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Organization of the file system

Customary use of system functions, read and write provides consistent access to the file, but the process could use a challenge system functions lseek to indicate places in the file, which will be O, and the implementation of random file access. Syntax system call functions: position = lseek (fd, offset, reference); where fd-file descriptor that identifies the file-shift offset in bytes, and the reference points, meaning there is a shifting of offset from the beginning of the file, the offset from the current position of I / O or deflection of the end of the file. The return value, position, is the offset in bytes to the place where the operation will begin next read or write. Modern architecture file systems Modern OS provide the user with the opportunity to work directly with multiple file systems (Linux works with Ext2fs, FAT, etc.). File system in the traditional sense becomes part of a broader multi-layer structure (see Fig. 12.12). On the upper level, where is the so-called controller file systems (for example, in Windows 95, this component is called installable filesystem manager). It connects requests for a specific application file system. Each file system (sometimes say filesystem driver) for the initialization phase of the registered manager, telling him entry point for subsequent hits to the file system. The same idea support multiple file systems under one operating system may be implemented differently, for example, based on the concept of a virtual file system. Virtual File System (vfs) is an independent realization of the level and relies on real file systems (s5fs, ufs, FAT, NFS, FFS, Ext2fs). This raises the structure of the virtual file system, a type of virtual nodes vnode index, which synthesizes the index nodes specific systems.
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