现代操作系统 Chapter ppt课件.ppt

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1、Chapter4FilesystemsContents4.1Files4.2Directories4.3FileSystemImplementation4.4FileSystemManagementandOptimization4.5ExampleFileSystemsFileSystemsEssentialrequirementsforlong-terminformationstorage:Itmustbepossibletostoreaverylargeamountofinformation.Theinformationmustsurvivetheter

2、minationoftheprocessusingit.Multipleprocessesmustbeabletoaccesstheinformationconcurrently.FileSystemsFilesarelogicalunitsofinformationcreatedbyprocesses.ThatpartoftheOSdealingwithfilesisknownasthefilesystem.4.1Files4.1.1FilenamingWhenaprocesscreatesafile,itgivesthefileaname.Whenthe

3、processterminates,thefilecontinuestoexistandcanbeaccessedbyotherprocessesusingitsname.Therulesoffilenaming(文件命名规则)Fileextension(文件扩展名)Figure4-2.Threekindsoffiles.(a)Bytesequence.(b)Recordsequence.(c)Tree.4.1.2Filestructure64.1.3FileTypesRegularfile(普通文件)ASCIIfilesBinaryfilesSpecial

4、file(特殊文件)Characterspecialfile:arerelatedtoinput/outputandusedtomodelserialI/OdevicesBlockspecialfile:areusedtomodeldisks4.1.4FileaccessSequentialaccess(顺序存取)Aprocesscouldreadallthebytesorrecordsinafileinorder,startingatthebeginning,butcouldnotskiparoundandreadthemoutoforder.Random

5、access(随机存取)Thebytesorrecordsinthesefilescanbereadinanyorder.4.1.5FileattributesFigure4-4.Somepossiblefileattributes.4.1.6FileOperationsCreateDeleteOpenCloseReadWriteAppendSeekGetattributesSetattributesRename104.1.7Anexampleprogramusingfilesystemcalls(1)11Anexampleprogramusingfiles

6、ystemcalls(2)124.2Directories1.Single-levelDirectorysystemsAdvantages:SimplicityTheabilitytolocatefilequicklyDirectories2.Hierarchical(层次)directorysystemsAdvantages:cangroupfilesinnaturalwaysDirectories3.PathnamesAbsolutepathname(绝对路径):consistingofthepathfromtherootdirectorytothefi

7、le.Italwaysstartattherootdirectoryandareunique.Relativepathname(相对路径):itisusedinconjunctionwiththeconceptoftheworkingdirectory.Directories4.DirectoryOperationsCreateDeleteOpendirClosedirReaddirRenameLinkUnlink4.3FileSystemImplementation4.3.1FileSystemLayout4.3.2ImplementingFiles4.3

8、.3Implementingdirectories4