Chapter 10: File-System Interface Dr. Varin Chouvatut. Operating System Concepts 8 th Edition,

Transcription

1 Chapter 10: Fie-System Iterface Dr. Vari Chouvatut Operatig System Cocepts 8 th Editio, Siberschatz, Gavi ad Gage 2010

2 Chapter 10: Fie-System Iterface Fie Cocept Access Methods Directory Structure Fie-System Moutig Fie Sharig Protectio Operatig System Cocepts 8 th Editio 10.2 Siberschatz, Gavi ad Gage 2010

3 Objectives To expai the fuctio of fie systems To describe the iterfaces to fie systems To discuss fie-system desig tradeoffs, icudig access methods, fie sharig, fie ockig, ad directory structures To expore fie-system protectio Operatig System Cocepts 8 th Editio 10.3 Siberschatz, Gavi ad Gage 2010

4 Fie Cocept Cotiguous ogica address space Types: Data umeric character biary Program Operatig System Cocepts 8 th Editio 10.4 Siberschatz, Gavi ad Gage 2010

5 Fie Structure Noe - sequece of words, bytes Simpe record structure Lies Fixed egth Variabe egth Compex Structures Formatted documet Reocatabe oad fie Ca simuate ast two with first method by isertig appropriate cotro characters Who decides: Operatig system Program Operatig System Cocepts 8 th Editio 10.5 Siberschatz, Gavi ad Gage 2010

6 Fie Attributes Name oy iformatio kept i huma-readabe form Idetifier uique tag (umber) idetifies fie withi fie system Type eeded for systems that support differet types Locatio poiter to fie ocatio o device Size curret fie size Protectio cotros who ca do readig, writig, executig Time, date, ad user idetificatio data for protectio, security, ad usage moitorig Iformatio about fies are kept i the directory structure, which is maitaied o the disk Operatig System Cocepts 8 th Editio 10.6 Siberschatz, Gavi ad Gage 2010

7 Fie Operatios Fie is a abstract data type Create Write Read Repositio withi fie Deete Trucate Ope(F i ) search the directory structure o disk for etry F i, ad move the cotet of etry to memory Cose (F i ) move the cotet of etry F i i memory to directory structure o disk Operatig System Cocepts 8 th Editio 10.7 Siberschatz, Gavi ad Gage 2010

8 Ope Fies Severa pieces of data are eeded to maage ope fies: Fie poiter: poiter to ast read/write ocatio, per process that has the fie ope Fie-ope cout: couter of umber of times a fie is opeed to aow remova of data from ope-fie tabe whe ast processes coses it Disk ocatio of the fie: cache of data access iformatio Access rights: Each process opes a fie i a access mode Operatig System Cocepts 8 th Editio 10.8 Siberschatz, Gavi ad Gage 2010

9 Ope Fie Lockig Provided by some operatig systems ad fie systems Mediates access to a fie Madatory or advisory: Madatory access is deied depedig o ocks hed ad requested Advisory processes ca fid status of ocks ad decide what to do Operatig System Cocepts 8 th Editio 10.9 Siberschatz, Gavi ad Gage 2010

10 Fie Lockig Exampe Java API import java.io.*; import java.io.chaes.*; pubic cass LockigExampe { pubic static fia booea EXCLUSIVE = fase; pubic static fia booea SHARED = true; pubic static void mai(strig arsg[]) throws IOExceptio { FieLock sharedlock = u; FieLock excusivelock = u; try { RadomAccessFie raf = ew RadomAccessFie("fie.txt", "rw"); // get the chae for the fie FieChae ch = raf.getchae(); // this ocks the first haf of the fie - excusive excusivelock = ch.ock(0, raf.egth()/2, EXCLUSIVE); /** Now modify the data... */ // reease the ock excusivelock.reease(); Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

11 Fie Lockig Exampe Java API (cot) } } // this ocks the secod haf of the fie - shared sharedlock = ch.ock(raf.egth()/2+1, raf.egth(), SHARED); /** Now read the data... */ // reease the ock sharedlock.reease(); } catch (java.io.ioexceptio ioe) { System.err.prit(ioe); }fiay { if (excusivelock!= u) excusivelock.reease(); if (sharedlock!= u) sharedlock.reease(); } Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

12 Fie Types Name, Extesio Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

13 Access Methods Sequetia Access Direct Access = reative bock umber read ext write ext reset o read after ast write (rewrite) read write positio to rewrite read ext write ext Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

14 Sequetia-access Fie A fie ca be reset to the begiig; ad o some systems, a program may be abe to skip forward or backward records. Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

15 Simuatio of Sequetia Access o Direct-access Fie Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

16 Exampe of Idex ad Reative Fies (A exampe of other access methods) Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

17 Directory Structure A coectio of odes cotaiig iformatio about a fies Directory Fies F 1 F 2 F 3 F 4 F Both the directory structure ad the fies reside o disk Backups of these two structures are kept o tapes Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

