briefintroduction

ABriefIntroductiontotheDesignofUBIFS

Documentversion0.1

byAdrianHunter27.3.2008

becauflash

memorymustbeeradbeforeitcanbewrittento,anditcantypicallyonlybewrittenoncebefore

eblocksweresmallandcouldbeeradquickly,thentheycould

betreatedthesameasdiskctors,anentireerablock,era

it,andwritebackupdateddatatypicallytakes100timeslongerthansimplywritingtheupdateddata

rwords,forsmallupdates,in-place

updatescantake100timeslongerthanout-of-placeupdates.

isupdatedout-of-place,erablocks

begintocontainamixtureofvaliddataanddatawhichhasbecomeobsoletebecauithasbeen

ally,thefilesystemwillrunoutofemptyerablocks,sothat

rtowritenew

datasomewhere,

processofidentifyinganerablockwithalotofobsoletedata,andmovingthevaliddatatoanother

erablock,iscalledgarbagecollection.

rtogarbagecollectan

erablock,theoppositeof

ystemusuallystartswithafilenameandhas

ecollectionstartswithdatathatmaybelongtoany

file(ornofileifitisobsolete)andmustfindwhichfile,ifany,tosolvethat

mbinationofdataandmetadatais

derecordswhichfile(morespecificallyinodenumber)thatthenode

belongstoandwhatdata(forexamplefileofftanddatalength)

JFFS2andUBIFSfollowanode-structureddesign,thatenablestheirgarbagecollectorstoread

erablocksdirectlyanddeterminewhatdataneedstobemovedandwhatcanbediscarded,andto

updatetheirindexesaccordingly.

ThebigdifferencebetweenJFFS2andUBIFSisthatUBIFSstorestheindexonflashwhereas

JFFS2storestheindexonlyinmainmemory,rebuildingitwhenthefilesystemismounted.

PotentiallythatplacesalimitonthemaximumsizeofaJFFS2filesystem,becauthemounttime

asdesignedspecificallyto

overcomethatlimitation.

Unfortunately,storingtheindexonflashisverycomplexbecautheindexitlfmustbeupdated

epartoftheindexisupdatedout-of-place,thenanyotherpartsoftheindex

thatreferencetheupdatedpart,n,inturn,thepartsthatreference

utiontothiseminglynever-endingcascadeofupdatesisto

uawanderingtree.

InthecaoftheUBIFSwanderingtree(whichistechnicallyaB+tree),onlytheleavesofthetree

ernalelementsofthetree

,anindexnoderecordstheon-

BIFSwanderingtreecanbeviewedashavingtwoparts.

Atoppartconsistingofindexnodesthatcreatethestructureofthetree,andabottompart

partisreferredtosimplyasthe

tetothefilesystemconsistsofcreatinganewleafnodeandaddingit,orreplacing

rtodothat,theparentindexnodemustalsobereplaced,andits

parent,berofindexnodesthathavetobereplacedis

ustremainsthequestionofhowtoknowwheretherootofthe

S,thepositionoftherootindexnodeisstoredinthemasternode.

Themasternodestoresthepositionofallon-flashstructuresthatarenotatfixedlogicalpositions.

Themasternodeitlfiswrittenrepeatedlytologicalerablocks(LEBs)e

sphysicalerablocks(PEBs)toLEBs,soLEBoneand

twocanbeanywhereontheflashmedia(strictlyspeaking,theUBIdevice),howeverUBIalways

blocksareudinordertokeeptwocopiesofthemasternode.

Thisisdoneforthepurpoofrecovery,becautherearetwosituationsthatcancauacorrupt

stisthattherecouldbealossofpoweratthesameinstantthatthe

ondisthattherecouldbedegradationorcorruptionofthe

irstca,recoveryispossiblebecauthepreviousversionofthemaster

econdca,recoveryisnotpossiblebecauitcannotbedetermined

latterca,aurspaceutilityprogramwould

beneededtoanalyzeallthenodesonthemediaandattempttofixorrecreatecorruptormissing

twocopiesofthemasternodemakesitpossibletodeterminewhichsituationhas

arin,andrespondaccordingly.

