storage_mgr.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

#include "storage_mgr.h"
#include "dberror.h"

/* manipulating page files */

FILE *file;//Global file variable used by all functions
int blockTobeRead;// Global varaible to store page number, to be used by all Read functions

//This functions intializes the Storage Manager. Returns void
void initStorageManager(void){

}

//This creates a pagefile and intializes a memory allocation using calloc
RC createPageFile (char *fileName) {

    file=fopen(fileName,"w");
	char *pointer=(char *)calloc(PAGE_SIZE,sizeof(char));//reserving the space of PAGE_SIZE
	fwrite(pointer,PAGE_SIZE,sizeof(char),file); //writing to the file
	fclose(file);
	free(pointer);
	return RC_OK;

}

//Opens an existing page file,fields of this file handle should be initialized with the information about the opened file.
RC openPageFile (char *fileName, SM_FileHandle *fHandle) {
    int fileSize,filePageCount;
	FILE *file;		
	//if file cannot be opened or its not exist
	if(!(file=fopen(fileName,"r"))){
		RC_message="Desired file doesn't exist";
		return RC_FILE_NOT_FOUND;
	}else{
	//opening a file in read mode and populating the fHandle structure with important information.
	file=fopen(fileName,"r");
	fHandle->mgmtInfo=file;
	fHandle->fileName=fileName;
	fHandle->curPagePos=0;
	fseek(file,0,SEEK_END);//seeking throgh end of file.
	fileSize=ftell(file);
	//counting number of pages in file.
	filePageCount=fileSize/PAGE_SIZE;
	fHandle->totalNumPages=filePageCount;
	return RC_OK;
	}		
}


//Close an open page file
RC closePageFile (SM_FileHandle *fHandle){
    fHandle=NULL;
	if(file!=NULL){
	fclose(file);
	file=NULL;
	}	
	free(file);
	return RC_OK;

}
//This function destroys a file. It first checks if the file exists.
RC destroyPageFile (char *fileName){
    remove(fileName);
		return RC_OK;

}

RC readBlock (int pageNum, SM_FileHandle *fHandle, SM_PageHandle memPage) {//A page handle is an pointer to an area in memory storing the data of a page
//The method reads the pageNumth block from a file and stores its content in the memory pointed to by the memPage page handle. If the file has less than pageNum pages, the method should return RC_READ_NON_EXISTING_PAGE.
	if(fHandle!=NULL){
			int success;
			//checking the desired page to be read is within limit of totalNumPages also checks numPage should be more than 0
			if(((pageNum)<=(fHandle->totalNumPages)) && (pageNum)>=0){
					success=fseek(fHandle->mgmtInfo,(((pageNum+1)*PAGE_SIZE)),SEEK_SET);//seek to desired position to be read
					fread(memPage,sizeof(char),PAGE_SIZE,fHandle->mgmtInfo);// Reading from file and writing data to memory
					fHandle->curPagePos=pageNum;//setting the current page position file pointer			
					return RC_OK;
			}
			else{
					RC_message="Page to be read doesn't exist in file";
					return RC_READ_NON_EXISTING_PAGE;
				}
		}else{
			RC_message="desired file related data is not initialized";
			return RC_FILE_HANDLE_NOT_INIT;
		}

}



int getBlockPos (SM_FileHandle *fHandle) {
//Return the current page position in a file
	return fHandle->curPagePos;
}

RC readFirstBlock (SM_FileHandle *fHandle, SM_PageHandle memPage) {

//Read the first respective last page in a file
	return readBlock(0,fHandle,memPage);

}

//Read the previous page relative to the curPagePos of the file. The curPagePos should be moved to the page that was read. If the user tries to read a block before the first page of after the last page of the file, the method should return RC_READ_NON_EXISTING_PAGE
RC readPreviousBlock (SM_FileHandle *fHandle, SM_PageHandle memPage) {

	return readBlock(fHandle->curPagePos-1,fHandle,memPage);

}

// readCurrentBlock reads the curPagePosth page counted from the beginning of the file.
RC readCurrentBlock (SM_FileHandle *fHandle, SM_PageHandle memPage){

	return readBlock(fHandle->curPagePos, fHandle,memPage);
}

//Read the next page relative to the curPagePos of the file
RC readNextBlock (SM_FileHandle *fHandle, SM_PageHandle memPage){

	return readBlock(fHandle->curPagePos+1,fHandle,memPage);

}

//Read the first respective last page in a file
RC readLastBlock (SM_FileHandle *fHandle, SM_PageHandle memPage){

	return readBlock(fHandle->totalNumPages,fHandle,memPage);

}

RC writeBlock (int pageNum, SM_FileHandle *fHandle, SM_PageHandle memPage) {
if(fHandle!=NULL){
			if(((pageNum)<=(fHandle->totalNumPages))&&(pageNum)>=0){
					fseek(fHandle->mgmtInfo,(((pageNum+1)*PAGE_SIZE)),SEEK_SET);//seek to position to be written
					fwrite(memPage,sizeof(char),PAGE_SIZE,fHandle->mgmtInfo);//writing to file from memory
					fHandle->curPagePos=pageNum;//updating current page file pointer
					return RC_OK;			
			}
	}else{
			RC_message="desired file related data is not initialized";
			return RC_FILE_HANDLE_NOT_INIT;
		 }
}

RC writeCurrentBlock (SM_FileHandle *fHandle, SM_PageHandle memPage){
////Write a page to disk using either the current position or an absolute position.
	int pos;
	pos = getBlockPos(fHandle);
	RC flag;
	flag = writeBlock(pos, fHandle, memPage);
	return flag;
}

RC appendEmptyBlock (SM_FileHandle *fHandle) {
//Increase the number of pages in the file by one. The new last page should be filled with zero bytes.
	int totalBytes;
		FILE *file;
		if(fHandle!=NULL){
			file=fopen(fHandle->fileName,"a");//opening a file in append mode
			fHandle->totalNumPages+=1;//updating total number of pages in file
			fseek(file,(((fHandle->totalNumPages+1)*PAGE_SIZE)),SEEK_END);//seek to end of file for append operation
			char *pointer=(char *)calloc(PAGE_SIZE,sizeof(char));
			fwrite(pointer,PAGE_SIZE,sizeof(char),file);//writing an empty block to file
			//fHandle->curPagePos=fHandle->totalNumPages;//updating current block page pointer of file
			free(pointer);//freeing the occupied memory
			fclose(file);//closing of file
			return RC_OK;
		}else{
			RC_message="desired file related data is not initialized";
			return RC_FILE_HANDLE_NOT_INIT;
		}
}

RC ensureCapacity(int numOfPages, SM_FileHandle *fHandle) {
//If the file has less than numberOfPages pages then increase the size to numberOfPages.
	int diff,i;
		if(fHandle!=NULL){
			if((fHandle->totalNumPages)<numOfPages){
				diff=numOfPages-(fHandle->totalNumPages);
				for(i=0;i<diff;i++){
					appendEmptyBlock(fHandle);
				}
				return RC_OK;
			}else{
				return RC_OK;
			}	
		}else{
			RC_message="desired file related data is not initialized";
			return RC_FILE_HANDLE_NOT_INIT;
		}
}