mirror of
https://github.com/intel/linux-sgx
synced 2026-06-08 14:49:32 +00:00
Li, Xun
d10cabebb5
Added new APIs in sgx_uae_service.h and sgx_ukey_exchange.h to support ECDSA quote based remote attestation. The set of legacy APIs supports EPID only and the set of new APIs supports ECDSA quotes. Enhanced Edger8r with structure deep-copy feature. Fixed bugs. Signed-off-by: Li, Xun <xun.li@intel.com>
81 lines
3.2 KiB
ReStructuredText
81 lines
3.2 KiB
ReStructuredText
.. _concept-resources:
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The Resource System
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===================
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The C++ Micro Services library provides a generic resource system that allows you to:
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- Embed resources in a bundle.
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- Access resources at runtime.
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The features and limitations of the resource system are described in more detail in
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the following sections.
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Embedding Resources in a Bundle
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-------------------------------
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Resources are embedded into a bundle's shared or static library (or into
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an executable) by using the :program:`usResourceCompiler3` executable. It will
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create a ZIP archive of all input files and can append it to the bundle
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file with a configurable compression level. See :any:`usResourceCompiler3(1)`
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for the command line reference.
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Accessing Resources at Runtime
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------------------------------
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Each bundle provides individual resource lookup and access to its embedded
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resources via the :any:`Bundle <cppmicroservices::Bundle>` class which provides methods
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returning :any:`BundleResource <cppmicroservices::BundleResource>`
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objects. The BundleResource class provides a high-level API for accessing
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resource information and traversing the resource tree.
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The :any:`BundleResourceStream <cppmicroservices::BundleResourceStream>`
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class provides a ``std::istream`` compatible object for the seamless usage of
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embedded resource data in third-party libraries.
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Resources are managed in a tree hierarchy, modeling the original parent-child
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relationship on the file-system.
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The following example shows how to retrieve a resource from each
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currently installed bundle whose path is specified by a bundle property:
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.. literalinclude:: snippets/uServices-resources/main.cpp
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:language: cpp
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:start-after: [2]
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:end-before: [2]
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This example could be enhanced to dynamically react to bundles being
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started and stopped, making use of the popular *extender pattern* from
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OSGi.
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Runtime Overhead
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----------------
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The resource system has the following runtime characteristics:
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- During bundle install, the bundle's ZIP archive header data (if available)
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is parsed and stored in memory.
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- Querying ``Bundle`` or ``BundleResource`` objects for resource
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information will not extract the embedded resource data and hence
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only has minimal runtime and memory overhead.
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- Creating a ``BundleResourceStream`` object will allocate memory for
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the uncompressed resource data and inflate it. The memory will be
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free'ed after the ``BundleResourceStream`` object is destroyed.
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Conventions and Limitations
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---------------------------
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- Resources have a size limitation of 2GB due to the use of the ZIP format.
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- Resource entries are stored with case-insensitive names. On
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case-sensitive file systems, adding resources with the same name but
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different capitalization will lead to an error.
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- Looking up resources by name at runtime *is* case sensitive.
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- The CppMicroServices library will search for a valid zip file inside
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a shared library, starting from the end of the file. If other zip
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files are embedded in the bundle as well (e.g. as an additional
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resource embedded via the Windows RC compiler or using other
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techniques), it will stop at the first valid zip file and use it as
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the resource container.
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