}
    } {
      reset_db
      execsql $schema

      do_test $tn3.1.$tn2.$tn.1 {
        create_ota1 ota.db
        breakpoint
        $cmd test.db ota.db
      } {SQLITE_DONE}

      do_execsql_test $tn3.1.$tn2.$tn.2 { SELECT * FROM t1 ORDER BY a ASC } {
        1 2 3 
        2 two three 
        3 {} 8.2
................................................................................

      do_test $tn3.6.$tn {
        list [catch { run_ota test.db ota.db } msg] $msg
      } [list 1 $error]
    }
  }


  eval $destroy_vfs
}


finish_test

      }
    } {
      reset_db
      execsql $schema

      do_test $tn3.1.$tn2.$tn.1 {
        create_ota1 ota.db

        $cmd test.db ota.db
      } {SQLITE_DONE}

      do_execsql_test $tn3.1.$tn2.$tn.2 { SELECT * FROM t1 ORDER BY a ASC } {
        1 2 3 
        2 two three 
        3 {} 8.2
................................................................................

      do_test $tn3.6.$tn {
        list [catch { run_ota test.db ota.db } msg] $msg
      } [list 1 $error]
    }
  }

  catch { db close }
  eval $destroy_vfs
}


finish_test

    list [file exists test.db-oal] [file exists test.db-wal]
  } {1 0}
  do_test 1.$nStep.4 {
    list [catch { ota close } msg] $msg
  } {1 {SQLITE_BUSY - database modified during ota update}}
}

for {set nStep 7} {$nStep < 8} {incr nStep} {
  do_test 1.$nStep.1 {
    setup_test
    sqlite3ota ota test.db ota.db
    for {set i 0} {$i<$nStep} {incr i} {ota step}
    ota close
    sqlite3 db test.db
    execsql { INSERT INTO t1 VALUES(5, 'hello') }
    sqlite3ota ota test.db ota.db
    ota step
  } {SQLITE_OK}
  do_test 1.$nStep.2 {
    ota step
  } {SQLITE_OK}
  do_test 1.$nStep.3 {
    list [file exists test.db-oal] [file exists test.db-wal]
  } {0 1}
  do_test 1.$nStep.4 {
    list [catch { ota close } msg] $msg
  } {0 SQLITE_OK}
}


# Test the outcome of some other client writing the db after the *-oal
# file has been copied to the *-wal path. Once this has happened, any
# other client writing to the db causes OTA to consider its job finished.
#
for {set nStep 8} {$nStep < 20} {incr nStep} {
  do_test 1.$nStep.1 {
    setup_test
    sqlite3ota ota test.db ota.db
    for {set i 0} {$i<$nStep} {incr i} {ota step}
    ota close
    sqlite3 db test.db
    execsql { INSERT INTO t1 VALUES(5, 'hello') }

    list [file exists test.db-oal] [file exists test.db-wal]
  } {1 0}
  do_test 1.$nStep.4 {
    list [catch { ota close } msg] $msg
  } {1 {SQLITE_BUSY - database modified during ota update}}
}
























# Test the outcome of some other client writing the db after the *-oal
# file has been copied to the *-wal path. Once this has happened, any
# other client writing to the db causes OTA to consider its job finished.
#
for {set nStep 7} {$nStep < 20} {incr nStep} {
  do_test 1.$nStep.1 {
    setup_test
    sqlite3ota ota test.db ota.db
    for {set i 0} {$i<$nStep} {incr i} {ota step}
    ota close
    sqlite3 db test.db
    execsql { INSERT INTO t1 VALUES(5, 'hello') }

#define OTA_STATE_IDX         3
#define OTA_STATE_ROW         4
#define OTA_STATE_PROGRESS    5
#define OTA_STATE_CKPT        6
#define OTA_STATE_COOKIE      7

#define OTA_STAGE_OAL         1

#define OTA_STAGE_CKPT        3
#define OTA_STAGE_DONE        4


#define OTA_CREATE_STATE "CREATE TABLE IF NOT EXISTS ota.ota_state"        \
                             "(k INTEGER PRIMARY KEY, v)"

typedef struct OtaState OtaState;
typedef struct OtaObjIter OtaObjIter;
typedef struct ota_vfs ota_vfs;
typedef struct ota_file ota_file;
















