Chapter10FileSystemInterfaceOperatingSystemConceptsChapter10:File-SystemInterfaceFileConceptAccessMethodsDirectoryStructureFileSystemMountingFileSharingProtectionOperatingSystemConceptsFileConceptContiguouslogicaladdressspace

Types:DatanumericcharacterbinaryProgramOperatingSystemConceptsFileStructureNone-sequenceofwords,bytesSimplerecordstructureLinesFixedlengthVariablelengthComplexStructuresFormatteddocumentCansimulatelasttwowithfirstmethodbyinsertingappropriatecontrolcharacters.Whodecides?OperatingSystemConceptsFileAttributesName–onlyinformationkeptinhuman-readableform.Type–neededforsystemsthatsupportdifferenttypes.Location–pointertofilelocationondevice.Size–currentfilesize.OperatingSystemConceptsFileAttributes(Cont.)Protection–controlswhocandoreading,writing,executing.Time,date,anduseridentification–dataforprotection,security,andusagemonitoring.Informationaboutfilesarekeptinthedirectorystructure,whichismaintainedonthedisk.OperatingSystemConceptsFileOperationsCreateWriteReadRepositionwithinfile–fileseekDeleteTruncateOperatingSystemConceptsFileOperations(Cont.)Open(Fi)–searchthedirectorystructureondiskforentryFi,andmovethecontentofentrytomemory.Close(Fi)–movethecontentofentryFiinmemorytodirectorystructureondisk.FileOperations(Cont.)FilelockingAdvisorylocking:requirescooperationfromtheparticipatingprocessesMandatorylocking:causesthekerneltocheckeveryopen,read,andwritetoverifythatthecallingprocessisn’tviolatingalockonthegivenfileOperatingSystemConceptsOperatingSystemConceptsFileTypes–Name,ExtensionOperatingSystemConceptsAccessMethodsSequentialAccess

DirectAccess

OperatingSystemConceptsSimulationofSequentialAccessonaDirect-accessFileOperatingSystemConceptsDirectoryStructuredisksaresplitintooneormorepartitions.eachpartitioncontainsinformationaboutfileswithinitTheinformationiskeptinentriesinadevicedirectoryorvolumetableofcontentsOperatingSystemConceptsATypicalFile-systemOrganizationOperatingSystemConceptsOperationsPerformedonDirectorySearchforafileCreateafileDeleteafileListadirectoryRenameafileTraversethefilesystemOperatingSystemConceptsOrganizetheDirectory(Logically)toObtainEfficiency–locatingafilequickly.Naming–convenienttousers.Twouserscanhavesamenamefordifferentfiles.Thesamefilecanhaveseveraldifferentnames.Grouping–logicalgroupingoffilesbyproperties,(e.g.,allJavaprograms,allgames,…)OperatingSystemConceptsSingle-LevelDirectoryAsingledirectoryforallusers.Namingproblem

GroupingproblemOperatingSystemConceptsTwo-LevelDirectorySeparatedirectoryforeachuser.PathnameCanhavethesamefilenamefordifferentuserEfficientsearchingNogroupingcapabilityOperatingSystemConceptsTree-StructuredDirectoriesOperatingSystemConceptsTree-StructuredDirectories(Cont.)Efficientsearching

GroupingCapability

Currentdirectory(workingdirectory)cd/spell/mail/progtypelistOperatingSystemConceptsAbsoluteorrelativepathnameCreatinganewfileisdoneincurrentdirectory.Deleteafile

rm<file-name>OperatingSystemConceptsTree-StructuredDirectories(Cont.)Creatinganewsubdirectoryisdoneincurrentdirectory.

mkdir<dir-name> Example:ifincurrentdirectory/mail

mkdircountmailprogcopyprtexpcountDeleting“mail”deletingtheentiresubtreerootedby“mail”.OperatingSystemConceptsAcyclic-GraphDirectoriesHavesharedsubdirectoriesandfiles.OperatingSystemConceptsAcyclic-GraphDirectories(Cont.)Twodifferentnames(aliasing)

Ifdictdeletescount

danglingpointer. Solutions:Backpointers,sowecandeleteallpointers.

Entry-hold-countsolution.Example:LinuxhardlinkandsoftlinkExplainedfollowing:/developerworks/cn/linux/l-cn-hardandsymb-links/OperatingSystemConceptsOperatingSystemConceptsGeneralGraphDirectoryOperatingSystemConceptsGeneralGraphDirectory(Cont.)Howdoweguaranteenocycles?Allowonlylinkstofilenotsubdirectories.Garbagecollection.EverytimeanewlinkisaddeduseacycledetectionalgorithmtodeterminewhetheritisOK.OperatingSystemConceptsFileSystemMountingAfilesystemmustbemountedbeforeitcanbeaccessed.Anunmountedfilesystem(I.e.Fig.11-11(b))ismountedatamountpoint.OperatingSystemConcepts(a)Existing.(b)UnmountedPartitionOperatingSystemConceptsMountPointExample:MountingisofileunderLinuxOperatingSystemConceptsmkdir-p/mnt/diskmount-oloopdisk1.iso/mnt/disk

umount/mnt/diskOperatingSystemConceptsFileSharingSharingoffilesonmulti-usersystemsisdesirable.Sharingmaybedonethroughaprotectionscheme.Ondistributedsystems,filesmaybesharedacrossanetwork.NetworkFileSystem(NFS)isacommondistributedfile-sharingmethod.OperatingSystemConceptsProtectionFileowner/creatorshouldbeabletocontrol:whatcanbedonebywhomTypesofaccessReadWriteExecuteAppendDeleteListOperatingSystemConceptsAccessListsandGroupsModeofaccess:read,write,executeThreeclassesofusers RWX a)owneraccess 7 111

b)groupaccess 6 110 c)publicaccess 1 001Askmanagertocreateagroup(uniquename),sayG,andaddsomeuserstothegroup.F