Bir dosya sistemi tasarımı ve gerçekleştirilmesi

Abstract

Bu çalışmanın amacı, Dosya Sistemi kavramını, işletim sistemini oluşturan çekirdek içindeki yeri ve işlevleri acısından incelemektir. Bununla birlikte genel anlamda birkaç Dosya Sistemi yapısı incelenmiş, sentez olarak ortaya çıkan ve bilgisayar üzerinde çalışan bir Dosya Sistemi tasarlanmıştır. Birici bölüm, kanunun giriş bölümü olup kullanıcı ile Dosya Sistemi arasındaki bağa değinmektedir. İkici bölüm, genel anlamda bilgisayar donanımı ve işletim sistemi kavramları üzerinde durmaktadır. üçüncü bölüm, çekirdek yapısı ile bu yapı içersinde Dosya Sisteminin yeri ve yaratmış olduğumuz Dosya Sistemine geçişi aktarmaktadır. Dördüncü bölümde, oluşturulan Dosya Sistemi ayrıntılı olarak bir örnek üzerinde ele alınmış olup, geliştirilen Dosya Sistemi komutları açıklanmaktadır. Besinci bölüm, Dosya Sisteminde gecen ve kullanıcıya aktarılan hata mesajları konusuna değinmektedir. Altıncı Bölüm, Dosya Sisteminde kullanılmış olan disk türüne ilişkin teknik bilgileri içermektedir. Dosya Sisteminin bilgisayar uygulaması, "C" programlama dili ve "Embedded" türü bir disk ile gerçek leşti ri İm istir.

In-formation management is concerned with the storage and retrieval o-F in-Formation entrusted to the system in much the same manner as a library. The following are the basic -functions of information management. 1) Keeping track of all information in the system through various tables, the major one being the file directory - sometimes called Volume Table of Contents (VTOC). These tables contain the name, location and accessing rights of all information within the system. 2) Deciding policy for determining where and how information is stored and who gets access to the in-Formation. Factors influencing this policy are efficient utilization of secondary storage, efficient access, flexibility to users, and protection of access rights to the information requested. 3) Allocating the information resource. Once the decision is made to let a process have access to in-formation, the allocation modules must find the desired information, make the desired information accessible to the process, and establish the appropriate access rights. 4) Deallocating of the information resource. Once the information is no longer needed, temporary table entries and other such resources may be released. If the user has updated the information, the original copy of that information may be updated for possible use by other processes. The modules of information management are sometimes collectively referred to as the file system. Such a work was first presented by Madnick (1969) and is a framework for implementing a file system. VI Each level of the -file system are as -follows 1) Symbolic File System 2) Basic File System 3) Protection 4) Logical File System 5) Physical File System 6) Device Strategies The -File system is intended to provide convenient management o-F both permanent (long term) and temporary (short term) information. The programmer is freed from problems such as the allocation of space for his information, physical storage formats, and I/O accesing. One goal of a file system is to allow the programmer to concern himself only with the logical structure of operations performed in processing his information. Shortly a file system is concerned with the logical organization of information. simple So as to keep track of files, the file system normally provides "directories". A "directory" typically contains a number of entries. The entries may contain information about the file as shown in fig.l. Directory File File File File File Next Next name size type entry_no father file dir File pointers File current Sector number Creation time Time of last modification Fig. 1 vii A file, which is called VTOC, contains all these kind of information and each time, when power gets on this -File is red by the system. And also all entries keep place in FAT. The file named FAT, points to a certain place on the disc. There are two methods -For -Finding -free storage onto the disc. One o-F them is linked lists and the other is bit maps. Our file system uses linked lists. In addition to this, the structure of our file system accepts commands from the user. When a command arrives, its type is extracted and a related subroutine is executed. After termi nati tion of that sub procedure, a messages is send to the user and the main program goes back to the top of the loop to wait for another command. Another subject, files are normally stored on disc, so management of disc space is a major concern to file system designers. Two general strategies are passible for storing an " n" byte file : - "n" consecutive bytes of disc space are allocated. - The second strategy is to split the file up into a number of (not necessaryly) contiguous blacks. Storing a file as contiguous sequence of bytes has the obvious problem that if a file grows, which is a very common occurence, it will probably have to be moved on the disc. For this reason, nearly all file systems chop files up into fixed-size blocks that need not to be adjacent. And also our file system was constructed in this manner. But the major problem was that how big the block should be. The sector, the cylinder and the head are obvious candidates for the unit of allocation. Out disk type is "Embedded" and one sector is 512 bytes. Because in our file system, the maximum number of files that can be created is 200, so we can divide the total capacity of disc into 200 equal pieces. This is an interesting point because naturally a block size of 512 bytes will increase. So file system will handle four sectors as one part and will always read or write four consecutive sectors. viii In our -File system, -Four sectors are called as "cluster". There is always an upper and lower bound -For each cluster. Between these bounds sectors on disc are consecutive. When it comes to the end o-F a cluster, another entry number is taken -From FAT ( File Allocation Table ). And this procedure goes on until the end o-F -File mark is -Found on the disc. Associated with each disc there is a table called "FILE ALLOCATION TABLE". This table contains an entry -For each disc block. The directory entry -For each -File gives the block number o-F the -First block o-F the -File. That slot in the FAT contains the block number o-F the next block. All the commands have a certain syntax. Be-Fore the command is executed, the -File system so-Ftware checks the syntax. I-F a syntax error occures a certain message is displayed on the screen, command execution is aborted and the program waits -For -Further entries. The implemented commands are listed below. - Creating a -File. - Modi-Ficating a created -File. - Reading a -File. - Change working directory. - Changing or assigning new attributes, such as reading, writing and executing. - Searching in the whole -File system -For a given -Fi le/directory. - Listing -Files/directories o-F the working directory. - Printing the path o-F the working directory. - Cleaning the Screen. - Inquiring the number o-F -Free or used blocks on the disc. - Listing the contents o-F the File Allocation Table - Changing the name o-F a -File/directory - Moving the -File to a given directory path. - Deleting -Files, but these -Files are not directly deleted, instead they are stored as hidden files. ix - Displaying hidden -files. - Erasing hidden -Files which are deleted be-Fore. - Undelete deleted -Files. I-F the user deletes the -file he has the possibility to undelete it. - Exit o-F the -File system. Shortly this application consist o-F a simple and basic -file system design. It is possible to develop it -Further and add new commands.