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中科大操作系统课件04.ppt

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MODERNOPERATINGSYSTEMSThirdEditionANDREWS.TANENBAUMChapter4FileSystemsEssentialrequirementsforlong-terminformationstorage:Itmustbepossibletostoreaverylargeamountofinformation.Theinformationmustsurvivetheterminationoftheprocessusingit.Multipleprocessesmustbeabletoaccesstheinformationconcurrently.Thinkofadiskasalinearsequenceoffixed-sizeblocksandsupportingreadingandwritingofblocks.Questionsthatquicklyarise:Howdoyoufindinformation?Howdoyoukeeponeuserfromreadinganother’sdata?Howdoyouknowwhichblocksarefree?filesFilenamingFigure4-1.Sometypicalfileextensions.Figure4-2.Threekindsoffiles.(a)Bytesequence.(b)Recordsequence.(c)Tree.FileTypesFigure4-3.(a)Anexecutablefile.(b)Anarchive.FileAccessFigure4-4a.Somepossiblefileattributes.StructstatFileattributesFileOwnerThemostcommonsystemcallsrelatingtofiles:Figure4-5.Asimpleprogramtocopyafile.Figure4-5.Asimpleprogramtocopyafile.Figure4-6.Asingle-leveldirectorysystemcontainingfourfiles.Figure4-7.Ahierarchicaldirectorysystem.Figure4-8.AUNIXdirectorytree.PathnamesPathnamesSystemcallsformanagingdirectories:DirectoryoperationFileSystemImplementationFileSystemLayoutFigure4-9.Apossiblefilesystemlayout.Figure4-10.(a)Contiguousallocationofdiskspacefor7files.(b)ThestateofthediskafterfilesDandFhavebeenremoved.ContiguousAllocationFigure4-11.Storingafileasalinkedlistofdiskblocks.LinkedlistallocationFigure4-12.Linkedlistallocationusingafileallocationtableinmainmemory.LinkedListAllocationUsingaTableinMemoryFigure4-13.Anexamplei-node.i-nodesFigure4-14.(a)Asimpledirectorycontainingfixed-sizeentrieswiththediskaddressesandattributesinthedirectoryentry.(b)Adirectoryinwhicheachentryjustreferstoani-node.Figure4-15.Twowaysofhandlinglongfilenamesinadirectory.(a)In-line.(b)Inaheap.Figure4-17.(a)Situationpriortolinking.(b)Afterthelinkiscreated.(c)Aftertheoriginalownerremovesthefile.Figure4-20.Percentageoffilessmallerthanagivensize(inbytes).Figure4-21.Thesolidcurve(left-handscale)givesthedatarateofadisk.Thedashedcurve(right-handscale)givesthedis