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1、第 2 讲：OS Architecture&Structure第五节：Exokernel Xok+ExOSProblem.InsightApplications Know Better Than OSApplication demands vary widely.IdeasGive un-trusted applications as muchcontrol over physical resources as possibleTo force as few abstraction as possible ondevelopersseparate protection from managem
2、ent.IdeasGive un-trusted applications as muchcontrol over physical resources as possibleTo force as few abstraction as possible ondevelopersseparate protection from management.Solution.ChallengesTracking ownership of resourcesEnsuring resource protectionRevoking resource access.TechniquesSecure bind
3、ingVisible revocationAbort protocol.Techniques secure bindingIt is a protection mechanism that decouples authorization from actualuse of a resourceSecure binding techniquesHardware mechanismSoftware cachingDownloading application code.Techniques visible resource revocationA way to reclaim resources
4、and break their(application&resources)secure bindingAn exokernel uses visible revocation formost resourcestraditional OS have performed revocationinvisibly.dialogue between an exokernel and alibrary OSlibrary OS should organize resourcelists.Techniques the abort protocolIf a library OS fails to resp
5、ond quickly,the secure bindings need to bebroken“by force”The abort protocolAn exokernel simply breaks all securebindings to the resource and informs thelibrary operating system.Techniques library OSManage OS abstractions at application levelIPC AbstractionsApplication-level Virtual MemoryRemote Communication.ImplementationPrototype(Xok/ExOS)Exokernel:Xok on x86,Aegis runs on DECLibrary OS:ExOS,fundamental OSabstractions at application level.Performance.Performance.Performance.Performance.Performance.Performance.Performance.