (RFC-3948). It specifically supports the GCM-AES ciphersuite.

Key responsibilities include:

• Egress Transformation (Tunnel Origination): Switching a packet to an IP tunnel, adding tunnel headers (IP and optionally UDP-ESP), and applying egress packet security (adding ESP header/trailer, ICV, and optional encryption).
• Ingress Transformation (Tunnel Termination): Decrypting payload, verifying integrity/authenticity, removing ESP headers/trailers/ICV, and removing the tunnel header to switch the inner packet.

Note: Key exchange protocols are outside the scope of this API.

The autogeneration process is written in Perl and uses SAI headers (processed via SAI meta into Doxygen XML) and templates to produce the following files:

All files are generated using the gensairpc.pl script.