10文件系统教学.ppt

文件系统 文件系统 为什么需要文件系统 文件和文件系统 文件类型 文件系统模型 文件操作 文件逻辑结构 目录管理 文件共享与保护 File Concept Contiguous logical address space Types: Data numeric character binary Program 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 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. File Operations create write read reposition within file – file seek delete truncate open(Fi) – search the directory structure on disk for entry Fi, and move the content of entry to memory. close (Fi) – move the content of entry Fi in memory to directory structure on disk. File Types – name, extension Access Methods Sequential Access read next write next reset no read after last write (rewrite) Direct Access read n write n position to n read next write next rewrite n n = relative block number Directory Structure A collection of nodes containing information about all files. Information in a Device Directory Name Type Address Current length Maximum length Date last accessed (for archival) Date last updated (for dump) Owner ID (who pays) Protection information (discuss later) Operations Performed on Directory Search for a file Create a file Delete a file List a directory Rename a file Traverse the file system Efficiency – locating a file quickly. Naming – convenient to users. Two users can have same name for different files. The same file can have several differen