Rules for Filters (both Legacy and Mini).ppt

RulesforFilters(bothLegacyandMini)1©:SynchronizationDon’tissuefilesystemcallswhileholdingalock(FastMutex,EResource,PushLock)MaycausethesystemtodeadlockEspeciallywithotherfilterspresent2©:SynchronizationMinimizethesynchronizationyourfilterusesLeadingcauseofperformancedegradationWhenpossibleusedshared/exclusivesemanticsPushLocksareefficient,veryhardtodebugadeadlock3©:TopLevelIrpDon’tissuefilesystemcallsifIoGetTopLevelIrp()returnsanon-NULLvalueMaycausethesystemtodeadlockThefailurestatusreturnedfromafilesystemoperationwhileprocessingarecursiveIOoperation(TopLevelIrpreturnsnon-NULLvalue)willbepropagatedbacktotheTopLeveloperationFltGetVolumeInformation()example4©:AccessingUserBuffersIfaMDLisdefinedalwaysuseittogetasystemaddressforthebufferMmGetSystemAddressForMdlSafe()Iftheoperationisnotbuffered,esseswithtry/exceptFLTFL_CALLBACK_DATA_SYSTEM_BUFFERAllFastIOoperationsmustbetreatedasifmethodneitherbufferingwasused5©:PostOperationCallbacksPostOperationcallbackroutinesmaybecalledatDPCIRQLCodepostOperationroutineasiftheyarealwayscalledatDPClevelDon’tissueFileIOoperationsCan’pletionProcessingWhenSafe()6©:PostOperationCallbacksCannotcallFltGetXxxContext()pletionProcessingWhenSafe()CancallFltReleaseContext()atDPClevel7©:PostOperationCallbacksCallingFltGetFileNameInformation()fromapostOperationcallback:()pletionProcessingWhenSafe()TopLevelIrpmaystillbesetbyfilesystem8©