Ice 2 Layout

8/12/2019 Ice 2 Layout

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The IceFileSystem 2.x Disk Layout

By Leif Salomonsson (c) 2011

Last updated: June 2 2011.

Contents:

Introduction. Conventions. eta !eaders. eta "#$ects. %&tents. 'dmin Space. Constants. unctions.


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Introduction

Ice ileSystem layout is e&tent #ased *+#it ,it- c-ec summedmeta data and a meta level $ournal.

ain space allocator is #ased on /LS al orit-m adapted for on disstora e.

'll metadata e&cept e&tent -eaders are located in speciale&tents called pools and use a local #itmap to eep tracof free meta space. etadata is very compact.

esi n oals and priorities

*+#it dis filesystem supportin a -i - num#er of useful features

#y a desi n prioritised li e follo,in :1 3elia#ility 2 Scala#ility 4 %fficiency + Speed

eatures

64bit file/partition/extent sizes (actually very close to 2^63 bytes). No self imposed fra mentation oflar e files unless t!ere is not enou ! conti ious space available.

"ll metadata on dis# is c!ec#summed. $!is means any errors on dis# %ill be detected a lot &uic#er. 'eta level ornallin . ardlin#s (directory and file)* softlin#s* file comments.

+upports bloc#sizes from ,-2 bytes to 32 i . 0ilesystem does not et slo%er for lar er partitions (scales very %ell)* or %!en !eavily fra mented. No limit in 1 of files/dirs in partition/dirs. ecycle directory. "utomatically truncated lo files and file c!an e lo . astes only -2 # (and preallocates anot!er -2 # for meta space) for filesystem administration data*

re ardless of partition size.


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Conventions'll meta data stores information in #i endian format.

'll on dis pointers e&press a #yte offset relative to t-e startof t-e volume.

'll fields in all structures descri#ed are of t-e unsi ned inte er ind,it- si5es ran ein from 1 to 6 #ytes or array of unsi ned inte er ind.

ield types:

p*+ 7 *+#it pointerp42 7 42#it pointeri*+ 7 *+#it inte eri42 7 42#it inte eri1* 7 1*#it inte er

i6 6#it inte er


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eta !eaders

'll meta o#$ects starts ,it- a meta -eader structure t-e 8meta8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6

SI9%" 1*

selfadr:pointer to our selves.

c-ec sum:

total sum of all 42#it ,ords (,it- 8c-ec sum8 field itselfcleared) t-at ma e up t-e ,-ole o#$ect (si5e of o#$ect in8metasi5e8 field).

metasi5e:total si5e of meta o#$ect.

reserved:5ero.

metata :inte er descri#in t-e type of meta o#$ect.

'dditionally all meta t-at is stored in meta pools -ave one e&tra 8#mapadr8 field. /-e8pmeta8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6#mapadr p*+

SI9%" 2+

#mapadr:pointer to t-e 8#itmap8 o#$ect.


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eta "#$ects

/-e 8filesys8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6creation i*+totalsi5e i*+rootentry p42rootnode p42root-as-ta# p42recyclednode p42lo filenode p42fsversion i42

fsrevision i42#loc si5e i42reserved2 ;2< i42-as-type i42e&tinfo p42$ournal p42startofe&tents p42endofe&tents p*+po,erta#s ;*+< p42ori =selfadr p*+reserved ;1>< i*+

metasi5e:?12

metata :/'@= IL%SAS

creation:time of creation e&pressed in microseconds since startof time ;1..*4 areactually used #ut all po,ers s-ould still #e initialised.

pad:

5ero.

ta#le:ree e&tents are c-ained to et-er in a dou#ly

lin ed list and t-e ta#le contains pointers to t-efirst e&tent in eac- list or 5ero if empty.

/-e entry o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6#mapadr p*+lin p*+parent p*+namee&t p*+ne&t-lin p*+type i6fla s i6namelen i1*dirne&t p*+dirprev p*+-as-ne&t p*+-as-prev p*+name ;4*


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pointer to parent entry. 5ero if root.

namee&t:pointer to 8namee&t8 o#$ect if filename e&ceeds 4* c-aracterselse 5ero.

ne&t-lin :

ne&t -ard lin . pointer used to lin -ard lin s for anentry to et-er. ori inal entry is not part of t-is lin a e.

type:%/A %= . eit-er %/A %=!'3 %H/3A or %/A %=S" /%H/3A.

fla s:% L'@= . only one fla for no,: % L'@=!I %H.

namelen:total len t- of filename in c-aracters.

dirne&t:

pointer to ne&t entry in directory or 5ero if last.

dirprev:pointer to previous entry in directory or 5ero if first.

-as-ne&t:pointer to ne&t entry in -as- ta#le lin a e.

-as-prev:pointer to previous entry in -as- ta#le lin a e.

name:array containin t-e (first 4* c-aracters of) filename.

/-e 8namee&t8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6#mapadr p*+str ;1000


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selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6

#mapadr p*+softtime p*+str ;>>2


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%it-er H/A %= IL% or H/A %= I3.

rsrvd:5ero.

fla s:efined fla s are H L'@=L"@ IL% and H L'@=3%CACL% I3.

prot#its:rotection #its. Li e ami a protection #its #ut

=,it-out= t-e inversion of t-e lo,er ni##le.

reserved:5ero.

o,nerinfo: Li e ami a o,nerinfo. ori entry:

pointer to t-e 8ori inal8 entry.

addentries:pointer to t-e first -ard lin entry or 5ero.

modified:modification timestamp e&pressed in micro seconds sincestart of time.

data=first:pointer to first filedata e&tent or 5ero.

data=last:pointer to last filedata e&tent or 5ero.

dir=first:pointer to first entry in directory or 5ero.

dir=last:pointer to last entry in directory or 5ero.

e&tleft:num#er of #ytes left in last e&tent.

numentries:num#er of entries in directory. not really used #yanyt-in #ut s-ould #e updated any,ay.

filesi5e:t-e current filesi5e if H/A %= IL%.