/*
** A structure to store values read from the ota_state table in memory.
*/
struct OtaState {
  int eStage;
  char *zTbl;
  char *zIdx;
  unsigned char *pCkptState;
  int nCkptState;
  int nRow;
  sqlite3_int64 nProgress;
};

/*
** An iterator of this type is used to iterate through all objects in
** the target database that require updating. For each such table, the
** iterator visits, in order:
**
................................................................................
struct OtaObjIter {
  sqlite3_stmt *pTblIter;         /* Iterate through tables */
  sqlite3_stmt *pIdxIter;         /* Index iterator */
  int nTblCol;                    /* Size of azTblCol[] array */
  char **azTblCol;                /* Array of unquoted target column names */
  char **azTblType;               /* Array of target column types */
  int *aiSrcOrder;                /* src table col -> target table col */
  unsigned char *abTblPk;         /* Array of flags, set on target PK columns */
  unsigned char *abNotNull;       /* Array of flags, set on NOT NULL columns */
  int eType;                      /* Table type - an OTA_PK_XXX value */

  /* Output variables. zTbl==0 implies EOF. */
  int bCleanup;                   /* True in "cleanup" state */
  const char *zTbl;               /* Name of target db table */
  const char *zIdx;               /* Name of target db index (or null) */
  int iTnum;                      /* Root page of current object */
................................................................................
#define OTA_PK_NONE           1
#define OTA_PK_IPK            2
#define OTA_PK_EXTERNAL       3
#define OTA_PK_WITHOUT_ROWID  4
#define OTA_PK_VTAB           5








/*
** OTA handle.
*/
struct sqlite3ota {
  int eStage;                     /* Value of OTA_STATE_STAGE field */
  sqlite3 *db;                    /* "main" -> target db, "ota" -> ota db */
  char *zTarget;                  /* Path to target db */
  char *zOta;                     /* Path to ota db */
  int rc;                         /* Value returned by last ota_step() call */
  char *zErrmsg;                  /* Error message if rc!=SQLITE_OK */
  int nStep;                      /* Rows processed for current object */
  int nProgress;                  /* Rows processed for all objects */
  OtaObjIter objiter;             /* Iterator for skipping through tbl/idx */
  sqlite3_ckpt *pCkpt;            /* Incr-checkpoint handle */
  ota_file *pTargetFd;            /* File handle open on target db */
  const char *zVfsName;           /* Name of automatically created ota vfs */












};

struct ota_vfs {
  sqlite3_vfs base;             /* ota VFS shim methods */
  sqlite3_vfs *pRealVfs;        /* Underlying VFS */
  sqlite3_mutex *mutex;
  const char *zOtaWal;
};

struct ota_file {
  sqlite3_file base;              /* sqlite3_file methods */
  sqlite3_file *pReal;            /* Underlying file handle */
  ota_vfs *pOtaVfs;               /* Pointer to the ota_vfs object */
  sqlite3ota *pOta;               /* Pointer to ota object (ota target only) */

  int openFlags;                  /* Flags this file was opened with */
  unsigned int iCookie;           /* Cookie value for main db files */
  unsigned char iWriteVer;        /* "write-version" value for main db files */

  int nShm;                       /* Number of entries in apShm[] array */
  char **apShm;                   /* Array of mmap'd *-shm regions */
  const char *zWal;               /* Wal filename for this db file */
  char *zDel;                     /* Delete this when closing file */




};


static void otaCreateVfs(sqlite3ota*, const char*);
static void otaDeleteVfs(sqlite3ota*);

/*
................................................................................

