R. Levin, E.S. Cohen, W.M. Corwin, F.J. Pollack, and W.A. Wulf. Policy /mechanism separation in HYDRA. In ACM Symposium on OS Principles, pages 132--40, 1975.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....is of paramount importance. Anticipating that processor scheduling based on traditional timesharing would not be suitable for the support of multimedia applications, attempts have been made to adapt static real time schemes to support the timeliness requirements of multimedia applications [6][11] 13] Not only do they rely on static predictability and forced low resource utilization, but they require painful hand tuning by the user to allow conventional interactive and batch activities to run. These ailments make such schemes unacceptable for the highly dynamic multimedia ....

....unacceptable for the highly dynamic multimedia environment. Because of the difficulty of scheduling conventional interactive and batch activities together with real time continuous media activities, proposed solutions with actual implementations have predominantly been two level schedulers [6]. These schedulers support separate scheduling policies for conventional tasks and real time tasks on top of a base level scheduling mechanism [1] 3] 4] No matter how sophisticated the policies may be, the scheduler s overall effectiveness is limited by a typically static base level mechanism ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, W. Wulf: Policy/ Mechanism Separation in Hydra, Proceedings Fifth Symposium on Operating Systems Principles, ACM, November, 1975.

....bureaucratic inertia, has led numerous organizations to use Unix based gateways. The mechanisms described in this paper allow users of Unix based gateways to impose packet level access controls without major changes to existing software. Perhaps more important, by separating mechanism from policy [17] so that arbitrarily precise access control policies may be developed as ordinary Unix user processes, these mechanisms support fine tuning and experimentation that would be difficult using commercial gateway products. Section 2 of this paper sets out the background and goals of this project, and ....

....quite frequently) In other words, it pays to separate the mechanism for forwarding packets from the policy that decides what should be forwarded. Although the underlying concept has been known for a long time, the term policy mechanism separation was invented by the designers of the Hydra system [17], who established it as a basic design principle . of a kernel composed (almost) entirely of mechanisms. Policies were embodied in user level processes, thus improving flexibility while keeping the kernel simpler and presumably more reliable. The Unix kernel, on the other hand, contains most ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in Hydra. In Proc. 5th Symposium on Operating Systems Principles, pages 132-140. ACM, November, 1975.

....a single operating system mechanism capable of supporting a wide range of security policies is not a new goal. The Hydra operating system developed in the 1970 s introduced a security model explicitly based upon the separation of access control mechanisms from the definition of a security policy [30, 53]. Hydra was a capability based system, though the developers of the system recognized the limitations of a simple capability model and introduced several enhancements to the basic capability mechanisms in order to satisfy a specific collection of security policies. The result was that while Hydra ....

R. Levin, E. Cohen, W. Corwin, P. F., and W. Wulf. Policy /mechanism separation in Hydra. In Proceedings of the Fifth Symposium on Operating Systems Principles, pages 132--140, Unversity of Texas at Austin, Nov. 1975. ACM/SIGOPS.

....3.1 Capability Based Systems The goal of a single operating system mechanism capable of supporting a wide range of security policies is not a new goal. The Hydra operating system developed in the 1970 s separated its access control mechanisms from the definition of its security policy [29, 52]. Hydra was a capability based system, although the developers of the system recognized the limitations of a simple capability model and introduced several enhancements to the basic capability mechanisms. The Hydra approach was taken even further by the KeyKOS [40] and EROS [47] systems. Though ....

R. Levin, E. Cohen, W. Corwin, P. F., and W. Wulf. Policy /mechanism separation in Hydra. In Proceedings of the Fifth Symposium on Operating Systems Principles, pages 132--140, Unversity of Texas at Austin, Nov. 1975. ACM/SIGOPS.

.... Context Context Context a meta link between the Context structures an association link between an object and its Context structure metaspace of these objects metaspace of this object metaspace of reflectors Figure 4: The MetaCore Implementation In retrospect, we can review similar mechanisms in [Levin et al. 75] and recently in [Anderson et al. 91] and [Marsh et al. 91] in the sense that a kernel does not handle scheduling policies. MetaCore provides the public primitives shown in Table 5. We can use these primitives using a C interface as shown in Figure 5. The interface is so designed as to be ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. POLICY/MECHANISM SEPARATION IN HYDRA. In Proceedings of the 5th ACM Symposium on Operating System Principles, pp. 132--140. ACM Press, November 1975.

