YaffsDirect

YaffsDirectInterfaceCharlesManning2012-07-22ThisdocumentdescribestheYaffsDirectInterface(YDI),whichallowsYaffstobesimplyintegratedwithembeddedsystems,withorwithoutanRTOS.TableofContents1Background.............................................................................................................................22Licensing.................................................................................................................................33WhatareYaffsandYaffsDirectInterface?.............................................................................34WhyuseYaffs?........................................................................................................................45SourceCodeandYaffsResources..........................................................................................46SystemRequirements..............................................................................................................57HowtointegrateYaffswithanRTOS/Embeddedsystem......................................................57.1SourceFiles......................................................................................................................67.2IntegratingthePOSIXApplicationInterface...................................................................77.3RTOSIntegrationInterface..............................................................................................88YaffsNANDModel................................................................................................................98.1NANDModelconsiderationsforYaffs1........................................................................108.2NANDModelforYaffs2................................................................................................109NANDConfigurationandAccessInterface..........................................................................129.1Commonconfigurationitems(Yaffs1andYaffs2).........................................................129.2CommonAccessFunctions(Yaffs1andYaffs2)............................................................139.3Yaffs1AccessFunctions.................................................................................................149.4Yaffs2AccessFunctions.................................................................................................1410UsingthePOSIXfilesysteminterface...............................................................................1510.1DifferencetoWindowsPOSIX-likeinterfaces............................................................1510.2Fundamentalconcepts..................................................................................................1610.3Errorcode.....................................................................................................................1610.4Links–thehardkind(notsymboliclinks)..................................................................1710.5Symboliclinks..............................................................................................................1810.6Handle-basedfilehandling...........................................................................................1910.7Changingfilesize.........................................................................................................2010.8Getting/settinginformationaboutfiles.........................................................................2110.9Changingthedirectorystructureandnames................................................................2210.10Searchingdirectories..................................................................................................2310.11Mountcontrol.............................................................................................................2310.12Other...........................................................................................................................2411Example:yaffs_readdir()andyaffs_stat()...........................................................................241BackgroundThepurposeofthisdocumentistodescribetheinterfacingoftheYaffsDirectInterface(YDI)aswellastoprovidesufficientinformationtoallowapreliminaryevaluationofYaffs.ThisdocumenttriestofocusontheissuesimportanttothesystemintegratorwithoutgettingtoodetailedabouthowYaffsworks.Otherdocumentsprovideanin-depthdiscussionofhowYaffsworks.Page2/25ofYaffsDirectInterface,2012-07-052LicensingYaffswasoriginallyreleasedforLinuxundertheGNUPublicLicense(GPL).Variousembed-deddeveloperssoonidentifiedthatYaffswouldbeidealfortheirapplications,butwerenotabletouseGPLbasedcodeintheirsystems.AlephOnehasalternativelicensingarrange-mentstosupportsuchapplications.3WhatareYaffsandYaffsDirectInterface?YaffsstandsforYetAnotherFlashFileSystem.Yaffswasthefirstfilesystemdesigned,fromthegroundup,forNANDstorage.In2002AlephOnesetouttoidentifyfilesystemoptionsforusingNANDFlashasafilesys-tem.Variousfilesystemsavailableatthetimewereevaluatedandallwerefoundlackinginonewayoranother.Theneedforasu