Talk:COMP 3000 Essay 1 2010 Question 1

Microkernel

• Moving kernel functionality into processes contained in user space, e.g. file systems, drivers
• Keep basic functionality in kernel to handle sharing of resources
• Separation allows for manageability and security, corruption in one does not necessarily cause failure in system

Virtual Machine

• Partitioning or virtualizing resources among OS virtualization running on top of host OS
• Virtualized OS believe running on full machine on its own

Exokernel

• Microkernel architecture with limited abstractions, ask for resource, get resource not resource abstraction
• Less functionality provided by kernel, security and handling of resource sharing
• Once application receives resource, it can use it as it wishes/in control
• Keep the basic kernel to handle allocating resources and sharing rather than developing straight to the hardware
• multiplex resources securly providing protection to mutualy distrustfull application threw the use of secure binding's
• Goal of the exokernel is to give LibOS maximum freedom with out allowing them to interfere with each other. to do this the exokernel seperates protection from managment in doing this it provide 3 important tasks[1]
  • tracking ownership of resources [1]
  • ensuring protection by guarding all resource usage and binding points (not to shure what binding points are)[1]
  • revoking acces to the resources [1]
• LibrayOS (LibOs)
  • Reduces the numbrt of kernel crossings[1]
  • Not trusted by the exokernel so can be trusted by the application , Example given is a bad pramater passed to the LibOs only the application is affected.[1] (So LibOs cant interact with kernel ???)
  • Any application running on the Exokernel can change the LibrayOs freely [1]
  • Application that use LibOS that implement standard interfaces (POSIX) will be portable on any system with the same interface [1]
  • LibOs can be made portable if it is desgined to interact with a low-level machine independant level to hide hardware details [1]

Exokernel Design

Design Principles

• Securely Expose Hardware [1]
  • an Exokernel tries to creat low level primatives that the hardware resources can be accesse from, this allso includes interrupt's,exceptions [1]
  • the exokernel also export priviledged instructions to the LibOS so that traditional OS abstractions can be implemented (eg Process , address pace)[1]
  • Exokernels should avoid resource managment except when required protection ( allocation , revocation , ownership)[1]
  • application based resource managment is the best way to build fexible efficient flexible systems [1]
• Expose allocation[1]
  • allow LibOs to request physical resources [1]
  • resource allocation should not be automatic, the LibOS should participate in every single allocation decision [1]
• Expose Names[1]

An exokernel should export physical names.
Physical names are efficient, since they remove a level of indirection
otherwise required to translate between virtual and physical names.
Physical names also encode useful resource attributes. For example,
in a system with physically-indexed direct-mapped caches, the name
of a physical page (i. e., its page number) determines which pages
it conflicts with. Additionally, an exokemel should export bookkeeping
data structures such as freelists, disk arm positions, and
cached TLB entries so that applications can tailor their allocation
requests to available resources,

(copy and pasted from [1]) and one under stand what this mean's --Asoknack 03:35, 9 October 2010 (UTC)

• Expose Revocation [1]
  • use visible revocation protocol [1]
  • allows well behaved LibOS to preform application level resource managment [1]
  • Visible revocation allows the LibOS to choose what instance of the resource to release (what makes thing "Visible" does it just mean every LibOS can see it ) --Asoknack 03:43, 9 October 2010 (UTC)

Policy

• LibOS handle resource policy decisions
• Exokernels have a policy to decided between competeing LibOS (Priority , share of resources)
  • it enforces this threw allocation and deallocation (every thing can achived threw this even what block to write and such)

Secure Bindings

• Used by the exokernel to allow the LibOS to bind to resources [1]
• Allow's the seperation of protection and resource use [1]
• only checks authorization durning bind time [1]
  • Application's with complex need's for resources only authorized durining bind.[1]
• acces checking is done during acces time and there is no need to understand complex accese need's during acces[1]
  • (this mean's that the exokernel check's once to make shure an application has authorization once approved, when the application tries to use the resource the exokernel is only concerned about policy conflict's)--Asoknack 18:20, 9 October 2010 (UTC)
  • alow's the kernel to protect the resources with out understanding what the resource is [1]
• three way's to implement
• Hardware Mechanisms [1]
• Software caching [1]
• Downloading application code [1]

Downloading Code to the Kernel

References

[1] Engler, D. R., M. F. Kaashoek, and J. O'Toole. "Exokernel." ACM SIGOPS Operating Systems Review 29.5 (1995): 251-66. Association for Computing Machinery. Web. 8 Oct. 2010. <http://portal.acm.org/citation.cfm?id=224076>.

Unsorted

Exokernel- Minimalistic abstractions for developers Exokernels can be seen as a good compromise between virtual machines and microkernels in the sense that exokernels can give that low level access to developers similar to direct access through a protected layer and at the same time can contain enough hardware abstraction to allow similar benefit of hiding the hardware resources to application programs. Exokernel – fewest hardware abstractions to developer Microkernel - is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system Virtual machine is a simulation of any or devices requested by an application program Exokenel – I’ve got a sound card Virtual Machine – I’ve got the sound card you’re looking for, perfect virtual match Microkernel – I’ve got sound card that plays Khazikstan sound format only MicroKernel - Very small, very predictable, good for schedualing (QNX is a microkernel - POSIX compatable, benefits of running linux software like modern browsers)

This is some ideas I've got on this question, please contribute below -Rovic

Outlining some main features here as I see them.

I found that the exokernel was an even lower-level design than the microkernel, closer to the hardware without abstraction. They have the same architecture with the basic functionality contained in the kernel to manage everyone. As the exokernel "gives" the resource to the application it can use the resource in isolation of other applications (until forced to shared) much like VMs receive their resources, either partitioned or virtualized, and execute as if its running on its own machine. There is this similar notion of partitioning the resources among applications/OS and allowing them to take control of what they have.

I'll locate some references later on. --Slay 15:00, 7 October 2010 (UTC)

Maybe we can have an introduction - paragraph or so on each type - then similarities - differences - and the compromise. I am going to do some research and writing this weekend and I will put some up -- Jslonosky

btw in my page (i guess you can call it that) i have some resources i have found --Asoknack 15:50, 8 October 2010 (UTC) - Wow, nice man. I will go ahead and write up the descriptive paragraphs on each kernel and virtual machine if no one minds. --Jslonosky