ThefirstLEBisnotLEBone,

sumple,theflash

geometry(erablocksize,numberoferablocktc)ent,

thereisonlyonesituationwherethesuperblocknodegetsrewritten,whichiswhenanautomatic

rentlyhasaverylimitedabilitytoresizetogrowbigger,butonlytoa

chanismisneededbecauthe

actualsizeofaflashpartitionvariesduetotheprenceofavariablenumberofbaderablocks.

,themaximumnumberoferablocksis

specifiedandtheimagerecordsthis,andtheactualnumberoferablocksud,inthesuperblock

IFSismountedonapartition(actuallyaUBIvolume),ifthenumberof

erablocksisgreaterthanthatrecordedinthesuperblocknodeandlessthanthemaximumnumber

oferablocks(alsorecordedinthesuperblocknode),thentheUBIFSfilesystemisautomatically

resizedtofitthepartition(UBIvolume).

ThereareinfactsixareasinUBIFSwhopositionisfixedatthetimethefilesystemiscreated.

erblock

nodeisalwaysatofftzero,andthesuperblockLEBiswrittenusingUBI'satomicLEBchange

ftareaisthe

ral,thotwoLEBscontainidentical

ternodeiswrittentosuccessivepositionsineachLEBuntilthereisnomorespace,at

whichpointtheLEBsareunmappedandthemasternodewrittenatofftzero(whichautomatically

causUBItomapaneradLEB).NotethatthemasternodeLEBsarenotbothunmappedatthe

sametimebec

otherUBIFSareasare:thelogarea(orsimplythelog),theLEBpropertiestree(LPT)area,the

orphanareaandthemainarea.

ThelogisapartofUBIFS'pooftheUBIFSjournalistoreducethefrequency

,thattheindexconsistsofthetoppartofthewanderingtree

thatismadeupofonlyindexnodes,andthattoupdatethefilesystemaleafnodemustbeaddedor

replacedidbe

veryinefficientiftheon-flashindexwereupdatedeverytimealeafnodewaswritten,becaumany

ofthesameindexnodeswouldbewrittenrepeatedly,particularlytowardsthetopofthetree.

Instead,UBIFSdefinesajournalwhereleafnodesarewrittenbutnotimmediatelyaddedtotheon-

attheindexinmemory(eTNC)ically,whenthejournalis

consideredreasonablyfull,mitprocessconsistsofwritingthenew

versionoftheindexandthecorrespondingmasternode.

TheexistenceofthejournalmeansthatwhenUBIFSismounted,theon-flashindexisout-of-date.

Inordertobringitup-to-date,

,thatthebiggerthejournal,the

longeritwilltaketoreplay,therhand,abigger

thejournalneedstobecommittedlessoften,e

rogram,soitcanbechontomeetthe

r,bydefaultUBIFSdoesnotemployitsfastunmountoption,

usthejournaltobealmostemptywhenthe

filesystemismountedagain,oodtrade-off

becauthecommitprocessitlfisgenerallyquitequick,takingafractionofacond.

d,thejournal

containstwotypesof

tstartnode,thatrecordsthatacommithasbegun,andreferencenodesthat

EBsare

calledbuds,isafinitesizeandmaybe

commit,thereferencenodesthatrecordedtheprevious

positionofthejournalarenolongerneededsothetailofthelogiradatthesameratethatthe

hecommit-startnoderecordsthestartofcommit,theendof

commitisdefinedtobewhenthemasternodeiswritten,becauthemasternodepointstothenew

ommitisnotcompletedbecauthefilesystemisunmounted

uncleanly(oss),thenthereplayprocessreplaysboththeoldandnewjournal.

stcomplicationisthattheleafnodes

eUBIFSemploysamultiheadedjournal,theorderthattheleaf

nodeswerewrittenisnotsimplytheorderthatthecorrespondingbuderablockswerereferenced

rtoquenceleafnodes,everynodecontainsa64-bitquencenumberthat

layfirstreadsalltheleafnodesinthejournal

-treeisthenprocesdinorder

andthe(in-memory)indexupdatedaccordingly.

