SQLite

static int memdbClose(sqlite3_file*);
static int memdbRead(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
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);// not used */
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
*/
static int memdbOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
/* static int memdbDelete(sqlite3_vfs*, const char *zName, int syncDir); */
static int memdbAccess(sqlite3_vfs*, const char *zName, int flags, int *);
static int memdbFullPathname(sqlite3_vfs*, const char *zName, int, char *zOut);
static void *memdbDlOpen(sqlite3_vfs*, const char *zFilename);
static void memdbDlError(sqlite3_vfs*, int nByte, char *zErrMsg);
static void (*memdbDlSym(sqlite3_vfs *pVfs, void *p, const char*zSym))(void);
static void memdbDlClose(sqlite3_vfs*, void*);
static int memdbRandomness(sqlite3_vfs*, int nByte, char *zOut);
static int memdbSleep(sqlite3_vfs*, int microseconds);
/* static int memdbCurrentTime(sqlite3_vfs*, double*); */
static int memdbGetLastError(sqlite3_vfs*, int, char *);
static int memdbCurrentTimeInt64(sqlite3_vfs*, sqlite3_int64*);

static sqlite3_vfs memdb_vfs = {
  2,                           /* iVersion */
  0,                           /* szOsFile (set when registered) */
  1024,                        /* mxPathname */
  0,                           /* pNext */
  "memdb",                     /* zName */
  0,                           /* pAppData (set when registered) */ 
  memdbOpen,                   /* xOpen */
  0, /* memdbDelete, */        /* xDelete */
  memdbAccess,                 /* xAccess */
  memdbFullPathname,           /* xFullPathname */
  memdbDlOpen,                 /* xDlOpen */
  memdbDlError,                /* xDlError */
  memdbDlSym,                  /* xDlSym */
  memdbDlClose,                /* xDlClose */
  memdbRandomness,             /* xRandomness */
  memdbSleep,                  /* xSleep */
  0, /* memdbCurrentTime, */   /* xCurrentTime */
  memdbGetLastError,           /* xGetLastError */
  memdbCurrentTimeInt64        /* xCurrentTimeInt64 */
};

static const sqlite3_io_methods memdb_io_methods = {
  3,                              /* iVersion */
  memdbClose,                      /* xClose */
  memdbRead,                       /* xRead */
  memdbWrite,                      /* xWrite */
  memdbTruncate,                   /* xTruncate */
  memdbSync,                       /* xSync */
  memdbFileSize,                   /* xFileSize */
  memdbLock,                       /* xLock */
  memdbLock,                       /* xUnlock - same as xLock in this case */ 
  0, /* memdbCheckReservedLock, */ /* xCheckReservedLock */
  memdbFileControl,                /* xFileControl */
  0, /* memdbSectorSize,*/         /* xSectorSize */
  memdbDeviceCharacteristics,      /* xDeviceCharacteristics */
  0,                               /* xShmMap */
  0,                               /* xShmLock */
  0,                               /* xShmBarrier */
  0,                               /* xShmUnmap */

  }
  memcpy(p->aData+iOfst, z, iAmt);
  return SQLITE_OK;
}

/*
** Truncate an memdb-file.
**
** In rollback mode (which is always the case for memdb, as it does not
** support WAL mode) the truncate() method is only used to reduce
** the size of a file, never to increase the size.
*/
static int memdbTruncate(sqlite3_file *pFile, sqlite_int64 size){
  MemFile *p = (MemFile *)pFile;
  if( NEVER(size>p->sz) ) return SQLITE_FULL;






  p->sz = size; 
  return SQLITE_OK;
}

/*
** Sync an memdb-file.
*/

*/
static int memdbLock(sqlite3_file *pFile, int eLock){
  MemFile *p = (MemFile *)pFile;
  p->eLock = eLock;
  return SQLITE_OK;
}

#if 0 /* Never used because memdbAccess() always returns false */
/*
** Check if another file-handle holds a RESERVED lock on an memdb-file.
*/
static int memdbCheckReservedLock(sqlite3_file *pFile, int *pResOut){
  *pResOut = 0;
  return SQLITE_OK;
}
#endif

/*
** File control method. For custom operations on an memdb-file.
*/
static int memdbFileControl(sqlite3_file *pFile, int op, void *pArg){
  MemFile *p = (MemFile *)pFile;
  int rc = SQLITE_NOTFOUND;

){
  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;
  assert( pOutFlags!=0 );  /* True because flags==SQLITE_OPEN_MAIN_DB */
  *pOutFlags = flags | SQLITE_OPEN_MEMORY;
  p->base.pMethods = &memdb_io_methods;
  return SQLITE_OK;
}

#if 0 /* Only used to delete rollback journals, master journals, and WAL
      ** files, none of which exist in memdb.  So this routine is never used */
/*
** Delete the file located at zPath. If the dirSync argument is true,
** ensure the file-system modifications are synced to disk before
** returning.
*/
static int memdbDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
  return SQLITE_IOERR_DELETE;
}
#endif

/*
** Test for access permissions. Return true if the requested permission
** is available, or false otherwise.
**
** With memdb, no files ever exist on disk.  So always return false.
*/
static int memdbAccess(
  sqlite3_vfs *pVfs, 
  const char *zPath, 
  int flags, 
  int *pResOut
){

** Sleep for nMicro microseconds. Return the number of microseconds 
** actually slept.
*/
static int memdbSleep(sqlite3_vfs *pVfs, int nMicro){
  return ORIGVFS(pVfs)->xSleep(ORIGVFS(pVfs), nMicro);
}

#if 0  /* Never used.  Modern cores only call xCurrentTimeInt64() */
/*
** Return the current time as a Julian Day number in *pTimeOut.
*/
static int memdbCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
  return ORIGVFS(pVfs)->xCurrentTime(ORIGVFS(pVfs), pTimeOut);
}
#endif

static int memdbGetLastError(sqlite3_vfs *pVfs, int a, char *b){
  return ORIGVFS(pVfs)->xGetLastError(ORIGVFS(pVfs), a, b);
}
static int memdbCurrentTimeInt64(sqlite3_vfs *pVfs, sqlite3_int64 *p){
  return ORIGVFS(pVfs)->xCurrentTimeInt64(ORIGVFS(pVfs), p);
}

  rc = sqlite3_step(pStmt);
  db->init.reopenMemdb = 0;
  if( rc!=SQLITE_DONE ){
    rc = SQLITE_ERROR;
    goto end_deserialize;
  }
  p = memdbFromDbSchema(db, zSchema);
  /* The memdbFromDbSchema() call can only fail if zSchema is not
  ** a valid schema name or if the schema is not a memdb schema.  But
  ** neither of those things can be true here, so failure is not possible */
  assert( p!=0 );


  p->aData = pData;
  p->sz = szDb;
  p->szMax = szBuf;
  p->mFlags = mFlags;
  rc = SQLITE_OK;

end_deserialize:
  sqlite3_finalize(pStmt);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

/*