SQLite

           && sqlite3_stricmp(azArg[1], "page_size")==0 ){
      /* Do not allow page size changes on a checksum database */
      return SQLITE_OK;
    }
  }else if( op==SQLITE_FCNTL_CKPT_START || op==SQLITE_FCNTL_CKPT_DONE ){
    p->inCkpt = op==SQLITE_FCNTL_CKPT_START;
    if( p->pPartner ) p->pPartner->inCkpt = p->inCkpt;
  }else if( op==SQLITE_FCNTL_CKSM_FILE ){
    /* This VFS needs to obtain a pointer to the corresponding database
    ** file handle from within xOpen() calls to open wal files. To do this,
    ** it uses the sqlite3_database_file_object() API to obtain a pointer
    ** to the file-handle used by SQLite to access the db file. This is
    ** fine if cksmvfs happens to be the top-level VFS, but not if there
    ** are one or more wrapper VFS. To handle this case, this file-control
    ** is used to extract the cksmvfs file-handle from any wrapper file 
    ** handle.  */
    sqlite3_file **ppFile = (sqlite3_file**)pArg;
    *ppFile = (sqlite3_file*)p;
    return SQLITE_OK;
  }
  rc = pFile->pMethods->xFileControl(pFile, op, pArg);
  if( rc==SQLITE_OK && op==SQLITE_FCNTL_VFSNAME ){
    *(char**)pArg = sqlite3_mprintf("cksm/%z", *(char**)pArg);
  }
  return rc;
}

  memset(p, 0, sizeof(*p));
  pSubFile = ORIGFILE(pFile);
  pFile->pMethods = &cksm_io_methods;
  rc = pSubVfs->xOpen(pSubVfs, zName, pSubFile, flags, pOutFlags);
  if( rc ) goto cksm_open_done;
  if( flags & SQLITE_OPEN_WAL ){
    sqlite3_file *pDb = sqlite3_database_file_object(zName);
    rc = pDb->pMethods->xFileControl(pDb, SQLITE_FCNTL_CKSM_FILE, (void*)&pDb);
    assert( rc==SQLITE_OK );
    p->pPartner = (CksmFile*)pDb;
    assert( p->pPartner->pPartner==0 );
    p->pPartner->pPartner = p;
    p->isWal = 1;
    p->computeCksm = p->pPartner->computeCksm;
  }else{
    p->isWal = 0;

foreach {tn3 create_vfs destroy_vfs} {
  1 {} {}
  2 {
    sqlite3rbu_create_vfs -default myrbu ""
  } {
    sqlite3rbu_destroy_vfs myrbu
  }
  3 {
    sqlite3_register_cksumvfs
  } {
    sqlite3_unregister_cksumvfs
  }
} {

  eval $create_vfs

  foreach {tn2 cmd} {
      1 run_rbu 
      2 step_rbu 3 step_rbu_uri 4 step_rbu_state

          zSelect, pIter->zTbl, zOrder
        )
    );
    if( p->rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pSel) ){
      zSep = "";
      for(iCol=0; iCol<pIter->nCol; iCol++){
        const char *zQuoted = (const char*)sqlite3_column_text(pSel, iCol);
        if( zQuoted==0 ){
          p->rc = SQLITE_NOMEM;
        }else if( zQuoted[0]=='N' ){
          bFailed = 1;
          break;
        }
        zVector = rbuMPrintf(p, "%z%s%s", zVector, zSep, zQuoted);
        zSep = ", ";
      }

      ** or xOpen() to operate on the *-wal file.  */
      pFd->zWal = sqlite3_filename_wal(zName);
    }
    else if( flags & SQLITE_OPEN_WAL ){
      rbu_file *pDb = rbuFindMaindb(pRbuVfs, zName, 0);
      if( pDb ){
        if( pDb->pRbu && pDb->pRbu->eStage==RBU_STAGE_OAL ){
          /* This call is to open a *-wal file. Intead, open the *-oal. */




          size_t nOpen;

          if( rbuIsVacuum(pDb->pRbu) ){
            zOpen = sqlite3_db_filename(pDb->pRbu->dbRbu, "main");
            zOpen = sqlite3_filename_wal(zOpen);
          }
          nOpen = strlen(zOpen);



          ((char*)zOpen)[nOpen-3] = 'o';






          pFd->pRbu = pDb->pRbu;
        }
        pDb->pWalFd = pFd;
      }
    }
  }else{
    pFd->pRbu = pRbuVfs->pRbu;

**
** <li>[[SQLITE_FCNTL_CKPT_DONE]]
** The [SQLITE_FCNTL_CKPT_DONE] opcode is invoked from within a checkpoint
** in wal mode after the client has finished copying pages from the wal
** file to the database file, but before the *-shm file is updated to
** record the fact that the pages have been checkpointed.
** </ul>
**
** <li>[[SQLITE_FCNTL_CKSM_FILE]]
** Used by the cksmvfs VFS module only.
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE               1
#define SQLITE_FCNTL_GET_LOCKPROXYFILE       2
#define SQLITE_FCNTL_SET_LOCKPROXYFILE       3
#define SQLITE_FCNTL_LAST_ERRNO              4
#define SQLITE_FCNTL_SIZE_HINT               5
#define SQLITE_FCNTL_CHUNK_SIZE              6

#define SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE  33
#define SQLITE_FCNTL_LOCK_TIMEOUT           34
#define SQLITE_FCNTL_DATA_VERSION           35
#define SQLITE_FCNTL_SIZE_LIMIT             36
#define SQLITE_FCNTL_CKPT_DONE              37
#define SQLITE_FCNTL_RESERVE_BYTES          38
#define SQLITE_FCNTL_CKPT_START             39
#define SQLITE_FCNTL_EXTERNAL_READER        40
#define SQLITE_FCNTL_CKSM_FILE              41

/* deprecated names */
#define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE
#define SQLITE_SET_LOCKPROXYFILE      SQLITE_FCNTL_SET_LOCKPROXYFILE
#define SQLITE_LAST_ERRNO             SQLITE_FCNTL_LAST_ERRNO