/*
** Allocate and zero the pIter->azTblCol[] and abTblPk[] arrays so that
** there is room for at least nCol elements. If an OOM occurs, store an
** error code in the OTA handle passed as the first argument.
*/
static void otaAllocateIterArrays(sqlite3ota *p, OtaObjIter *pIter, int nCol){
  int nByte = (2*sizeof(char*) + sizeof(int) + 2*sizeof(unsigned char)) * nCol;
  char **azNew;

  azNew = (char**)otaMalloc(p, nByte);
  if( azNew ){
    pIter->azTblCol = azNew;
    pIter->azTblType = &azNew[nCol];
    pIter->aiSrcOrder = (int*)&pIter->azTblType[nCol];
    pIter->abTblPk = (unsigned char*)&pIter->aiSrcOrder[nCol];
    pIter->abNotNull = (unsigned char*)&pIter->abTblPk[nCol];
  }
}

static char *otaStrndup(const char *zStr, int nStr, int *pRc){
  char *zRet = 0;
  assert( *pRc==SQLITE_OK );

................................................................................
  zSql = sqlite3_mprintf("PRAGMA index_list=%Q",zTab);
  if( zSql==0 ) return SQLITE_NOMEM;
  rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
  sqlite3_free(zSql);
  zSql = 0;
  if( pStmt==0 ) goto otaTableType_end;
  while( sqlite3_step(pStmt)==SQLITE_ROW ){
    const unsigned char *zOrig = sqlite3_column_text(pStmt,3);
    if( zOrig && zOrig[0]=='p' ){
      zSql = sqlite3_mprintf("SELECT rootpage FROM main.sqlite_master"
                             " WHERE name=%Q", sqlite3_column_text(pStmt,1));
      if( zSql==0 ){ rc = SQLITE_NOMEM; goto otaTableType_end; }
      break;
    }
  }
................................................................................
        if( i!=iOrder ){
          SWAP(int, pIter->aiSrcOrder[i], pIter->aiSrcOrder[iOrder]);
          SWAP(char*, pIter->azTblCol[i], pIter->azTblCol[iOrder]);
        }

        pIter->azTblType[iOrder] = otaStrndup(zType, -1, &p->rc);
        pIter->abTblPk[iOrder] = (iPk!=0);
        pIter->abNotNull[iOrder] = (unsigned char)bNotNull || (iPk!=0);
        iOrder++;
      }
    }

    rc2 = sqlite3_finalize(pStmt);
    if( p->rc==SQLITE_OK ) p->rc = rc2;
  }
................................................................................
** error occurs, leave an error code and message in the OTA handle.
*/
static void otaOpenDatabase(sqlite3ota *p){
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
  assert( p->rc==SQLITE_OK );
  assert( p->db==0 );


  p->rc = sqlite3_open_v2(p->zTarget, &p->db, flags, p->zVfsName);
  if( p->rc ){
    p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(p->db));
  }else{


    otaMPrintfExec(p, "ATTACH %Q AS ota", p->zOta);


    /* Mark the database file just opened as an OTA target database. If 
    ** this call returns SQLITE_NOTFOUND, then the OTA vfs is not in use.
    ** This is an error.  */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_file_control(p->db, "main", SQLITE_FCNTL_OTA, (void*)p);


      if( p->rc==SQLITE_NOTFOUND ){
        p->rc = SQLITE_ERROR;
        p->zErrmsg = sqlite3_mprintf("ota vfs not found");
      }
    }
  }
}

/*
** This routine is a copy of the sqlite3FileSuffix3() routine from the core.
** It is a no-op unless SQLITE_ENABLE_8_3_NAMES is defined.
................................................................................
    int i, sz;
    sz = sqlite3Strlen30(z);
    for(i=sz-1; i>0 && z[i]!='/' && z[i]!='.'; i--){}
    if( z[i]=='.' && ALWAYS(sz>i+4) ) memmove(&z[i+1], &z[sz-3], 4);
  }
#endif
}
































































































/*
** The OTA handle is currently in OTA_STAGE_OAL state, with a SHARED lock
** on the database file. This proc moves the *-oal file to the *-wal path,
** then reopens the database file (this time in vanilla, non-oal, WAL mode).
** If an error occurs, leave an error code and error message in the ota 
** handle.
................................................................................
    otaFileSuffix3(zBase, zOal);
    rename(zOal, zWal);

    /* Re-open the databases. */
    otaObjIterFinalize(&p->objiter);
    sqlite3_close(p->db);
    p->db = 0;
    p->eStage = OTA_STAGE_CKPT;
    otaOpenDatabase(p);