-as-:pointer to 8-as-ta#8 o#$ect if H/A %= I3.

comment:pointer to 8comment8 o#$ect or 5ero.

rsrvd4:5ero.


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/-e 8-as-ta#8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6

metata i6#mapadr p*+parent p*+ta#le ;12+


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%&tents

'll e&tents starts ,it- t-e 8e&tent8 o#$ect -eader ,-ic- in turnstarts ,it- t-e 8meta8 o#$ect -eader.

/-e 8e&tent8 o#$ect:

selfadr p*+c-ec sum i42metasi5e i1*metarsrvd i6metata i6e&tsi5e i*+e&t=prev p*+data=ne&t p*+data=prev p*+dataofs i42

data=e&tnum i42data=node p*+MN unions NMran e=ne&t p*+ data=ne&tran e=prev p*+ data=prevreuse=ne&t p*+ data=ne&treuse=prev p*+ data=prev#itmap p*+ dataofs

metasi5e:*+

selfadr:al,ays #loc si5e ali ned.

metasi5e:al,ays *+

metata :/ype of e&tent (%/'@= )./-ere are t-ree types of e&tents:%/'@= 3%%: free space.%/'@= %/' ""L: 126KiB meta pool.%/'@= IL% '/': file data e&tent.

e&tsi5e:si5e of t-is e&tent in #ytes. al,ays #loc si5e ali ned.

e&t=prev:pointer to previous e&tent #y placement on dis .

Oif metata %/'@= IL% '/'

data=ne&t:pointer to ne&t filedata e&tent.

data=prev:

pointer to previous filedata e&tent.dataofs:


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Start of filedata relative to start of e&tent descri#ed in #ytes.%it-er SI9%" e&tent (*+) for files t-at fits in (#loc si5e 7 SI9%" e&tent)or #loc si5e for lar er files.

data=e&tnum:filedata e&tent num#er startin at 0.

data=node:pointer #ac to t-e 8node8 o#$ect.

Oendif

Oif metata %/'@= 3%%

ran e=ne&t:pointer to ne&t free e&tent in t-is ran e.

ran e=prev:pointer to previous free e&tent in t-is ran e.

Oendif

Oif metata %/'@= %/' ""L

reuse=ne&t:pointer to ne&t non full metapool e&tent.

reuse=prev:pointer to previous non full metapool e&tent.

#itmap:pointer to 8#itmap8 o#$ect. 'L 'AS selfadr P *+.

Oendif


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'dmin Space

/-e si5e of adminspace is 126KiB. It is located at #e inninof partition and starts ,it- t-e 8icestart8 structure:

ice0 i42fsys i42filesys p42

ice0:t-e ma ic ,ord I =IC% S= ISK

fsys:t-e ma ic ,ord 8 SAS8

filesys:

pointer to t-e 8filesys8 o#$ect.

eta o#$ects in admin space:

1 ilesys1 %&tinfo*+ o,erQs1 Journal

Bac ed up o#$ects.

' volume ends ,it- a copy of t-e root -as-ta#le o#$ect. 's of revision 4 also t-e filesys o#$ect is #ac ed up directly in front of t-e root -as-ta#le #ac up. Bot- -as-ta#le and filesys

#ac up -ave t-eir 8selfadr8 field c-an ed to #ac up location. /-e 8filesys8 o#$ect eeps a #ac up of t-e ori inal 8selfadr8 in

its 8ori =selfadr8 field.


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ConstantsI =IC% S= ISK 0&+>+4+?02

/'@=H"H% 0

%/'@= 3%% 1%/'@= %/' ""L 2%/'@= IL% '/' 4%/'@=3%S%3R% +

/'@= IL%SAS ?/'@=%H/3A */'@=H" % E/'@=H' %% / 6/'@=C" %H/ >/'@=S" /H' % 10/'@=!'S!/'B 11/'@=H"/DS% 12

/'@= " %3 14/'@=J"D3H'L 1+/'@=BI/ ' 1?/'@=% /IH " 1*/'@=3%S%3R% 1E

%/' ""LSI9% 102+ N 126' IHS 'C% 102+ N 126

%/'BL"CKSI9% 126 %/'BL"CK 'SK 12E %/'BL"CKS!I / E

' BI/ ' IH % 41 BI/ ' L"H@S 42 BI/ ' 3%S%3R% 12

%/A %=!'3 %H/3A 0 %/A %=S" /%H/3A 1

% L'@=!I %H 1' %H/3AH' %BA/%S 4*

H/A %= IL% 0H/A %= I3 1H L'@=L"@ IL% 1

H L'@=3%CACL% I3 2

!'S!/'B%H/3I%S 12+

' H' %% /S/3BA/%S 1000 ' S" /H' %S/3BA/%S >>2 ' C" %H/S/3BA/%S 1000

IH " %3 *' " %3 *4

3'H@%S %3 " %3 *+ 3'H@%S %3 " %3S!I / *

IL%SAS3%S%3R% 1>


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!'S!/A %=H% 2 !'S!/A %=H% =C'S% 4

% /IH "3%S%3R% 21

' J"D3H'LSI9% 42E*6

' %/'SI9% 102+


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unctions

unctions are ,ritten in % lan ua e #ut s-ould not#e too -ard to translate into C or somet-in else.

/-e directory entry name -as-in al orit-m:Case sensitive:

3"C -as- is HameHe,Case12+(name: /3 /" C!'3)% i v 0:L"H@ c

G et a small seed from num#er of c-aracters!IL% c : name;v

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Ice 2 Layout