....One solution to this problem is to allow applications to specify their own policies, in the form of specialized operating system components. In general, this approach requires that interfaces, previously hidden within the kernel, be defined and exposed to application developers. Hydra [16] was an early example of a customizable operating system. The goal of the Hydra kernel was to implement mechanisms, while allowing application level software to define policies. The invocation of application level software on each policy decision was deemed to be impractical due to the high cost ....

R Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/Mechanism Separation in Hydra. In Proceedings of the 5th Symposium on Operating System Principles (SOSP'75), pages 132--140, November 1975.

....application specific policies. Most of the hardware dependencies are limited to a well defined set of modules, to ease the portability of the kernel. The origins of many of the current trends in the modern operating system designs can be traced to the RC4000 [Hansen 1970] nucleus and the Hydra [Levin et al. 1975] design. The RC4000 nucleus design clearly states, as one of its goals, the need to support different operating system implementations above the facilities of the nucleus. Hydra adopted the object model of computing and also elaborated design goals for kernel mechanisms to implement operating ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy /Mechanism Separation in Hydra. Proceedings of the Fifth Symposium on Operating Systems Principles, pages 132--140, November 1975.

....micro kernel structuring, object based structuring, open system structuring, and virtual machine structuring. Detailed discussions of these methods are given in [Yokote et al. 91b] Object metaobject separation can subsume these structuring methods. In contrast to policy mechanism separation [Levin et al. 75] for example, we can implement an object as a policy module, and a metaobject as a mechanism module. However, this correspondence of object metaobject separation to policy mechanism separation does not correctly express the difference. That is, in the sense that a metaobject represents an ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. POLICY /MECHANISM SEPARATION IN HYDRA. In Proceedings of the 5th ACM Symposium on Operating System Principles, pp. 132--140. ACM Press, November 1975.

....applications can perform effectively. 6. 4 Two level Scheduling Because creating a single scheduler to service both real time and conventional resource requirements has proven difficult, a number of hybrid schemes [1] 4] 6] have been proposed based on the traditional two level scheduler approach [13]. These approaches attempt to avoid the problem by having statically separate schedulers for realtime and conventional applications, respectively. However, all of the mechanisms that have been used for combining these scheduling policies ignore real time requirements. In the best case, these ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, W. Wulf: Policy/Mechanism Separation in Hydra, Proceedings of the Fifth Symposium on Operating Systems Principles, ACM, November 1975.

....at Purdue University) Mach RP3 (developed at T. J. Watson Research Center, IBM) and a few successful commercial systems like Dynix (developed for Sequent Multiprocessors) Chrysalis (developed for BBN Butterfly machines) UMAX (developed for Encore Multimax multiprocessors) 4. 1 HYDRA HYDRA [258, 256, 257, 259, 142, 58] is one of the earliest successful multiprocessor kernels, developed at Carnegie Mellon University and implemented on the C.mmp hardware. Extensive descriptions of the HYDRA system appear in [120] and [258] The major goals of HYDRA are: 1. to develop a minimal kernel for multiprocessor systems ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in hydra. In Proceedings of the 5th Symposium on Operating System Principles, Austin, Texas, Nov. 1975.

....programmability, extensibility, and scalability of high performance applications. A variety of research results has enabled the runtime configuration of operating systems in order to improve the performance of specific user programs, including the early work on policymechanism separation in Hydra[41, 12], the removal of operating system services from fixed kernels to the configurable user level in the Mach[53] and NT[13] operating systems, and ultimately leading to the notion of micro kernels and user level libraries for implementing customized operating system abstractions[8, 19] In effect, ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in hydra. In Proc. of the 5th ACM Symposium on Operating System Principles, Nov. 1975.

