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1、Chapter8.RootFilesystemSetupHavingbuilttherootfilesystemandpreparedthetarget'sstoragedevice,wearenowreadytosetuptherootfilesystemasitwillbeusedonthetarget.First,weneedtoselectafilesystemtypefortherootfilesystem.Then,weneedtoconverttherootfilesystem'scontenttotheselectedfilesystemformatorinstallt
2、herootfilesystemonadeviceformattedfortheselectedfilesystemtype.Thischapterbeginsbydiscussingthebasicfilesystemselectioncriteria.ThisisfollowedbyasectiondescribinghowtouseNFStotransferfilesystemimagestothetarget'sflash,atechniqueweuseofteninthischapter.Wethenconcentrateonthesetupofrootfilesystems
3、foruseonCRAMFS,JFFS2,NFTL,andRAMdisks,respectively.Finally,wediscusstheuseofTMPFSformountingcertaindirectories,andhowtoupdateanembeddedsystem'srootfilesystemdynamically.Attheendofthischapter,theonlyissueremainingtogettingafullyfunctionalembeddedsystemwillbethesetupandconfigurationofthebootloader
4、.Iwillcovertheseissuesinthenextchapter.8.1SelectingaFilesystemSelectingafilesystemtypeforyourrootfilesystemisadelicateprocess.Thefinaldecisionisoftenacompromisebetweenthefilesystem'scapabilitiesandthetarget'spurpose.Itis,forexample,uselesstochooseafilesystemthatprovidespersistentwritestorage,suc
5、hasJFFS2,ifthetargetneverneedstopermanentlystoreanydata.Forsuchatarget,afilesystemwithnopersistentstorage,suchasCRAMFS,isamuchbetterchoice.Furthermore,youmaywanttoconsiderusingmanyfilesystemsforthesamesystem.Asystemthatneedsreadandwriteaccesstotemporaryfilesonly,forinstance,couldhavemostofitsroo
6、tfilesystemmountedonCRAMFSwhilehavingits/var/tmpdirectorymountedonTMPFSoraRAMdisk,andits/tmpbeingasymboliclinkto/var/tmp.8.1.1CharacterizingFilesystemsToselectthebestfilesystemorbestcombinationoffilesystemsforacertainapplication,weneedtohaveaminimumsetofcharacteristicsthatcanbeusedtocomparefiles
7、ystems.Table8-1summarizesthecharacteristicsofthefilesystemstypicallyusedinembeddedLinuxsystems.Foreachfilesystemtype,thesearethequestionsusedtocharacterizeit:WriteCanthefilesystembewrittento?Persistent24Doesthefilesystempres
