1 mike 1.2 //%/////////////////////////////////////////////////////////////////////////////
2 //
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22 mike 1.2 //==============================================================================
23 /*
24 */
25
26 /** @name Pegasus Architecture
27
28 This section defines the overall architecture of the Pegasus implementation.
29
30 */
31 //@{
32 /** @name Design Goals
33
34 The Pegasus design team set some basic design goals early in the development of Pegasus as follows:
35 <UL>
36 <LI>C++ as the core development language. We selected C++ because it represented a compromise between the ability to work with objects and a language that would be acceptable for high avaailablity platforms.
37 <LI>Modular Architecture - We wanted to be able to create the architecture based on well understand standardized modules that have clean well defined interfaces between the modules.
38 <LI>Open to a wide range of specialization and customization.
39 <LI>Minimize the functionality of the basic core CIMOM. We wanted to create an environment where the majority of customization could be created by working with attached modules that would both extend and modify the functionality of the broker.
40 <LI>Use only open source components in the pegasus environment
41 <LI>Design for maximum portability. The initial targets would be Linux, Unix, and NT but the product should be usable in a wide variety of platforms and platform sizes.
42 <LI>The APIs and interfaces should be clear, given that they are in C++
43 mike 1.2 <LI>
44 </UL>
45 */
46
47
48 /** @name The Broker
49
50 The Common Information Model Object Broker (often known as the CIM Information
51 manager or CIMOM) brokers CIM objects between a number of sources and
52 destinations. A CIM object should be a representation, or model, of
53 a managed resource, such as a printer, disk drive, or central processing unit
54 (CPU). In the Pegasus implementation, CIM objects are represented
55 internally as C++ classes. The CIMOM transfers information
56 between WBEM clients, the CIM Object Manager Repository, and managed
57 resources.
58
59 */
60
61 /** @name Pegasus Providers.
62 ATTN: Define in more detail
63
64 mike 1.2 */
65
66 /** @name Extension Services
67 ATTN: Document this as an architectural component
68 */
69
70
71 /** @name Pegasus Clients.
72 ATTN: define in more detail
73
74 */
75
76 /** @name Functional Flow
77
78 The Common Information Model Object Broker (often known as the CIM Information
79 manager or CIMOM) brokers CIM objects between a number of sources and
80 destinations. A CIM object should be a representation, or model, of
81 a managed resource, such as a printer, disk drive, or central processing unit
82 (CPU). In the Pegasus implementation, CIM objects are represented
83 internally as C++ classes. The CIMOM transfers information
84 between WBEM clients, the CIM Object Manager Repository, and managed
85 mike 1.2 resources.
86
87 NOTE: We are very careful in the use of CIM and WBEM. These are terms defined
88 and controled by the DMTF and they have specific meanings both technically and
89 legally. Thus, the objects are CIM objects. However, the client is a WBEM
90 client because it uses the DMTF XML/HTTP specificaitons to transfer
91 information and that specification and CIM form WBEM.
92
93 When a WBEM client application accesses information about a managed
94 resource, the CIM Object Manager contacts either the appropriate provider
95 for the CIM object that represents that managed resource or the CIM Object
96 Manager Repository. Providers are classes that communicate with managed
97 objects to retrieve data. If the requested data is not available from the CIM
98 Object manager Repository, the CIM Object Manager forwards the request to
99 the provider for that managed resource.
100
101 Using the Repository.
102
103 The provider dynamically retrieves the requested information, which is sent back to the requester. The CIM Object Manager Repository only contains static data. Classes that are handled by a provider must have a Provider qualifier that identifies the provider to contact for the class. When the CIM Object Manager receives a request for a class that has a Provider qualifier, it should route the request to the specified provider. If no provider is specified, it should route the request to the CIM Object Manager Repository.
104
105 When a WBEM client connects to a CIM Object Manager, it will get a handle to the CIM Object Manager. The client can then perform WBEM operations.using this reference. At startup, the CIM Object Manager should perform the following functions: Listen for RMI connections on RMI port 5987 and for XML/HTTP connections on HTTP.
106 mike 1.2
107 NOTE: The current version of the CIMOM does not incorporate events. Therefore, this description is written around a CIMOM without events functionality.
108
109 Note - The listener for connections may not be the Object Manager; it could
110 be another entity that is performing the operation for the Object Manager.
111 This could be a servlet in a Web server. Conformant object managers are
112 required to support XML over HTTP - Pegasus is conformant.
113
114 The CIMOM accepts requests called WBEM Operations from the WBEM client. These operations are explicitly defined in the WBEM specification. They represent the operations possible on CIM objects (ex. create/modify/delete class/instance, etc.) During normal operations, the CIMOM performs the following for each operation request received:
115 <UL>
116 <LI>Security checks to authenticate user login and authorization to
117 access the CIMOM information.
118 <LI>Syntactic and semantic checks of the CIM data operations to
119 ensure that they comply with the current version of the CIM
120 specification.
121 <LI>Route requests to the appropriate provider orthe Repository.
122 The CIMOM iteself does not serve as a Repository for CIM class definitions and instance data. Persistence is provided by the Repository; however, the contact point is the CIMOM. Thus, the Repository could be considered as an option except that the CIMIM is required to keep class information for all semantic and syntatic confirmation and therefore the class repository is a requirement of a working CIMOM, not an option.
123 <LI>Deliver data from providers and from the CIM Object Manager
124 Repository to the originating WBEM client application.
125 </UL>
126 The CIMOM should be a process that accepts requests for CIM
127 mike 1.2 operations, as defined by the DMTF, and carries out these operations. The
128 Pegasus CIMOM runs as a daemon process that waits for requests.
129
130 <B>Authentication</B>
131
132 Before any requests can be made to the CIM Object Manager, an
133 authenticated session must be established.
