A file handle SM_FileHandle represents an open page file. Besides the file name, the handle store the total number of pages in the file and the current page position. The current page position is used by some of the read and write methods of the storage manager. For example, readCurrentBlock reads the curPagePos=th page counted from the beginning of the file. When opening a file, the current page should be the first page in the file (=curPagePos=0) and the totalNumPages has to be initialized based on the file size. Use the mgmtInfo to store additional information about the file needed by your implementation, e.g., a POSIX file descriptor.

Hint: You should reserve some space in the beginning of a file to store information such as the total number of pages. Hint: Use mgmtInfo to store any bookkeeping info about a file your storage manager needs.

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typedef struct SM_FileHandle {
  char *fileName;
  int totalNumPages;
  int curPagePos;
  void *mgmtInfo;
} SM_FileHandle;

A page handle is an pointer to an area in memory storing the data of a page. Methods that write the data pointed to by a page handle to disk or read a page from disk into the area of memory pointed to by the page handle require that the handle is pointing to an previously allocated block of memory that is at least PAGE_SIZE number of bytes long.

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typedef char* SM_PageHandle;

Create a new page file fileName. The initial file size should be one page. This method should fill this single page with '\0' bytes.

Opens an existing page file. Should return RC_FILE_NOT_FOUND if the file does not exist. The second parameter is an existing file handle. If opening the file is successful, then the fields of this file handle should be initialized with the information about the opened file. For instance, you would have to read the total number of pages that are stored in the file from disk.

Close an open page file or destroy (delete) a page file.

The method reads the block at position pageNum 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.

Return the current page position in a file

Read the first respective last page in a file

Read the current, previous, or next 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.

Write a page to disk using either the current position or an absolute position.

Increase the number of pages in the file by one. The new last page should be filled with zero bytes.

If the file has less than numberOfPages pages then increase the size to numberOfPages.

The header file dberror.h defines several error codes as macros. As you may have noticed the storage manager functions all return an RC value. This value should indicate whether an operation was successful and if not what type of error occurred. If a method call is successful, the function should return RC_OK. The printError function can be used to output an error message based on a return code and the message stored in global variable RC_message (implemented in dberror.c).