The program is an attempt to implement a simple file system that allows managing files and directories in a virtual in-memory disk. The file system is based on simplified concepts of a File Allocation Table (FAT). It allows the creation of files and directories within this virtual hard disk and the performance of simple read-and-write operations on files.
The virtual disk is simulated by an array of memory blocks, where each block is a fixed array of bytes. Each block has a block number (from 0 to MAXBLOCKS-1). The allocation of a new block to a file is recorded in the FAT. The FAT is a table (an array of integers) of size MAXBLOCKS that acts as a kind of block directory for the complete disk content: it contains an entry for each block and records whether this block is allocated to a file or unused. The FAT itself is also stored on this virtual disk at a particular location.
The complete public interface of the file system for this virtual disk is the following:
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void format() - Creates the initial structure on the virtual disk, writing the FAT and the root directory into the virtual disk
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MyFILE * myfopen ( const char * filename, const char * mode ) - Opens a file on the virtual disk and manages a buffer for it of size BLOCKSIZE, mode may be either “r” for read-only or “w” for read/write/append (default “w”)
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void myfclose ( MyFILE * stream ) - Closes the file, writes out any blocks not written to disk
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int myfgetc ( MyFILE * stream ) - Returns the next byte of the open file, or EOF (== -1)
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void myfputc ( int b, MyFILE * stream ) - Writes a byte to the file. Depending on the write policy, either writes the disk block containing the written byte to disk, or waits until block is full
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void mymkdir ( const char * path ) - The function creates a new directory, using path, e.g. mymkdir(“/first/second/third”) creates directory “third” in parent dir “second”, which is a subdir of directory “first”, and “first is a sub directory of the root directory
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char ** mylistdir (const char * path) - Lists the content of a directory and returns a list of strings, where the last element is NULL
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void mychdir ( const char * path ) - The function changes the current directory into an existing directory, using path, e.g. mkdir (“/first/second/third”) creates directory “third” in parent dir “second”, which is a subdir of directory “first”, and “first is a sub directory of the root directory
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void myremove ( const char * path ) - Removes an existing file, using path, e.g. myremove (“/first/second/third/testfile.txt”)
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void myrmdir ( const char * path ) - Removes an existing directory, using path, e.g. myrmdir “/first/second/third”) removes directory “third” in parent dir “second”, which is a subdir of directory “first”, and “first is a sub directory of the root directory
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int nextUnusedBlock () - Returns the next unused block number
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int nextUnusedDir () - Returns the next unused directory entry number
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int fileLocation ( const char* filename ) - Looks for a file block given a path (file name)
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void cleanFAT ( int fatEntry ) - Recursively cleans FAT by setting its entries to UNUSED
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diskblock_t freeDirBlock () - Returns a newly created free directory block
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int fileEntryIndex (const char *path) - Checks if there is an entry that matches the path. If so returns the entry number and EOF otherwise
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int isDirEmpty (dirblock_t dir) - Checks whether an entry is empty (unused). Returns TRUE if it finds such entry and FALSE otherwise
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void printContents (char **contentList) - Prints the contents of a list (in our case files and folder names)
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void myfvdsys(const char* sysFile, const char* vdFile) - Copies the contents of a virtual disk file to a physical disk file
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void myfsysvd(const char* sysFile, const char* vdFile) - Copies the contents of a physical disk file to virtual disk file
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void myfcopy (char* src, char* dst) - Copies content from source to destination file (in the virtual disk)
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void myfmove (char* src, char* dst) - Moves content from source to destination file (in the virtual disk) and deletes source file (reuses “myfcopy” and “myremove” functions)
(!) Before you start make sure u have all the files required in the same directory: filesys.c, filesys.h, shell.c and Makefile.
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You will need to install C compiler if you don’t have one, such as GCC (https://gcc.gnu.org/). If you are on a Windows computer, you can run the command ‘gcc -v’ to check if it’s already installed.
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Open the command prompt by going to the Start button and typing ‘cmd' in the search or run bar (or click on Command Prompt if provided).
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Change your directory to where you have your C program (in our casefilesys.c, filesys.h, shell.c and Makefile.) using the command ‘cd’. We need to pass the name of the directory in which the program is stored. o Example: cd Desktop (if the program is already in the user directory)
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Compile the source code by typing ‘make’ in the Command Prompt (compilation is automatically done by the Makefile). (additional command ‘make clean’ to clean up the compilation files)
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Run the executable file by typing the name of the executable file without the extension (in our case ‘shell’) and hit ‘Enter’.
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Open the terminal window.
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If you don’t have a compiler already installed you will need to run the following apt-get commands in the terminal to install GNU c/c++ compiler:
$ sudo apt-get update $ sudo apt-get install build-essential manpages-dev -
Navigate to the program directory using the command ‘cd’ and type in ‘make' to compile the program (since we have a Makefile). (additional command ‘make clean’ to clean up the compilation files)
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To run the executable just type in ‘./’ (‘./shell’ in our case) and hit ‘Enter’.
$ gcc -c filesys.c
$ gcc -c shell.c
$ gcc -o shell shell.o filesys.o