Thenretwokinds

eletionwhichcorrespondstothedeletionoffilesanddirectories,anddirectory

S,inodeshavea

correspondinginodenodewhichrecordsthenumberofdirectoryentrylinks,moresimplyknown

inodeisdeleted,aninodenodewithalinkcountofzeroiswrittentothe

ca,insteadofaddingthatleafnodetotheindex,itisremovedfromtheindex

aofdeleteddirectory

entries,adirectoryentrynodeiswrittentothejournalbuttheinodenumberthatthatdirectory

entrypreviouslyreferredto,attherearetwoinodenumbersassociatedwitha

denumberoftheparentdirectory,andtheinodenumberofthefileorsub-

elatterinodenumberthatisttozerointhe

ereplayprocessadirectoryentrywithaninodenumberof

zero,itremovesthatentryfromtheindexinsteadofaddingit.

Truncations,ofcour,,atruncationcanextendthelengthofa

FS,

filesystemparlance,extendingthelengthofafileviatruncationcreatesa"hole"whichisan

oesnotindexholesand

daholeisanindexentrythatisnotthere.

WhenUBIFSlooksuptheindexandfindsnoindexentry,itisdefinedtobeaholeandthezeroed

therhand,truncationsthatreducethelengthofafilerequirethat

artohavethat

happen,trunca

replayprocessthonodesbyremovingthecorrespondingindexentries.

ThenextcomplicationisthatthereplaymustbringtheLEBpropertiestree(LPT)areaup-to-date.

LEBpalues

are:freespace,at

indexnodesandnon-indexnodesarenevermixedwithinthesameerablock,henceanindex

erablockisanerablockthatcontains(only)indexnodes,andanon-indexerablockisan

erablockthatcontains(only)aceisthenumberofbytesattheendofan

erablockthathavenotbeenwrittentoyet,paceis

thenumberofbytestakenupbyobsoletenodesandpadding,thatcanpotentiallybereclaimedby

propertiesareesntialtofindspacetoaddtothejournal,orthe

index,imeanodeiswritten,thefree

imeanodeisobsoletedorapaddingnodeis

written,oratruncationordeletionnodeiswritten,dirtyspacemustbeincreadforthaterablock.

Whenanerablockisallocatedtotheindex,itmustberecordedsothat,forexample,anindex

erablockwithfreespaceisnotallocatedtothejournal-whichwouldcauindexandnon-index

,thereasonthatindexandnon-indexnodesmaynotbemixedhastodo

withbudgetingwhichisdescribedfurtheron.

Generallyspeaking,theindexsubsystemitlftakescareofinformingtheLEBproperties

plexitythatLEBpropertiesraisinthereplay

eindex,the

eindex,theon-flashLPTisout-of-dateatmount

n-flashLEBpropertiesofthe

laywillbegintoupdatethe

LEBproperties,howeversomeofthochangesoccurredbeforethegarbagecollection,andsome

ingatwhichpointthegarbagecollectionoccurred,thefinalLEB

rtohandlethat,thereplayinrtsareferenceintoitsRB-

treetoreprentthepointatwhichtheLEBwasaddedtothejournal(usingthequencenumberof

thelogreferencenode).ThatenablesthereplaytocorrectlyadjusttheLEBpropertyvalueswhen

thereplayRB-treeisappliedtotheindex.

Anoecordson

snot,thencertainerror

layisaffectedintwomain

,abuderablockmaybecorruptedbecauitwasbeingwrittenatthetimeofa

ly,

replayhandlesthosituationsbypassingtheerablocktotherecoverytotrytofixthenodesin

ilesystemismountedread-write,thentherecoverywilldothenecessary

way,theintegrityofarecoveredUBIFSfilesystemisasperfectasone

ilesystemismountedread-only,therecoveryis

deferreduntilitismountedread-write.