.... the difficulty of scheduling conventional interactive and batch activities together with real time continuous media activities, proposed solutions with actual implementations have predominantly been static two level schemes [1] 3] 5] By allowing multiple policies on top of a base level mechanism [7], they attempt to avoid the integration problem by supporting separate conventional and real time scheduling policies. Their drawback is that no matter how sophisticated the layered scheduling policies or how general the base level mechanism may be [13] scheduling among computations in different ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, W. Wulf: Policy/Mechanism Separation in Hydra, Proceedings Fifth Symposium on Operating Systems Principles, ACM, November, 1975.

....on a myriad of user preference rules is a very difficult problem, and the difficulty is exacerbated by the fact that the direct approach does not incorporate any structure to help organize the problem. We believe that we can fruitfully apply the principle of separation of policy and mechanism [10] to the problem of managing operating system resources to ensure quality of service (QOS) requirements for distributed applications. We separate the mechanism for controlling resource consumption from the policy that determines how the resource capacity should be allocated, and we are left with ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/Mechanism Separation in HYDRA. In Proceedings of the 5th ACM Symposium on Operating Systems Principles, pages 132--140, 1975.

....retransmission timeout algorithm, and the algorithm for selecting alternative name servers. When DNS was initially deployed, these mechanisms were intentionally left unspecified because good solutions were not yet known. Perhaps this was done to separate the specification of mechanism and policy [4]. Today, nine years after DNS s initial deployment, reasonable solutions for each of these issues are known; this section presents one such solution. 2.1 Caching DNS name servers cache responses to their successful queries. Usually, they do not cache responses indicating that a name is bad or ....

Roy Levin et al. Policy/mechanism separation in HYDRA. Proc. 5th Symp. on Operating Systems Principles, 1975.

.... at the loss of ease of programming[11, 29] However, in the recent past, operating system researchers have addressed the issue of matching operating system to application functionality and performance (1) by offering users the ability to write custom policies on minimal, low level mechanisms[14, 7] or to tailor their programs to different target operating systems or hardware configurations[25] 2) by removing operating system services from kernel to user levels, ultimately leading to current notions of micro kernels, and (3) by designing new interfaces between the operating system and ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in hydra. In Proceedings of the 5th ACM Symposium on Operating System Principles, Nov. 1975.

....We believe that the drawbacks to these facilities are outweighed by their benefits for performancecritical parallel programming. This view of what a programming environment should do is consistent with accepted systems design goals of separating policy from mechanism and not hiding power [Levin et al. 75, Lampson 84] The underlying assumption is that the needs of different applications vary so much that a more restricted model cannot possibly perform well in all situations. We believe that programmers are willing to devote careful thought and effort to achieving the best performance, but that ....

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in hydra. In Proceedings of the Fifth ACM Symposium on Operating Systems Principles, pages 132--140, November 1975.

No context found.

R. Levin, E.S. Cohen, W.M. Corwin, F.J. Pollack, and W.A. Wulf. Policy /mechanism separation in HYDRA. In ACM Symposium on OS Principles, pages 132--40, 1975.

No context found.

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in Hydra. In 5th ACM Symposium on Operating Systems Principles, pages 132--140, 1975.

No context found.

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/Mechanism Separation in Hydra. In Proceedings of the Fifth ACM Symposium on Operating Systems Principles, pages 132--140, Austin, Texas, October 1975.

No context found.

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in hydra. In Proceedings of the 5th Symposium on Operating System Principles, Austin, Texas. Assoc. Comput. Mach., SigOps, Nov. 1975.

No context found.

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy /mechanism separation in hydra. In Proc. of the 5th ACM Symposium on Operating System Principles, Nov. 1975.

No context found.

Levin, R., E. S. Cohen, W. M. Corwin, F. J. Pollack, and W. A. Wulf (1975). Policy/Mechanism Separation in Hydra. Proceedings of the Fifth ACM Symposium on Operating System Principles, pp. 132-140.

No context found.

R. Levin, E. Cohen, W. Corwin, F. Pollack, and W. Wulf. Policy/mechanism separation in Hydra. In Proceedings of the Fifth ACM Symposium on Operating System Principles (SOSP), pages 132--140, November 1975.

No context found.

Roy Levin, Ellis Cohen, William Corwin, Fred Pollack, and William A. Wulf. Policy /Mechanism Separation in Hydra. In Proceedings of the Fifth Symposium on Operating Systems Principles, pages 132-- 140, Austin, TX, November 1975.

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC