static int memdbWrite(sqlite3_file*,const void*,int iAmt, sqlite3_int64 iOfst);
static int memdbTruncate(sqlite3_file*, sqlite3_int64 size);
static int memdbSync(sqlite3_file*, int flags);
static int memdbFileSize(sqlite3_file*, sqlite3_int64 *pSize);
static int memdbLock(sqlite3_file*, int);
static int memdbCheckReservedLock(sqlite3_file*, int *pResOut);
static int memdbFileControl(sqlite3_file*, int op, void *pArg);
static int memdbSectorSize(sqlite3_file*);
static int memdbDeviceCharacteristics(sqlite3_file*);
static int memdbFetch(sqlite3_file*, sqlite3_int64 iOfst, int iAmt, void **pp);
static int memdbUnfetch(sqlite3_file*, sqlite3_int64 iOfst, void *p);

/*
** Methods for MemVfs
*/
................................................................................
  memdbTruncate,                   /* xTruncate */
  memdbSync,                       /* xSync */
  memdbFileSize,                   /* xFileSize */
  memdbLock,                       /* xLock */
  memdbLock,                       /* xUnlock - same as xLock in this case */ 
  memdbCheckReservedLock,          /* xCheckReservedLock */
  memdbFileControl,                /* xFileControl */
  memdbSectorSize,                 /* xSectorSize */
  memdbDeviceCharacteristics,      /* xDeviceCharacteristics */
  0,                               /* xShmMap */
  0,                               /* xShmLock */
  0,                               /* xShmBarrier */
  0,                               /* xShmUnmap */
  memdbFetch,                      /* xFetch */
  memdbUnfetch                     /* xUnfetch */
................................................................................
}

/*
** Try to enlarge the memory allocation to hold at least sz bytes
*/
static int memdbEnlarge(MemFile *p, sqlite3_int64 newSz){
  unsigned char *pNew;
  if( (p->mFlags & SQLITE_DESERIALIZE_RESIZEABLE)==0 ) return SQLITE_FULL;
  if( p->nMmap>0 ) return SQLITE_FULL;

  pNew = sqlite3_realloc64(p->aData, newSz);
  if( pNew==0 ) return SQLITE_FULL;
  p->aData = pNew;
  p->szMax = newSz;
  return SQLITE_OK;
}

/*
** Write data to an memdb-file.
................................................................................
  sqlite3_file *pFile,
  const void *z,
  int iAmt,
  sqlite_int64 iOfst
){
  MemFile *p = (MemFile *)pFile;
  if( iOfst+iAmt>p->sz ){


    if( iOfst+iAmt>p->szMax && memdbEnlarge(p, (iOfst+iAmt)*2) ){

      return SQLITE_FULL;
    }
    if( iOfst>p->sz ) memset(p->aData+p->sz, 0, iOfst-p->sz);
    p->sz = iOfst+iAmt;
  }
  memcpy(p->aData+iOfst, z, iAmt);
  return SQLITE_OK;
}
................................................................................

/*
** Truncate an memdb-file.
*/
static int memdbTruncate(sqlite3_file *pFile, sqlite_int64 size){
  MemFile *p = (MemFile *)pFile;
  if( size>p->sz ){
    if( size>p->szMax && memdbEnlarge(p, size) ) return SQLITE_FULL;



    memset(p->aData+p->sz, 0, size-p->sz);
  }
  p->sz = size; 
  return SQLITE_OK;
}

/*
................................................................................
  if( op==SQLITE_FCNTL_VFSNAME ){
    *(char**)pArg = sqlite3_mprintf("memdb(%p,%lld)", p->aData, p->sz);
    rc = SQLITE_OK;
  }
  return rc;
}


/*
** Return the sector-size in bytes for an memdb-file.
*/
static int memdbSectorSize(sqlite3_file *pFile){
  return 1024;
}


/*
** Return the device characteristic flags supported by an memdb-file.
*/
static int memdbDeviceCharacteristics(sqlite3_file *pFile){
  return SQLITE_IOCAP_ATOMIC | 
         SQLITE_IOCAP_POWERSAFE_OVERWRITE |
................................................................................
  sqlite3_vfs *pVfs,
  const char *zName,
  sqlite3_file *pFile,
  int flags,
  int *pOutFlags
){
  MemFile *p = (MemFile*)pFile;



  memset(p, 0, sizeof(*p));
  if( (flags & SQLITE_OPEN_MAIN_DB)==0 ) return SQLITE_CANTOPEN;
  p->mFlags = SQLITE_DESERIALIZE_RESIZEABLE | SQLITE_DESERIALIZE_FREEONCLOSE;
  *pOutFlags = flags | SQLITE_OPEN_MEMORY;
  p->base.pMethods = &memdb_io_methods;
  return SQLITE_OK;
}

/*
** Delete the file located at zPath. If the dirSync argument is true,
** ensure the file-system modifications are synced to disk before
................................................................................
}

/* 
** This routine is called when the extension is loaded.
** Register the new VFS.
*/
int sqlite3MemdbInit(void){


  memdb_vfs.pAppData = sqlite3_vfs_find(0);

  memdb_vfs.szOsFile = sizeof(MemFile);
  return sqlite3_vfs_register(&memdb_vfs, 0);
}
#endif /* SQLITE_ENABLE_MEMDB */

static int memdbWrite(sqlite3_file*,const void*,int iAmt, sqlite3_int64 iOfst);
static int memdbTruncate(sqlite3_file*, sqlite3_int64 size);
static int memdbSync(sqlite3_file*, int flags);
static int memdbFileSize(sqlite3_file*, sqlite3_int64 *pSize);
static int memdbLock(sqlite3_file*, int);
static int memdbCheckReservedLock(sqlite3_file*, int *pResOut);
static int memdbFileControl(sqlite3_file*, int op, void *pArg);
/* static int memdbSectorSize(sqlite3_file*); // not used */
static int memdbDeviceCharacteristics(sqlite3_file*);
static int memdbFetch(sqlite3_file*, sqlite3_int64 iOfst, int iAmt, void **pp);
static int memdbUnfetch(sqlite3_file*, sqlite3_int64 iOfst, void *p);