Thefinalcomplicationisthatsomeoftheleafnodesreferencedbytheon-flashindexmaynotexist

ppenswhenthenodeshavebeendeletedandtheerablockthatcontainedthem

lly,deletedleafnodesdonotaffectthereplay

r,oneaspectofthestructureoftheindexdoes

ppensbecauof

directoryentrynodes(andalsoextendedattributeentrynodes).InUBIFS,adirectoryconsistsof

totheindexis

doneusinganodekey,cas,thenodekey

ununately,in

thecaofdirectoryentries(andextendedattributeentries)theuniquelyidentifyinginformationis

thename,whichmaybequitelong(upto255charactersinthecaofUBIFS).Tosqueezethat

informationinto64-bits,thenameishashedintoa29-bitvaluewhichisnotuniquetothename.

Whentwonamesgivethesamehashvalue,itiscalledahashcollision(orsimplycollision).Inthat

ca,theleafnodesmustbereadtoresolvethecollisionbycomparingthenamesstoredintheleaf

sout

oryentrynodes(andextendedattributeentrynodes)areonlyever

addedorremoved-t

theoutcomeofthenamecomparisonisknowneventhoughthenodecontainedoneofthenamesis

dingahashed-keynode,movingahashed-key

node,therewillalwaysbeamatch,eithertoanexistingnode,ortoamissingnodethathasthe

rtoprovidethisspecialindexupdatingforthereplay,aparatetoffunctions

isud(denotedinthecodebytheprefix"fallible").

Afterthelogarea,eofthelogareaisdefinedwhenthefilesystemis

ent,thesizeoftheLPTareais

automaticallycalculatedbadontheLEBsizeandmaximumLEBcountspecifiedwhenthefile

elogarea,thelogarea,

tion,theamountof

LEBputionisto

theLPTareaismuchlikeaminiaturefilesystem

tsownLEBproperties-thatis,theLEBpropertiesoftheLEBproperties

area(calledltab).tsownnodestructurethatpacks

r,liketheindex,theLPTareaisupdated

eon-flashindexandtheon-flashLPTreprentwhatthefilesystem

ferencebetweenthatandtheactualstateofthefilesystem,

isreprentedbythenodesinthejournal.

TheLPTactual

smallmodelisudw

thatca,LPTgarbagecollectionconsistsofjustwritingthewholetable,whichthereforemakesall

aofthebigmodel,dirtyLPTerablocksare

lectedforLPTgarbagecollection,whichconsistsofmarkingthenodesinthatLEBasdirty,and

thenwritingoutonlythedirtynodes(aspartofthecommit).Also,inthecaofthebigmodel,a

tableofLEBnumbersissavedsothattheentireLPTdoesnottobescannedlookingforempty

mallmodel,itisassumedthatscanningtheentire

tableisnotslowbecauitissmall.

that

efficient,indexnodesarecachedinmemoryinastructurecalledthetreenodecache(TNC).The

TNCisB+treethatisnode-for-nodethesameastheon-flashindex,withtheadditionofallchanges

rwaytolookatthat,

isthataznodewhenitison-flashiscalledanindexnode,andanindexnodewhenitisinmemory

ookupisdoneontheindex,justtheindex

nodeneedstobe

changed,itismarkedasdirtywhichpinsitinmemoryuntilthenextcommitatwhichtimeit

imeUBIFSmemoryshrinkermaydecidetofreecleanznodesinthe

TNC,sothattheamountofmemoryneededisproportionaltothesizeofthepartsoftheindexthat

areinu,tion,hangingoffthebottomoftheTNCisaleaf-

nodecache(LNC)whichisudonlyfordirectoryentries(andextendedattributeentries).The

LNCisneededtoe

theLNCisattachedtotheTNCiteffectivelygetsshrunkwhentheTNCdoes.