18 Disk Structure Disk ca be subdivided ito partitios Disks or partitios ca be RAID protected agaist faiure Disk or partitio ca be used uformatted (raw) without a fie system, or formatted with a fie system Partitios aso kow as miidisks, sices Etity cotaiig a fie system kow as a voume Each voume cotaiig a fie system aso cotais iformatio about the fies i the system. This iformatio is kept i a device directory or voume tabe of cotets As we as geera-purpose fie systems there are may specia-purpose fie systems, frequety a withi the same operatig system or computer Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

19 A Typica Fie-system Orgaizatio Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

20 Operatios Performed o Directory Search for a fie Create a fie Deete a fie List a directory Reame a fie Traverse the fie system Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

21 Orgaize the Directory (Logicay) to Obtai: Efficiecy ocatig a fie quicky Namig coveiet to users Two users ca have same ame for differet fies The same fie ca have severa differet ames Groupig ogica groupig of fies by properties, (e.g., a Java programs, a games, ) Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

22 Sige-Leve Directory A sige directory for a users Namig probem Groupig probem Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

23 Two-Leve Directory Separate directory for each user Path ame Ca have the same fie ame for differet user Efficiet searchig No groupig capabiity Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

24 Tree-Structured Directories Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

25 Tree-Structured Directories (Cot) Efficiet searchig Groupig Capabiity Curret directory (workig directory) cd /spe/mai/prog type ist Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

26 Tree-Structured Directories (Cot) Absoute or reative path ame Creatig a ew fie is doe i curret directory Deete a fie rm <fie-ame> Creatig a ew subdirectory is doe i curret directory mkdir <dir-ame> Exampe: if i curret directory /mai mkdir cout mai prog copy prt exp cout Deetig mai deetig the etire subtree rooted by mai Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

27 Acycic-Graph Directories Have shared subdirectories ad fies Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

28 Acycic-Graph Directories (Cot.) Two differet ames (aiasig) If dict deetes ist dagig poiter Soutios: Backpoiters, so we ca deete a poiters Variabe size records a probem Backpoiters usig a daisy chai orgaizatio Etry-hod-cout soutio New directory etry type Lik aother ame (poiter) to a existig fie Resove the ik foow poiter to ocate the fie Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

29 Geera Graph Directory Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

30 Geera Graph Directory (Cot.) How do we guaratee o cyces? Aow oy iks to fie ot subdirectories Garbage coectio Every time a ew ik is added use a cyce detectio agorithm to determie whether it is OK Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

31 Fie System Moutig A fie system must be mouted before it ca be accessed A umouted fie system (i.e. Fig (b)) is mouted at a mout poit Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

32 (a) Existig. (b) Umouted Partitio Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

33 Mout Poit Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

34 Fie Sharig Sharig of fies o muti-user systems is desirabe Sharig may be doe through a protectio scheme O distributed systems, fies may be shared across a etwork Network Fie System (NFS) is a commo distributed fie-sharig method Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

35 Fie Sharig Mutipe Users User IDs idetify users, aowig permissios ad protectios to be per-user Group IDs aow users to be i groups, permittig group access rights Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

36 Fie Sharig Remote Fie Systems Uses etworkig to aow fie system access betwee systems Mauay via programs ike FTP Automaticay, seamessy usig distributed fie systems Semi-automaticay via the word wide web Ciet-server mode aows ciets to mout remote fie systems from servers Server ca serve mutipe ciets Ciet ad user-o-ciet idetificatio is isecure or compicated NFS is stadard UNIX ciet-server fie sharig protoco CIFS is stadard Widows protoco Stadard operatig system fie cas are trasated ito remote cas Distributed Iformatio Systems (distributed amig services) such as LDAP, DNS, NIS, Active Directory impemet uified access to iformatio eeded for remote computig Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

37 Fie Sharig Faiure Modes Remote fie systems add ew faiure modes, due to etwork faiure, server faiure Recovery from faiure ca ivove state iformatio about status of each remote request Stateess protocos such as NFS icude a iformatio i each request, aowig easy recovery but ess security Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

38 Fie Sharig Cosistecy Sematics Cosistecy sematics specify how mutipe users are to access a shared fie simutaeousy Simiar to Ch 7 process sychroizatio agorithms Ted to be ess compex due to disk I/O ad etwork atecy (for remote fie systems Adrew Fie System (AFS) impemeted compex remote fie sharig sematics Uix fie system (UFS) impemets: Writes to a ope fie visibe immediatey to other users of the same ope fie Sharig fie poiter to aow mutipe users to read ad write cocurrety AFS has sessio sematics Writes oy visibe to sessios startig after the fie is cosed Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

39 Protectio Fie ower/creator shoud be abe to cotro: what ca be doe by whom Types of access Read Write Execute Apped Deete List Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

40 Access Lists ad Groups Mode of access: read, write, execute Three casses of users RWX a) ower access RWX b) group access RWX c) pubic access Ask maager to create a group (uique ame), say G, ad add some users to the group. For a particuar fie (say game) or subdirectory, defie a appropriate access. ower group pubic chmod 761 game Attach a group to a fie chgrp G game Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

41 Widows XP Access-cotro List Maagemet Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

42 A Sampe UNIX Directory Listig Operatig System Cocepts 8 th Editio Siberschatz, Gavi ad Gage 2010

43 Ed of Chapter 10 Operatig System Cocepts 8 th Editio, Siberschatz, Gavi ad Gage 2010