  }

  sqlite3_free(zWal);
  sqlite3_free(zOal);
}

/*
................................................................................
            otaMoveOalFile(p);
          }
        }
        break;
      }

      case OTA_STAGE_CKPT: {



        if( p->rc==SQLITE_OK && p->pCkpt==0 ){
          p->rc = sqlite3_ckpt_open(p->db, 0, 0, &p->pCkpt);


        }

        if( p->rc==SQLITE_OK ){
          if( p->pCkpt==0 ){
            p->eStage = OTA_STAGE_DONE;
            p->rc = SQLITE_DONE;
          }else if( SQLITE_OK!=sqlite3_ckpt_step(p->pCkpt) ){
            p->rc = sqlite3_ckpt_close(p->pCkpt, 0, 0);
            p->pCkpt = 0;




            if( p->rc==SQLITE_OK ){
              p->eStage = OTA_STAGE_DONE;
              p->rc = SQLITE_DONE;
            }




          }
          p->nProgress++;
        }


        break;
      }

      default:
        break;
    }
    return p->rc;
  }else{
    return SQLITE_NOMEM;
  }
}

static void otaSaveTransactionState(sqlite3ota *p){
  sqlite3_stmt *pInsert;
  int rc;

  assert( (p->rc==SQLITE_OK || p->rc==SQLITE_DONE) && p->zErrmsg==0 );
  rc = prepareFreeAndCollectError(p->db, &pInsert, &p->zErrmsg, 
      sqlite3_mprintf(
        "INSERT OR REPLACE INTO ota.ota_state(k, v) VALUES "
        "(%d, %d), "
        "(%d, %Q), "
        "(%d, %Q), "
        "(%d, %d), "
        "(%d, %lld), "
        "(%d, ?), "
        "(%d, %lld) ",
        OTA_STATE_STAGE, p->eStage,
        OTA_STATE_TBL, p->objiter.zTbl, 
        OTA_STATE_IDX, p->objiter.zIdx, 
        OTA_STATE_ROW, p->nStep, 
        OTA_STATE_PROGRESS, p->nProgress,
        OTA_STATE_CKPT,
        OTA_STATE_COOKIE, (sqlite3_int64)p->pTargetFd->iCookie
      )
  );
  assert( pInsert==0 || rc==SQLITE_OK );
  if( rc==SQLITE_OK ){
    if( p->pCkpt ){
      unsigned char *pCkptState = 0;
      int nCkptState = 0;
      rc = sqlite3_ckpt_close(p->pCkpt, &pCkptState, &nCkptState);
      p->pCkpt = 0;
      sqlite3_bind_blob(pInsert, 1, pCkptState, nCkptState, SQLITE_TRANSIENT);
      sqlite3_free(pCkptState);
    }
  }
  if( rc==SQLITE_OK ){
    sqlite3_step(pInsert);
    rc = sqlite3_finalize(pInsert);
  }else{
    sqlite3_finalize(pInsert);
  }

................................................................................
  }
}

static void otaFreeState(OtaState *p){
  if( p ){
    sqlite3_free(p->zTbl);
    sqlite3_free(p->zIdx);
    sqlite3_free(p->pCkptState);
    sqlite3_free(p);
  }
}

/*
** Allocate an OtaState object and load the contents of the ota_state 
** table into it. Return a pointer to the new object. It is the 
................................................................................
        break;

      case OTA_STATE_PROGRESS:
        pRet->nProgress = sqlite3_column_int64(pStmt, 1);
        break;

      case OTA_STATE_CKPT:
        pRet->nCkptState = sqlite3_column_bytes(pStmt, 1);
        pRet->pCkptState = (unsigned char*)otaStrndup(
            (char*)sqlite3_column_blob(pStmt, 1), pRet->nCkptState, &rc
        );
        break;

      case OTA_STATE_COOKIE:
        /* At this point (p->iCookie) contains the value of the change-counter
        ** cookie (the thing that gets incremented when a transaction is 
        ** committed in rollback mode) currently stored on page 1 of the 
        ** database file. */
        if( pRet->eStage==OTA_STAGE_OAL 
         && p->pTargetFd->iCookie!=(unsigned int)sqlite3_column_int64(pStmt, 1) 
        ){
          rc = SQLITE_BUSY;
          p->zErrmsg = sqlite3_mprintf("database modified during ota update");
        }
        break;

      default:
................................................................................
  int nTarget = strlen(zTarget);
  int nOta = strlen(zOta);

  p = (sqlite3ota*)sqlite3_malloc(sizeof(sqlite3ota)+nTarget+1+nOta+1);
  if( p ){
    OtaState *pState = 0;