TheTNCisfurthercomplicatedbythedesiretomakethecommithaveaslittleimpactaspossible

at,stpartis

commitstartthecommitmaphoreisdownforwriting,which

time,theTNCsubsystemmakesalistofthedirty

ecommitmaphore

isrelead,andanewjournalbeginstobeud,ondpart

commitend,TNCwritesthenewindexnodesbutit

TNCcanbeupdatedsimultaneouslyasthenewindexis

accomplishedbymarkingtheznodeswhicharebeingcommittedas

dethatisbeingcommittedneedstobechanged,itiscopiedsothatthe

tion,thecommitismostlyrunbyUBIFS

backgroundthreadsothaturprocesswaitaslittleaspossibleforthecommittorun.

NotethatLPTfollowsthesamecommitstrategyasTNCandtheyarebothwanderingtrees

implementedasB+trees,resultinginanumberofsimilaritiesinthecodeofLPTandTNC.

sthasalreadybeen

mentioned:UBIFShasanon-flashindex,

conddifferenceisimplied:UBIFSrunsontopoftheUBIlayerwhichrunsontopoftheMTD

subsystem,enefitsfromthewear-levelingand

errorhandlingofUBIatthecostoftheflashspace,

thirdimportantdifferenceisthatUBIFSallowswriteback.

WritebackisaVFSfacilitythatallowswrittendatatobecachedandnotwrittenimmediatelytothe

kesthesystemmoreresponsiveandpotentiallymoreefficientbecauupdatesto

ficultywithsupportingwritebackisthatitrequires

thatthefilesystemknowhowmuchfreespaceisavailablesothatthecacheisneverbiggerthanthe

verydifficultforUBIFStodetermine,soanentiresubsystemcalled

ficultiesareforveralreasons.

etheamountof

compressionisnotknowninadvance,theamountofspaceneededisnotknowninadvance.

Budgetingmustassumetheworstca,r,inmany

rtoovercomethat,budgetingwillbegintoforcewriteback

whenitdetectsthatthereisinsufficientspace.

Thecondreasonthatbudgetingisdifficultisthatgarbagecollectionisnotguaranteedtobeable

a

ofNANDflash,rablockismade

allstheNANDpagesizetheminimal

I/eUBIFSgarbagecollectionprocessoneerablockatatime,ifthedirtyspaceis

lessthantheminimalI/Osize,itcannotbereclaimed-itwillendupaspaddinginthelastNAND

edirtyspaceinanerablockislessthantheminimalI/Osize,thatspaceiscalled

aceisnotreclaimable.

aceiswhenthedirtyspaceinanerablockisless

orstca,thefilesystemmaybefullofnodesofmaximum

sizeandgarbagecollectionwillnotresultinpiecesoffreespacethatarelargeenoughforanother

,intheworstca,darkspaceisnotreclaimable,andinthebestcaitis

udgetingmustassumetheworstcaandsobothdeadspaceanddarkspace

r,ifthereisinsufficientspacebutalotofdarkspace,

budgetingwillitlfrungarbagecollectiontoeifitreclaimsmorefreespace.

Thethirdreasonthatbudgetingisdifficultisthatcacheddatamaybeobsoletingdatastoredon

rornotthatisthecaisnotalwaysknown,andwhatthedifferenceincompression

anotherreasonthatbudgetingforceswritebackwhenit

tertryingwriteback,garbagecollectionandcommittingthe

journal,willbudgetinggiveupandreturnENOSPC(thenospaceerrorcode).

OfcourthatmeansthatUBIFSbecomeslesfficientasthefilesystembecomesclortobeing

,becauitis

lesslikelythatthereisanemptyerablockthathasbeeneradinthebackground,andmorelikely

thatgarbagecollectionwillhavetorun.

