Chapter 10: File-System InterfaceSlide 2Storage ManagementStorage Management - moreObjectives of this Chapter:File ConceptSlide 7File Concept (continued)File AttributesFile OperationsTypical File OperationsTypical File Operations – moreSlide 13File Operations – The Process ItselfOpen File TablesOpen File Basic Information“Open File Locking”File Locking Example – Java APIFile Locking Example – Java API (cont)File Types – Name, ExtensionFile Types – Name, Extension - moreFile StructureFile Structure – not recognizable formats…Internal File StructureSlide 25Slide 26Access MethodsSlide 28Slide 29Sequential-access FileSimulation of Sequential Access on a Direct-access FileExample of Index Organization and Random AccessExample of Index Organization and Random AccessSlide 34Example of Relative FilesEnd of Chapter 10.1Chapter 10: File-System InterfaceChapter 10: File-System Interface10.2Silberschatz, Galvin and Gagne ©2005Operating System ConceptsChapter 10: File-System InterfaceChapter 10: File-System InterfaceChapter 10.1File ConceptAccess MethodsChapter 10.2Directory StructureFile-System MountingFile SharingProtection10.3Silberschatz, Galvin and Gagne ©2005Operating System ConceptsStorage ManagementStorage ManagementNew block – File Systems a.k.a. “Storage Management”An Operating System is often described as a program that manages processes, processors, memory, and storage.Listing these: operating systems control and manage:Processes (both user and system) Processors (the CPUs)Memory management (primary, cache, …) and Storage management (data, programs, directories used for access, etc. )10.4Silberschatz, Galvin and Gagne ©2005Operating System ConceptsStorage Management - moreStorage Management - moreDisk storage – primary medium for primary, online storage.Contains files – collections of related items defined by file creator.Normally grouped into directories for ease of use and reference.Organized in a variety of structures.Disk Access – sometimes character at a time; often blocks at a time.sometimes access sequentially; sometimes randomly.Some file systems dedicated; some sharedSome support data transfer data asynchronously; others synchronously.Differ greatly in speed – many parameters as cited above.This chapter: the File System Interface.10.5Silberschatz, Galvin and Gagne ©2005Operating System ConceptsObjectives of this Chapter:Objectives of this Chapter:To explain the function of file systemsTo describe the interfaces to file systemsTo discuss file-system design tradeoffs, including access methods, file sharing, file locking, and directory structuresTo explore file-system protection10.6Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile ConceptFile ConceptA File System consists of two parts:Files – the actual storage of data on a mediumStored on sequential or some kind of direct access storage device.Directory Structure – structures the information for access Size, location, logical record length, block size, format, ownership, security, paths to files / directories, etc.A file may be defined as a contiguous logical address space, which is mapped by the operating system onto some kind of physical devices.Note: ‘logical’ does not mean ‘physical.’Almost all storage devices are non-volatile (data remains when power is removed)Magnetic tapesMagnetic disksOptical disks,Jump drivesCDs / DVDs …. And others…10.7Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile ConceptFile ConceptTo a user, a file is the smallest allocation of logical secondary storage. All data is written to a ‘file.’Data may be numeric, alphabetic, alphanumeric, or binary.Can be free form (text) Can be rigidly formatted – records.Fixed length records; variable length records: Bright Lights application?Generally, a file is a sequence of bits, bytes, lines, or records … whose meaning is interpreted by the creator of the file and how it is used. “One man’s program is another man’s data.”10.8Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile Concept (continued)File Concept (continued)Data files – many forms and structuresDifferentiate between a file’s organization and how it may be accessed.not the sameProgram files – Source programs Object filesMay not be directly executableMay be understandable by a ‘linker.’Executable files May be ready for loader to bring into memory.Much of the data about programs and data files revolves simply as how they are used!10.9Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile AttributesFile AttributesName – Typically the only information kept in human-readable formUsually independent of the process and system that created it.Save for possible extensions or types, such as .doc or .ppt, etc.But names often are constrained by the operational environment.NIHPOO……. Each positions often means something very important in a commercial (non-academic environment.)Identifier – unique tag (number) identifies file within file systemNIHP00; System Code IH; Source programs: ‘N’; subsystem ‘P’Programs within subsystem: 00, 01, ….Type – needed for systems that support different types.c, .java. .cpp, .exe, .dll, .dat, .wpd, .doc, etc. .xls, .css. ….And bringing up certain ‘processes’ to process these files … by type.Location – pointer to file location on deviceSize – current file size - generally in bytes or blocks, especially blocks.Protection – controls who can do reading, writing, executingYes! Read, write, execute, Time, date, and user identification – data for protection, security, and usage monitoring – Maybe date last accesses; OPR; security.10.10Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile OperationsFile OperationsFile is an “abstract data type.”This means it has data which will be unique to its implementation (realization – how organized, and use – how accessed and processed), andFile operations that can be performed on the data – dependent upon how it is implemented.Accessed sequentially, randomly, etc. Let’s look at the six basic functions that can be performed on most