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Common Management Programming Interface (CMPI) Providers in a nutshell
============================

Aug 1st, 2005

Pegasus 2.5 *NEWS*
------------------

The CMPI macro header files (cmpimacs.h) shipped is OpenPegasus specific. This 
will change once OpenGroup releases a specification with the macro definitions.

The CMPI Function Table (cmpift.h) file and CMPI Data Types (cmpidt.h) file are
 composed from the CMPI v1.0 specification + Technical Corrigenda and are
binary compatible with the "historical implementations" and the 1.0 specification
augmented with the Technical Corrigenda.


Build CMPI from sources
-----------------------

The Common Manageability Programming Interface (CMPI) has been integrated into
Pegasus as a pluggable provider manager.

CMPI is by default enabled on Linux. For other platforms it must be enabled 
during Pegasus build.

For CMPI enablement, set the following environment variables prior to make:

   PEGASUS_ENABLE_CMPI_PROVIDER_MANAGER=1


Using CMPI
----------
If you plan to write your own CMPI providers you are kindly referred to the
WBEMSource homepage where the draft specification document for CMPI resides.
You can find at http://www.wbemsource.org/doc.tpl?CALLER=index.tpl&gdid=3712 .
If you are looking for samples you should have a look at the SBLIM project.
The packages prefixed by the string sblim-cmpi contain CMPI providers for
various classes. See http://www-124.ibm.com/developerworks/projects/sblim .

Using CMPI with threads
-----------------------

CMPI provides API functions for low-level thread, mutex and conditional constructs.
Hence you can compile your provider without needing to link to pthread or other 
threading library. 

However, the developer is responsible for memory management of these constructs and
as well of exiting the threads before the cleanup function is exited. If this is not 
done, the thread will be forcefully terminated. This can have the nasty consequence of
hanging CIMServer, or bringing down the CIMServer, or just the Out-of-Process Provider 
Agent if you run OpenPegasus with 'run-as-requester' configuration flag turned on.
Please refer to the Admin Guide or the readme files for more details about this flag.

Using CQL with CMPI
-------------------

 To use CQL support for indications and exec query you will have to use
 the Pegasus/Provider/CMPI/cmpi_cql.h header file with one new function.
 You also  you need to define PEGASUS_USE_EXPERIMENTAL in your 
 code to take advantage of these CQL utility functions. The reason is that 
 the CMPI standard 1.0 is unclear on one thing:
 
   - CMNewSelectExp. One of arguments passed is a 'projection' array. The
     spec does not explain exactly what in such array. Implementation of
     CMPI that also implemented WQL put a string representation of the 
     properties, as "SystemName", "Hostname", etc. But that is not neccesarily
     the case with CQL, where you can have chained identifiers such as
     "CIM_OperatingSystem::SystemName". In other words, the CMPI standard
     needs to clarify this and to make the existing providers backward 
     supported, this utility function - CMPI_CQL_NewSelectExp is provided
     until the CMPI standard comes up with a conclusion on this.

  When the CMPI provides a resolution on these issues, this utility
  interface will be gone and unsupported.

  Questions and Answers:
Q1: Is the CMPI Specification really ambiguous or does it 
just not support CQL? If it's ambiguous should it be fixed 
before it goes final?

A1:. Page 96 of the CMPI review spec states (line 2899-2901): The *projection output argument is 
a pointer to a CMPIArray structure of CMPIString entries containing projection specification. 
It shall be set to NULL if no projection is defined.. To clarify any ambigiuity, an e-mail to the
 CMPI review group was sent, which would add the following: The projection specification is query 
language specific. Hence the entries format of the projection output array CMPIString might be 
different depending on the query language. Be sure to check the lang argument for the query language your 
provider will support. . To guard the provider from DMTF's CQL possible ways it can be represented in 
a string format, and since the CQL is experimental, the CMNewSelectExp will NOT support CQL. 
The CMPI_CQL_NewSelect will support both CQL and WQL.


AQ:What happens if an existing Provider is passed a CQL 
statement and issues a newSelectExp call?  Does it return 
an error?

A2: The error code CMPI_RC_ERR_QUERY_LANGUAGE_NOT_SUPPORTED would be set.


Q3: Both CMNewSelectExp and CMPI_CQL_NewSelectExp return a 
CMPISelectExp. Is there anyway to determine whether the 
CMPISelectExp represents a CQL or WQL expression?

A3:Not from the scope of the CMPISelectExp structure. Please note that the routine
 that would exercise the CMPISelectExp has a char *lang passed in as argument. 
This char *lang* can be used to easily determine what query language is used.



Registering CMPI providers with Pegasus
---------------------------------------

Once you have a CMPI provider library you want to register it with Pegasus.
How? Well it's almost the same as for C++ providers. The only difference is
that the Provider.Interface property must be set to "CMPI".

Here's an excerpt from the SBLIM Linux Computer System provider registration

// ===================================================================
// 	Linux_ComputerSystem
// ===================================================================


instance of PG_ProviderModule
{
   Name = "OSBase_ComputerSystemProviderModule";
   //The library name on disk
   Location = "cmpiOSBase_ComputerSystemProvider";
   Vendor = "SBLIM";
   Version = "1.2.2";
   InterfaceType = "CMPI";
   InterfaceVersion = "0.86.0";
};

instance of PG_Provider
{
   //The provider module as defined in PG_ProviderModule
   ProviderModuleName = "OSBase_ComputerSystemProviderModule";
   // The provider name as referenced in the code
   Name = "OSBase_ComputerSystemProvider";
};

instance of PG_ProviderCapabilities
{
   //The provider module as defined in PG_ProviderModule
   ProviderModuleName = "OSBase_ComputerSystemProviderModule";
   //The provider name as defined in PG_Provider
   ProviderName = "OSBase_ComputerSystemProvider";
   CapabilityID = "1";
   //Name of the CIM class as defined in the mof
   ClassName = "Linux_ComputerSystem";
   Namespaces = {"root/cimv2"};
   ProviderType = { 2,5 }; // Instance, Method
   SupportedProperties = NULL; // All properties
   SupportedMethods = NULL; // All methods
};