SQLite

/*
** 2007 August 22
** 2008 October 7
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains code use to implement an in-memory rollback journal.
** The in-memory rollback journal is used to journal transactions for
** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
**
** @(#) $Id: memjournal.c,v 1.1 2008/10/17 19:13:05 danielk1977 Exp $
** @(#) $Id: memjournal.c,v 1.2 2008/10/28 18:12:36 drh Exp $
*/


#include "sqliteInt.h"

/* Forward references to internal structures */
typedef struct MemJournal MemJournal;
typedef struct FilePoint FilePoint;
typedef struct FileChunk FileChunk;

/* Space to hold the rollback journal is allocated in increments of
** this many bytes.
*/
#define JOURNAL_CHUNKSIZE 1024

/* Macro to find the minimum of two numeric values.
*/
#define MIN(x,y) ((x)<(y)?(x):(y))

/*
** The rollback journal is composed of a linked list of these structures.
*/
struct FileChunk {
  FileChunk *pNext;
  u8 zChunk[JOURNAL_CHUNKSIZE];
  FileChunk *pNext;               /* Next chunk in the journal */
  u8 zChunk[JOURNAL_CHUNKSIZE];   /* Content of this chunk */
};

/*
** An instance of this object serves as a cursor into the rollback journal.
** The cursor can be either for reading or writing.
*/
struct FilePoint {
  sqlite3_int64 iOffset;
  FileChunk *pChunk;
  sqlite3_int64 iOffset;          /* Offset from the beginning of the file */
  FileChunk *pChunk;              /* Specific chunk into which cursor points */
};

/*
** This subclass is a subclass of sqlite3_file.  Each open memory-journal
** is an instance of this class.
*/
struct MemJournal {
  sqlite3_io_methods *pMethod;    /* I/O methods on journal files */
  sqlite3_io_methods *pMethod;    /* Parent class. MUST BE FIRST */
  FileChunk *pFirst;              /* Head of in-memory chunk-list */
  FilePoint endpoint;             /* Pointer to the end of the file */
  FilePoint readpoint;            /* Pointer to the end of the last xRead() */
};

/*
** Read data from the file.

/* 
** Return the number of bytes required to store a MemJournal that uses vfs
** pVfs to create the underlying on-disk files.
*/
int sqlite3MemJournalSize(){
  return sizeof(MemJournal);
}