操作系统原理10

Chapter10:FileSystemInterface沈卓炜h@[e-mail]四牌楼校区文正楼南205，83790819-802九龙湖校区计算机楼316Chapter10:File-SystemInterfaceCapte0eSysteteace„FileConcept„FileConcept„AccessMethods„DirectoryStructureFilStMti„FileSystemMounting„FileSharingg„ProtectionSoutheastUniversity10.2OperatingSystemConceptsFileConcepteCocept„Contigoslogicaladdressspace„Contiguouslogicaladdressspace„Types:‹Data‹Data9numeric9character9character9binary‹P‹ProgramSoutheastUniversity10.3OperatingSystemConceptsFileStructureNfdbt„None-sequenceofwords,bytes„SimplerecordstructureSimplerecordstructure‹Lines‹Fixedlength‹Fixedlength‹Variablelength„ComplexStructures‹Formatteddocument‹Formatteddocument‹Relocatableloadfile„Cansimulatelasttwowithfirstmethodbyinsertingappropriatecontrolcharacters.SoutheastUniversity10.4OperatingSystemConceptsgppp„Whodecides?FileAttributes„Name–onlyinformationkeptinhuman-dblfreadableform.„Type–neededforsystemsthatsupportypyppdifferenttypes.„Locationpointertofilelocationondevice„Location–pointertofilelocationondevice.„Size–currentfilesize.SoutheastUniversity10.5OperatingSystemConceptsFileAttributes(Cont.)„Protection–controlswhocandoreading,writing,executing.„Timedateanduseridentification–data„Time,date,anduseridentificationdataforprotection,security,andusagemonitoringmonitoring.„Informationaboutfilesarekeptinthedirectorystructure,whichismaintainedonthedisk.thedisk.SoutheastUniversity10.6OperatingSystemConceptsFileOperationseOpeatos„Create„Create„Write„Read„Repositionwithinfile–fileseek„Repositionwithinfile–fileseek„Delete„TruncateSoutheastUniversity10.7OperatingSystemConceptsFileOperations(Cont.)eOpeatos(Cot)„Open(F)searchthedirectorstrctre„Open(Fi)–searchthedirectorystructureondiskforentryFi,andmovethecontentofentrytomemory.„Close(Fi)–movethecontentofentryFiintditttdikmemorytodirectorystructureondisk.SoutheastUniversity10.8OperatingSystemConceptsFileTypes–Name,Extensioneypesae,tesoSoutheastUniversity10.9OperatingSystemConceptsAccessMethods„SequentialAccess„DirectAccessSoutheastUniversity10.10OperatingSystemConceptsSimulationofSequentialAccessonaDirect-accessFileaccessFileSoutheastUniversity10.11OperatingSystemConceptsExampleofIndexandRelativeFilFilesSoutheastUniversity10.12OperatingSystemConceptsDirectoryStructure„disksaresplitintooneormorepartitions.„eachpartitioncontainsinformationbtfilithiitaboutfileswithinit„TheinformationiskeptinentriesindiditltbladevicedirectoryorvolumetableofcontentsSoutheastUniversity10.13OperatingSystemConceptsATypicalFile-systemOitiOrganizationSoutheastUniversity10.14OperatingSystemConceptsOperationsPerformedonDitDirectory„Searchforafile„Searchforafile„Createafile„DeleteafileLitdit„Listadirectory„Renameafile„TraversethefilesystemSoutheastUniversity10.15OperatingSystemConceptsOrganizetheDirectory(Logically)toObtain„Efficiency–locatingafilequickly.„Naming–convenienttousers.‹Twouserscanhavesamenamefordifferent‹Twouserscanhavesamenamefordifferentfiles.‹Thesamefilecanhaveseveraldifferent‹Thesamefilecanhaveseveraldifferentnames.„Grouping–logicalgroupingoffilesbyproperties,(e.g.,allJavaprograms,allpp,(g,pg,games,…)SoutheastUniversity10.16OperatingSystemConceptsSingle-LevelDirectorySgeeeectoy„Asingledirectoryforallusers„Asingledirectoryforallusers.NamingproblemGroupingproblempgpSoutheastUniversity10.17OperatingSystemConceptsTwo-LevelDirectoryoeeectoy„Separatedirectoryforeachuser.•Pathname•Canhavethesamefilenamefordifferentuser•Canhavethesamefilenamefordifferentuser•Efficientsearching•NogroupingcapabilitySoutheastUniversity10.18OperatingSystemConceptsNogroupingcapabilityTree-StructuredDirectorieseeStuctuedectoesSoutheastUniversity10.19OperatingSystemConceptsTree-StructuredDirectories(Cont.)eeStuctuedectoes(Cot)„Efficientsearching„Efficientsearching„GroupingCapability„Currentdirectory(workingdirectory)‹cd/spell/mail/prog‹typelistypSoutheastUniversity10.20OperatingSystemConcepts„Absoluteorrelativepathname„Creatinganewfileisdoneincurrentdirectory.„Deleteafilermfile-nameSoutheastUniversity10.21OperatingSystemConceptsTree-StructuredDirectories(Cont.)„Creatinganewsubdirectoryisdoneincurrentgydirectory.mkdirdir-namemkdirdir-nameExample:ifincurrentdirectory/mailmkdircountmailprogcopyprtexpcountSoutheastUniversity10.22OperatingSystemConceptsDeleting“mail”⇒deletingtheentiresubtreerootedby“mail”.Acyclic-GraphDirectoriescyccGapectoes„Havesharedsubdirectoriesandfilesfiles.SoutheastUniversity10.23OperatingSystemConceptsAcyclic-GraphDirectories(Cont.)cyccGapectoes(Cot)„Todifferentnames(aliasing)„Twodifferentnames(aliasing)„Ifdictdeletescount⇒danglingpointer.Solutions:Solutions:‹Backpointers,sowecandeleteallpointers.‹Entry-hold-countsolution.SoutheastUniversity10.24OperatingSystemConceptsGeneralGraphDirectoryGeeaGapectoySoutheastUniversity10.25OperatingSystemConceptsGeneralGraphDirectory(Cont.)GeeaGapectoy(Cot)„Hodoegaranteenoccles?„Howdoweguaranteenocycles?‹Allowonlylinkstofilenotsubdirectories.‹Garbagecollection.‹Everytimeanewlinkisaddeduseacycle‹Everytimeanewlinkisaddeduseacycledetectionalgorithmtodeterminewhetherit