Thefourthreasonthatbudgetingisdifficultisthatdeletionsandtruncationsneedtowritenew

thefilesystemisreallyoutofspace,itbecomesimpossibletodeleteanything

becauthereisnoroomtowriteadeletioninodenode,entthat

situation,UBIFSalwayskeepsbackasomespaceandalwaysallowsdeletionsandtruncations.

anisaninodenumberwhoinode

ppenswhenanopenfileis

deleted(unlinked)ormalcourofeventstheinodewouldbe

rinthecaofanuncleanunmount,orphansneedtobe

nuncleanunmount,theorphans'inodesmustbedeletedwhichmeanither

scanningtheentireindexlookingforthem,

implementsthelatterapproach.

Theorphan

imumnumberis

eoftheorphanareashouldbesothatitcanholdthemaximumnumberoforphansthatare

beroforphansthatcanfitinaLEBis:

(leb_size-32)/8

Forexample:a15872byteLEBcanfit1980orphansso1LEBmaybeenough.

inode'slinkcountdropstozero,theinodenumber

orphans

thatareintheorphantreewhenthecommitisrun,arewrittentotheorphanareain1ormore

rphanareaisfull,salwaynough

spacebecauvalidationpreventstheurfromcreatingmorethanthemaximumnumberof

orphansallowed.

nareacontainsthenodesthatmakeupthefile

reaLEBmaybeanindexerablockoranon-indexerablock.

Anon-indexerablockmaybeabud(partofthejournal)ybe

atcontainscommittednodescanstillbecomeabudif

udLEBhasanofftfromwhichjournalnodesbegin,althoughthat

offtisusuallyzero.

UBIFSSourceFileList

ting

einitialization,mountingandunmounting

tmanagement

essionmanagement

ginglf-checks

ginglf-checksheader

toryoperations

perations

rablocksforvariouspurpo.g.G.C.

gecollection

/O

2compatibleextendedattributeioctls

alupdates

keyrelatedfunctions

operties

opertiestree(LPT)

lpt_mmit

rnode

dinlinefunctions

ns

ery

y

ltfilesystemcreationandsuperblocknode

alpurpoerablockscanner(G.C.)

yshrinkerforTNC

operations

odecache(TNC)

tnc_mmit

naldefinitions

-flashstructuresanddefinitions

dedattributes

UBIFSGlossary

B+treeKindoftreeudforUBIFSwanderingtree.

eheadprovides

theintegrityandrecoverabilityofUBIFSbykeepingallinode

nodesanddirectoryentrynodesinquence.

budgetingEstimationoffreespace.

budAnerablockudbythejournal.

cnodeEitherapnodeorannnode.

commitProcessbywhichtheindexisupdated.

commitstartnodeNodewrittentothelogwhenacommitstarts.

commonheaderCommonheaderofallnodetypexceptnodesintheLPT

area.

iallyUBIFScould

havemorethanonedataheadwhichwouldassistinkeeping

datanodesforeachfilegroupedtogetherratherthan

rprentlythereisonlyonedatahead.

directoryentrynodeAnodethatcontainsadirectoryentry.

dirtyspaceSpacetakenuponflashbyobsoletenodes,paddingnodesand

paddingbytes.

erablockThesmallestunitofflashmemorythatcanbeindividually

erad.

extendedattributeentrynodeAnodethatcontainsthenameandinodenumberofan

extendedattribute(samestructureasadirectoryentry).

freeableLEBALEBinthemainareathatcontainsonlyfreespaceanddirty

space.

freespaceSpaceonflashthatcanbewrittento.

garbagecollectionTheprocessofreclaimingdirtyspacetomakefreespace.

rtomove

andreindexnodes,thegarbagecollectorjustfeedsthemback

throughthejournal.

garbagecollectionLEBnumberLEBrervedforgarbagecollection(mustalwaysbeoneLEB

rerved),alsoknownasgc_lnum.

indexThetoppartoftheUBIFSwanderingtreeconsistingofindex

nodes.

indexLEBALEBthatcontains(only)indexnodes.

ainsthe

keysandon-flashpositionsofitschildnodes.

