Model Package Support (Phase 2)

[chilo-ms]

This pull request introduces a new public C API for loading, inspecting, and creating sessions from ONNX Runtime model packages.

Following are the new C APIs:

namespace OrtModelPackageAPI {

ORT_API(const OrtModelPackageApi*, GetModelPackageApi);

ORT_API(void, ReleaseModelPackageOptions, _Frees_ptr_opt_ OrtModelPackageOptions*);
ORT_API_STATUS_IMPL(CreateModelPackageOptionsFromSessionOptions,
                    _In_ const OrtEnv* env,
                    _In_ const OrtSessionOptions* session_options,
                    _Outptr_ OrtModelPackageOptions** out);

ORT_API(void, ReleaseModelPackageContext, _Frees_ptr_opt_ OrtModelPackageContext*);
ORT_API_STATUS_IMPL(CreateModelPackageContext,
                    _In_ const OrtEnv* env,
                    _In_ const ORTCHAR_T* package_root,
                    _In_ const OrtModelPackageOptions* options,
                    _Outptr_ OrtModelPackageContext** out);

ORT_API_STATUS_IMPL(ModelPackageContext_GetComponentModelCount,
                    _In_ const OrtModelPackageContext* ctx,
                    _Out_ size_t* out_count);
ORT_API_STATUS_IMPL(ModelPackageContext_GetComponentModelName,
                    _In_ const OrtModelPackageContext* ctx,
                    _In_ size_t component_index,
                    _Outptr_ const char** out_name);
ORT_API_STATUS_IMPL(ModelPackageContext_GetSelectedVariantFileCount,
                    _In_ const OrtModelPackageContext* ctx,
                    _In_ const char* component_name,
                    _Out_ size_t* out_count);
ORT_API_STATUS_IMPL(ModelPackageContext_GetSelectedVariantFileIdentifier,
                    _In_ const OrtModelPackageContext* ctx,
                    _In_ const char* component_name,
                    _In_ size_t index,
                    _Outptr_ const char** out_file_identifier);

ORT_API_STATUS_IMPL(ModelPackageGetFileSessionOptions,
                    _In_ const OrtModelPackageContext* context,
                    _In_ const char* component_name,
                    _In_opt_ const char* file_identifier,
                    _Outptr_result_buffer_maybenull_(*num_entries) const char* const** option_keys,
                    _Outptr_result_buffer_maybenull_(*num_entries) const char* const** option_values,
                    _Out_ size_t* num_entries);

ORT_API_STATUS_IMPL(ModelPackageGetFileProviderOptions,
                    _In_ const OrtModelPackageContext* context,
                    _In_ const char* component_name,
                    _In_opt_ const char* file_identifier,
                    _Outptr_result_buffer_maybenull_(*num_entries) const char* const** option_keys,
                    _Outptr_result_buffer_maybenull_(*num_entries) const char* const** option_values,
                    _Out_ size_t* num_entries);

ORT_API_STATUS_IMPL(CreateSession,
                    _In_ const OrtEnv* env,
                    _In_ OrtModelPackageContext* ctx,
                    _In_ const char* component_name,
                    _In_opt_ const char* file_identifier,
                    _In_opt_ const OrtSessionOptions* session_options,
                    _Outptr_ OrtSession** session);

}

Please see the variant metadata schema:
https://github.com/microsoft/onnxruntime/blob/jambayk/model-package/docs/design_docs/model_package_api.md#variant-metadata-schema

The most important changes are:

Public C API Additions

• Introduced new API types and functions for model package support, including OrtModelPackageApi, OrtModelPackageOptions, and OrtModelPackageContext, along with a new GetModelPackageApi() method on the main OrtApi struct. These allow clients to enumerate models in a package, query variant metadata, and create sessions for specific package components. [1] [2] [3] [4]

Documentation

• Added a detailed API usage example and design rationale to model_package/README.md, outlining the typical workflow for using the new model package APIs and describing session/variant selection precedence.

Internal Data Structure Refactoring

• Refactored model package and variant metadata structures to support multiple files per variant, richer compatibility metadata, and per-file session/provider options. Introduced new types: VariantEpCompatibilityInfo, VariantModelInfo, ModelVariantInfo, ComponentModelInfo, and ModelPackageInfo.
• Updated the ModelPackageContext class to provide query APIs for enumerating component models, variants, and file-level metadata, as well as for resolving file paths and retrieving session/provider options for selected variants.

Manifest Parsing

• Updated the manifest/metadata parser to handle the new schema, supporting multiple models per variant and richer compatibility constraints.

These changes collectively provide a robust foundation for supporting ONNX model packages in the ONNX Runtime C API, enabling advanced workflows such as variant selection based on execution provider compatibility and custom session/provider options.### Description

Motivation and Context