/*
** Methods for MemVfs
*/
................................................................................
  memdbTruncate,                   /* xTruncate */
  memdbSync,                       /* xSync */
  memdbFileSize,                   /* xFileSize */
  memdbLock,                       /* xLock */
  memdbLock,                       /* xUnlock - same as xLock in this case */ 
  memdbCheckReservedLock,          /* xCheckReservedLock */
  memdbFileControl,                /* xFileControl */
  0, /* memdbSectorSize,*/         /* xSectorSize */
  memdbDeviceCharacteristics,      /* xDeviceCharacteristics */
  0,                               /* xShmMap */
  0,                               /* xShmLock */
  0,                               /* xShmBarrier */
  0,                               /* xShmUnmap */
  memdbFetch,                      /* xFetch */
  memdbUnfetch                     /* xUnfetch */
................................................................................
}

/*
** Try to enlarge the memory allocation to hold at least sz bytes
*/
static int memdbEnlarge(MemFile *p, sqlite3_int64 newSz){
  unsigned char *pNew;
  if( (p->mFlags & SQLITE_DESERIALIZE_RESIZEABLE)==0 || p->nMmap>0 ){
    return SQLITE_FULL;
  }
  pNew = sqlite3_realloc64(p->aData, newSz);
  if( pNew==0 ) return SQLITE_NOMEM;
  p->aData = pNew;
  p->szMax = newSz;
  return SQLITE_OK;
}

/*
** Write data to an memdb-file.
................................................................................
  sqlite3_file *pFile,
  const void *z,
  int iAmt,
  sqlite_int64 iOfst
){
  MemFile *p = (MemFile *)pFile;
  if( iOfst+iAmt>p->sz ){
    int rc;
    if( iOfst+iAmt>p->szMax
     && (rc = memdbEnlarge(p, (iOfst+iAmt)*2))!=SQLITE_OK
    ){
      return rc;
    }
    if( iOfst>p->sz ) memset(p->aData+p->sz, 0, iOfst-p->sz);
    p->sz = iOfst+iAmt;
  }
  memcpy(p->aData+iOfst, z, iAmt);
  return SQLITE_OK;
}
................................................................................

/*
** Truncate an memdb-file.
*/
static int memdbTruncate(sqlite3_file *pFile, sqlite_int64 size){
  MemFile *p = (MemFile *)pFile;
  if( size>p->sz ){
    int rc;
    if( size>p->szMax && (rc = memdbEnlarge(p, size))!=SQLITE_OK ){
      return rc;
    }
    memset(p->aData+p->sz, 0, size-p->sz);
  }
  p->sz = size; 
  return SQLITE_OK;
}

/*
................................................................................
  if( op==SQLITE_FCNTL_VFSNAME ){
    *(char**)pArg = sqlite3_mprintf("memdb(%p,%lld)", p->aData, p->sz);
    rc = SQLITE_OK;
  }
  return rc;
}

#if 0  /* Not used because of SQLITE_IOCAP_POWERSAFE_OVERWRITE */
/*
** Return the sector-size in bytes for an memdb-file.
*/
static int memdbSectorSize(sqlite3_file *pFile){
  return 1024;
}
#endif

/*
** Return the device characteristic flags supported by an memdb-file.
*/
static int memdbDeviceCharacteristics(sqlite3_file *pFile){
  return SQLITE_IOCAP_ATOMIC | 
         SQLITE_IOCAP_POWERSAFE_OVERWRITE |
................................................................................
  sqlite3_vfs *pVfs,
  const char *zName,
  sqlite3_file *pFile,
  int flags,
  int *pOutFlags
){
  MemFile *p = (MemFile*)pFile;
  if( (flags & SQLITE_OPEN_MAIN_DB)==0 ){
    return ORIGVFS(pVfs)->xOpen(ORIGVFS(pVfs), zName, pFile, flags, pOutFlags);
  }
  memset(p, 0, sizeof(*p));

  p->mFlags = SQLITE_DESERIALIZE_RESIZEABLE | SQLITE_DESERIALIZE_FREEONCLOSE;
  if( pOutFlags ) *pOutFlags = flags | SQLITE_OPEN_MEMORY;
  p->base.pMethods = &memdb_io_methods;
  return SQLITE_OK;
}

/*
** Delete the file located at zPath. If the dirSync argument is true,
** ensure the file-system modifications are synced to disk before
................................................................................
}

/* 
** This routine is called when the extension is loaded.
** Register the new VFS.
*/
int sqlite3MemdbInit(void){
  sqlite3_vfs *pLower = sqlite3_vfs_find(0);
  int sz = pLower->szOsFile;
  memdb_vfs.pAppData = pLower;
  if( sz<sizeof(MemFile) ) sz = sizeof(MemFile);
  memdb_vfs.szOsFile = sz;
  return sqlite3_vfs_register(&memdb_vfs, 0);
}
#endif /* SQLITE_ENABLE_MEMDB */