1 / 20

File Management System Objectives

File Management System Objectives. Meet the data management needs of the user Guarantee that the data in the file are valid Optimize performance Provide I/O support for a variety of storage device types Minimize the potential for lost or destroyed data

whilemina-stevenson
Download Presentation

File Management System Objectives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. File Management System Objectives • Meet the data management needs of the user • Guarantee that the data in the file are valid • Optimize performance • Provide I/O support for a variety of storage device types • Minimize the potential for lost or destroyed data • Provide a standardized set of I/O interface routines to user processes • Provide I/O support for multiple users in the case of multiple-user systems Operating System Concepts

  2. File Structure • None - sequence of words, bytes • Simple record structure • Lines • Fixed length • Variable length • Complex Structures • Formatted document • Relocatable load file • Can simulate last two with first method by inserting appropriate control characters. • Who decides: • Operating system • Program Operating System Concepts

  3. File Attributes • Name – only information kept in human-readable form. • Type – needed for systems that support different types. • Location – pointer to file location on device. • Size – current file size. • Protection – controls who can do reading, writing, executing. • Time, date, and user identification – data for protection, security, and usage monitoring. • Information about files are kept in the directory structure, which is maintained on the disk. Operating System Concepts

  4. File Operations • create • open • write • read • seek • delete • Truncate • close Operating System Concepts

  5. File Types – name, extension Operating System Concepts

  6. Access Methods • Provides a standard interface between applications and the file systems and devices that hold the data • Different access methods reflect different file structures and different ways of accessing and processing the data Operating System Concepts

  7. Sequential Access • Information is accessed in the order it is stored in the file. • Read sequentially. • Key field uniquely identifies the record & determines storage order • Appended at the end of file • Typically used in batch applications Operating System Concepts

  8. Indexed Sequential File • Adds an index to the file to support random access • Adds an overflow file • Greatly reduces the time required to access a single record • Multiple levels of indexing can be used to provide greater efficiency in access Operating System Concepts

  9. Direct Access Method • Read and Write Randomly • Typically used in Hard Disk rather than magnetic tapes. Operating System Concepts

  10. Directory Structure • A collection of nodes containing information about all files. Directory Files F 1 F 2 F 3 F 4 F n • Both the directory structure and the files reside on disk. • Backups of these two structures are kept on tapes. Operating System Concepts

  11. Information in a Device Directory • Name • Type • Address • Current length • Maximum length • Date last updated (for dump) • Owner ID • Protection information Operating System Concepts

  12. Operations Performed on Directory • Search for a file • Create a file • Delete a file • List a directory • Rename a file • Traverse the file system • Link and Unlink Operating System Concepts

  13. Organize the Directory (Logically) to Obtain • Efficiency – locating a file quickly. • Naming – convenient to users. • Two users can have same name for different files. • The same file can have several different names. • Grouping – logical grouping of files by properties, (e.g., all Pascal programs, all games, …) Operating System Concepts

  14. Single-Level Directory • A single directory for all users. • Naming problem • Grouping problem Operating System Concepts

  15. Two-Level Directory • Separate directory for each user. Operating System Concepts

  16. Tree-Structured Directories Operating System Concepts

  17. Tree-Structured Directories (Cont.) • Absolute or relative path name • Creating a new file is done in current directory. • Delete a file rm <file-name> • Creating a new subdirectory is done in current directory. mkdir <dir-name> Example: if in current directory /spell/mail mkdir count mail prog copy prt exp count • Deleting “mail”  deleting the entire subtree rooted by “mail”. Operating System Concepts

  18. Acyclic-Graph Directories • Have shared subdirectories and files. Operating System Concepts

  19. Protection • File owner/creator should be able to control: • what can be done • by whom • Types of access • Read • Write • Execute • Append • Delete • List Operating System Concepts

  20. Access Lists and Groups • Mode of access: read, write, execute • Three classes of users RWX a) owner access 7  1 1 1 RWX b) groups access 6  1 1 0 RWX c) public access 1  0 0 1 • Ask manager to create a group (unique name), say G, and add some users to the group. • For a particular file (say game) or subdirectory, define an appropriate access. owner group public chmod 761 game • Attach a group to a file • chgrpG game Operating System Concepts

More Related