Chapter 10: File-System InterfaceSlide 2Storage ManagementObjectivesFile ConceptSlide 6File AttributesFile OperationsTypical File OperationsSlide 10File Operations – The Process ItselfOpen File TablesOpen File Basic InformationOpen File LockingFile Locking Example – Java APIFile Locking Example – Java API (cont)File Types – Name, ExtensionSlide 18File StructureFile Structure – not recognizable formats…Internal File StructureSlide 22Slide 23Access MethodsSlide 25Slide 26Sequential-access FileSimulation of Sequential Access on a Direct-access FileExample of Index and Relative FilesSlide 30Slide 31End 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 – Storage ManagementProcess / processor managementMemory management Storage managementDisk storage – the primary medium for primary, online storage.Contains files – collections of related items defined by the 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; blocks at a time.Disk Access – sometimes access sequentially; sometimes randomly.Some file systems dedicated; some sharedSome transfer data asynchronously; others synchronously.Differ greatly in speed – many parameters as cited above.This chapter: the File System Interface.10.4Silberschatz, Galvin and Gagne ©2005Operating System ConceptsObjectivesObjectives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 protection10.5Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile ConceptFile ConceptA File System consists of two parts:Files – storage of dataStored on a sequential or some kind of direct access storage device.Directory Structure – organizes the information about the files.Size, location, logical record length, block size, format, ownership, security, paths to files/directories,l 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.Almost all storage devices are non-volatileMagnetic tapesMagnetic disksOptical disks,Jump drivesCDs / DVDs ….Many more…10.6Silberschatz, 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.Can be somewhere in between – variable length recordsBright Lights files overseas?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. Files – data files – many forms and structuresI like to differentiate between a file’s organization and how it may be accessed.They are not the same, as we shall see.Files - program files – source programs, object files – understandable by the linker and executable files – ready for loader to bring into memory.These files, when created, contain relocation and linkage information that linkers and loaders need to create executables and/or to load the file for execution.Much of the data about programs and data files revolves simply as how they are used!10.7Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFile AttributesFile AttributesName – This is the only information kept in human-readable formIs independent of the process and system that created it.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; Information about files like those mentioned above are kept in the directory structure, which is maintained on the diskNames: example: VTOC (Volume Table of Contents – IBM) or some general directory structure name…10.8Silberschatz, 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 and use), andOperations that can be performed on the data – dependent upon how it is implemented.Let’s look at the six basic functions that can be performed on most files.10.9Silberschatz, Galvin and Gagne ©2005Operating System ConceptsTypical File OperationsTypical File OperationsCreate – Need to allocate spaceAdd an entry in the disk directory; load data onto the storage device.Write – “System call” supplies name of file and data to be written.A pointer usually needs to be available to point to the place where the next ‘item’ is to be written; pointer updated.Read – Another system call specifies file name, where in memory the read data is to be placed, and, using a read pointer, locates the data to be read.Pointer needs to be updated to point to the ‘next’ item to be read.Pointer for read and write is called a ‘current file-position