134
135 NOTE:The current version of Pegasus does not
136 have any authentication. However, it is planned for version 1.1.
137
138 An identifier for the user and optionally a role will be associated with the authenticated session. A role is a principal identity associated with the current session, in addition to the user identity. Systems that do not support roles can ignore them as described in the Security Interface. These can be maintained in an internal Hash map.
139
140 <B>Request Reception</B>
141
142 The CIMOM receives requests through CIM operations over HTTP. Each request will be associated with a session that is set up as part of the initial authentication exchange. Since the session has an associated user, each request automatically has a user associated with it. This should be useful for authorization checking for a given request. Once the request has been received, the appropriate components for handling the specific request will be invoked. The Pegasus implementation has methods for each of the major CIM operations over HTTP. Once the request is received, the appropriate method will be called..
143
144 <B>Authorization</B>
145
146 The default implementation is Access Control List (ACL) based. Access
147 control lists can be maintained per namespace or on a per namespace/user
148 mike 1.2 basis. These lists will be maintained in the root/security namespace. The CIM
149 Object Manager will grant read or write permissions within a namespace
150 based on the access control list. Since CIM operations are done within the
151 context of a namespace, these ACLs will enforce rules on whether an
152 operation should be allowed. For operations that will ultimately be handled by
153 a provider, the appropriate provider can replace the authorization scheme.
154 This will allow providers to enforce finer grained control if desired. A
155 provider
156 can replace the default authorization checking scheme by implementing the
157 Authorizable interface. If implemented, no calls are made to the CIM Object
158 Manager.
159
160 <B>Provider</B>
161
162 <B>Provider RegistrationB/B>
163
164 The Pegasus CIMOM enables developers to write providers, which serve dynamic information to the CIMOM (see Providers). Providers register themselves by specifying their location in a Provider qualifier. Providers can be set up on a class, property, or method basis. Providers can have one or more of the different provider types. The DMTF CIM specification allows the Provider qualifier to have an implementation specific interpretation. For Pegasus, the Provider qualifier constitutes the executable name of a provider executable implementing the provider functions for the class.
165
166
167 There are a number of conceptual interfaces that can be implemented by providers:
168 <UL>
169 mike 1.2 <LI>InstanceProvider
170 <LI>MethodProvider
171 <LI>PropertyProvider
172 <LI>AssociatorProvider
173 </UL>
174 .
175 Each conceptual interface provides a subset of the WBEM Operations as follows:
176
177 NOTE: ATTN: Table defining the types vs. operations
178
179 However
180
181 Providers should be loaded "on
182 demand" by the CIMOM. Classes and properties marked by the
183 provider qualifier will be an indication to the object manager that the
184 associated information is dynamic and must be obtained from the providers
185 rather than the repository. When the object manager determines that a
186 specific request needs dynamic data, provider should be
187 loaded and instantiated. Additionally, the "initialize" method of the Provider
188 will be invoked. There should be only a single instance of the provider.
189
190 mike 1.2 ATTN: Review the following: In the reference implementation, the ProviderChecker maintains a hash map of all the providers. This will enable the CIM Object Manager to load a provider only if it has not been loaded previously. There should be no specified time when a provider can be "unloaded", however providers have a "cleanup" method that can be invoked if, and when, this behavior is specified for the object manager.
191
192 The CIM Object Manager will not act as as a provider for
193 classes. However, there are instances where classes must interact with the CIMOM itself. These might include authentication classes, authorization classes, namespace classes, and classes that provide information on the CIMOM iteslf.
194
195 These classes will be handled by providers but these will be specialized providers that have access back to the CIMOM itself. All of this is being defined as part of a services extension interface to PEGASUS. This interface will be discussed in a future version of this document:
196
197 ATTN: add the services interfaces.
198
199
200
201
202 ATTN: Dealing with multiple providers per class.
203
204
205 <B>Request Routing</B>
206
207 One of the main functions of the CIMOM is operation request routing.
208 Depending on the request, the request may need to be authorized and passed to
209 semantic checkers, providers, and the repository.
210
211 mike 1.2 Requests may be for static information such as schema
212 definitions or static instances. In this case, the CIMOM should
213 route the request to the proper repository.
214
215 The more complex routing will involve operations that can traverse multiple
216 classes and their instances. An example of such an operation is association
217 traversal. In order to determine the associated instances of a given input
218 instance, the CIMOM should first determine the associations
219 that the given instance class participates in. It will obtain this from the
220 associations that have been compiled and stored in the repository. Once
221 these associations are determined, the CIM Object Manager should find
222 those instances of the associations in which the given input instance plays a
223 role. These associations may, or may not be, dynamic. Depending on
224 whether the associations are dynamic or not, the CIM Object Manager may
225 route the requests to providers or the repository. Once the results are
226 returned, they should be concatenated together and returned because of the
227 request. The CIM Object Manager will use schema information to determine
228 which providers to contact. As can be seen, a given request can result in
229 multiple sub-requests to the providers or the repository.
230 A similar situation will occur when a deep enumeration is performed on
231 instances of a class.
232 mike 1.2
233 <B>Semantic Checking</B>
234
235 The CIMOM performs semantic checks before classes or
236 instances can be set or createdusing internal class,
237 property, instance, method, and qualifier checkers and the rules ov validation defined by the CIM specification. These verifiers ensure that the CIM rules are enforced. This includes type verification,type conversions, verification of proper key usage, and other checks.,
238
239 */
240 //@}
241
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