File System Implementation-R.D.Sivakumar
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This document discusses several key data structures used in file system implementation: 1) A boot-control block and file control block (FCB) store metadata like ownership and permissions. 2) A directory structure stores file names and pointers to FCBs. 3) A volume control block stores partition information and pointers to free blocks. 4) In-memory tables track open files and recently accessed directories.
File System Implementation-R.D.Sivakumar
- 1. Video Lecture and E-Content Created by R.D.SIVAKUMAR,M.Sc.,M.Phil.,M.Tech., Assistant Professor of Computer Science & Assistant Professor and Head, Department of M.Com.(CA), Ayya Nadar Janaki Ammal College, Sivakasi – 626 124. Mobile: 099440-42243 e-mail : sivamsccsit@gmail.com website: www.rdsivakumar.blogspot.in FILE SYSTEM IMPLEMENTATION
- 2. File systems store several important data structures on the disk: A boot-control block - The boot block in UNIX or the partition boot sector in Windows contains information about how to boot the system off of this disk. The File Control Block - It containing details about ownership, size, permissions, dates, etc. OVERVIEW
- 3. A directory structure - It containing file names and pointers to corresponding FCBs. A volume control block - The master file table in UNIX or the super block in Windows, which contains information such as the partition table, number of blocks on each file system, and pointers to free blocks and free FCB blocks.
- 4. An in-memory mount table. An in-memory directory cache of recently accessed directory information. A system-wide open file table, containing a copy of the FCB for every currently open file in the system, as well as some other related information. A per-process open file table, containing a pointer to the system open file table as well as some other information. SEVERAL KEY DATA STRUCTURES STORED IN MEMORY:
- 5. When a new file is created, a new FCB is allocated and filled out with important information regarding the new file. The appropriate directory is modified with the new file name and FCB information. When a file is accessed during a program, the open( ) system call reads in the FCB information from disk, and stores it in the system-wide open file table. FILE SYSTEM COMPONENTS
- 6. If another process already has a file open when a new request comes in for the same file, and it is sharable, then a counter in the system- wide table is incremented and the per-process table is adjusted to point to the existing entry in the system-wide table. When a file is closed, the per-process table entry is freed, and the counter in the system-wide table is decremented. FILE SYSTEM COMPONENTS (Conti..)
- 7. Physical disks are commonly divided into smaller units called partitions. Partitions can either be used as raw devices. The boot block is accessed as part of a raw partition, by the boot program prior to any operating system being loaded. The root partition contains the OS kernel and at least the key portions of the OS needed to complete the boot process. Continuing with the boot process, additional file systems get mounted, adding their information into the appropriate mount table structure. PARTITIONS AND MOUNTING
- 8. Virtual File Systems, VFS, provide a common interface to multiple different file system types. In addition, it provides for a unique identifier (vnode) for files across the entire space, including across all filesystems of different types VIRTUAL FILE SYSTEMS
- 9. The inode object, representing an individual file The file object, representing an open file. The superblock object, representing a file system. The dentry object, representing a directory entry. VIRTUAL FILE SYSTEMS OBJECT TYPES