S,aninodemaybearegular

file,adirectory,asymboliclink,aspecialfile,oranextended

attribute(xattr)valueholder.

nodehas

exactlyone(non-obsolete)inodenode.

in-the-gapsmethodWhenthefilesystembecomesfull,theindexcannotgrowin

done

bywritingindexnodesin-the-gapscreatedbyobsoleteindex

nodes.

JFFS2JournalingFlashFileSystem2whichisthequintesntial

linuxflashfilesystem,howeveritisnotscalableandthe

prentlimitofitsusageis1GiB.

journalThejournalislikeaminiatureJFFS2filesystem,storing

nodeswithoutanon-flashindex,sothatindexupdatescanbe

FS2thejournalmustbescanned

atmounttime.

journalheadThepositionon-flashwherethenextnodewillbewritten.

UBIFSadoptsamultiheadedjournalwithtwomainheads:the

baheadandthedatahead.

exstoresthepositionofall

nodes,aybefoundbylookingupits

isa64-bitvaluewhofirst32bits

t3bitsarenodetype,andthe

lso

supportsthepossibilityofchangingthekeyformatandallows

forupto128-bitsforthekey.

LEBLogicalerablockthatismappedtoaphysicalerablock

(PEB)byUBI.

LEBpropertiesMainareaLEBshavethreeimportantvaluesthatarerecorded

EBpropertiesare:amountoffreespace,

amountofdirtyspace,andwhethertheLEBcontainsindex

nodes.

LNCLeafnodecacheudtostoredirectoryentriesandextended

attributeentries

logThepartofthejournalthatrecordswherethebudsare.

LPTLEBpropertiestree,awanderingtreeudtostoreLEB

properties.

mainareaLEBsthatareudfordataandtheindex.

masternodeThenodethatcontainsthepositionsofon-flashstructures.

minimalI/OunitThesmallestunitofflashmemorythatcanbeindividually

written.

heurspaceprogramthatcreatesUBIFSimages.

devicelayerforflash

memories.

nodeThelogicalcomponentofnode-structuredflashfilesystems

likeJFFS2andUBIFS.

nnodeInternalnodeoftheLPT.

orphanareaAreaforstoringtheinodenumbersofdeletedbystillopen

inodes,neededforrecoveryfromuncleanunmounts.

orphannodeThenodeudtostoreorphaninformation.

paddingbytesByteswrittenwhenthespacetopadistoosmallforapadding

node.

paddingnodeAnodewrittentofillspace,usuallytotheedgeofaminimal

I/Ounit.

PEBPhysicalerablockthatismappedtoalogicalerablock

(LEB)byUBI.

pnodeLeafnodeoftheLPTwhichcontainstheactualLEBproperty

values.

recoveryThefunctionsbywhichUBIFSrepairsitlfafteranunclean

unmount.

replayTheprocessbywhichUBIFSreindexesthenodesinthe

journalwhenthefilesystemismounted.

referencenodeLognodesthatstoretheLEBnumbersofbudsandtheir

offt.

shrinkerAlinuxfacilitytherequeststhatsomememorybefreedif

asashrinkerthatfreescleanznodesfrom

theTNC.

superblocknodeThenodethatrecordsfilesystemparametersthatalmostnever

change.

TNCTreeNodeCache,UBIFSindexinmemory.

truncationnodeAnodethatrecordswhenafileistruncatedandbecomes

smaller.

UBIUnsortedBlockImagesmodulethatprovideswear-leveling,

bad-blockhandling,andthecreationoflogicalvolumes

mappinglogicalerablockstophysicalerablocks.

UBIFSUBIFileSystem.

uncleanunmountWhenthefilesystemdoesnothaveachancetowriteall

cacheddataandmetadata,forexamplebecauofalossof

power.

wanderingtreeAtreethatmovesinawaytoallowout-of-placeupdates.

formtheTNC.