Bài giảng gồm có những nội dung chính sau: The security environment, basics of cryptography, user authentication, attacks from inside the system, attacks from outside the system, protection mechanisms, trusted systems. | Chapter 4. FILE Management OBJECTIVES 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 protection 1. File System Interface . File concept A file is a named collection of related information that is recorded on secondary storage. From a user's perspective, a file is the smallest allotment of logical secondary storage Commonly, files represent programs (both source and object forms) and data. In general, a file is a sequence of bits, bytes, lines, or records, the meaning of which is defined by the file's creator and user. File Attributes A file is named, for the convenience of its human users, and is referred to by its name. A file's attributes vary from one operating system to another but typically consist of these: Name–only information kept in human-readable form Identifier–unique tag (number) identifies file within file system 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 File Operations A file is an abstract data type. The basic file operations Creating a file:Two steps are necessary. First, space in the file system must be found for the file. Second, an entry for the new file must be made in the directory. Writing a file: A system call specifying both the name of the file and the information to be written to the file. Given the name of the file, the system searches the directory to find the file's location. Reading a file: A system call that specifies the name of the file and where (in memory) the next block of the file should be put. Repositioning within a file: The directory is searched for the appropriate entry, and the current-file-position pointer | Chapter 4. FILE Management OBJECTIVES 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 protection 1. File System Interface . File concept A file is a named collection of related information that is recorded on secondary storage. From a user's perspective, a file is the smallest allotment of logical secondary storage Commonly, files represent programs (both source and object forms) and data. In general, a file is a sequence of bits, bytes, lines, or records, the meaning of which is defined by the file's creator and user. File Attributes A file is named, for the convenience of its human users, and is referred to by its name. A file's attributes vary from one operating system to another but typically consist of these: Name–only information kept in human-readable form Identifier–unique tag (number) .