    /* Create the custom VFS */
    memset(p, 0, sizeof(sqlite3ota));
    otaCreateVfs(p, 0);

    /* Open the target database */
    if( p->rc==SQLITE_OK ){
      p->zTarget = (char*)&p[1];
      memcpy(p->zTarget, zTarget, nTarget+1);
................................................................................
    }

    /* If it has not already been created, create the ota_state table */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->db, OTA_CREATE_STATE, 0, 0, &p->zErrmsg);
    }






    if( p->rc==SQLITE_OK && p->pTargetFd->iWriteVer>1 ){
      p->rc = SQLITE_ERROR;
      p->zErrmsg = sqlite3_mprintf("cannot update wal mode database");
    }

    if( p->rc==SQLITE_OK ){
      pState = otaLoadState(p);
      assert( pState || p->rc!=SQLITE_OK );
      if( p->rc==SQLITE_OK ){
        if( pState->eStage==0 ){ 
          otaDeleteOalFile(p);
          p->eStage = 1;
        }else{
          p->eStage = pState->eStage;
        }
        p->nProgress = pState->nProgress;
      }
    }
    assert( p->rc!=SQLITE_OK || p->eStage!=0 );

    if( p->rc==SQLITE_OK ){
      if( p->eStage==OTA_STAGE_OAL ){
        ota_vfs *pOtaVfs = p->pTargetFd->pOtaVfs;


        sqlite3_mutex_enter(pOtaVfs->mutex);
        assert( pOtaVfs->zOtaWal==0 );
        pOtaVfs->zOtaWal = p->pTargetFd->zWal;
        p->rc = sqlite3_exec(p->db, "BEGIN IMMEDIATE", 0, 0, &p->zErrmsg);
        pOtaVfs->zOtaWal = 0;
        sqlite3_mutex_leave(pOtaVfs->mutex);

  
        /* Point the object iterator at the first object */
        if( p->rc==SQLITE_OK ){
          p->rc = otaObjIterFirst(p, &p->objiter);
        }
  
        if( p->rc==SQLITE_OK ){
          otaLoadTransactionState(p, pState);
        }
      }else if( p->eStage==OTA_STAGE_CKPT ){
        p->rc = sqlite3_ckpt_open(
            p->db, pState->pCkptState, pState->nCkptState, &p->pCkpt
        );
        if( p->rc==SQLITE_MISMATCH || (p->rc==SQLITE_OK && p->pCkpt==0) ){
          p->eStage = OTA_STAGE_DONE;
          p->rc = SQLITE_DONE;
        }
      }else if( p->eStage==OTA_STAGE_DONE ){
        p->rc = SQLITE_DONE;
      }
    }

    otaFreeState(pState);
  }
................................................................................

    /* If the update has not been fully applied, save the state in 
    ** the ota db. If successful, this call also commits the open 
    ** transaction on the ota db. */
    assert( p->rc!=SQLITE_ROW );
    if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
      assert( p->zErrmsg==0 );
      otaSaveTransactionState(p);
    }

    /* Close any open statement handles. */
    otaObjIterFinalize(&p->objiter);

    /* Commit the transaction to the *-oal file. */
    if( p->rc==SQLITE_OK && p->eStage==OTA_STAGE_OAL ){
      p->rc = sqlite3_exec(p->db, "COMMIT", 0, 0, &p->zErrmsg);
    }

    /* Close the open database handle and VFS object. */
    if( p->pCkpt ) sqlite3_ckpt_close(p->pCkpt, 0, 0);
    sqlite3_close(p->db);
    otaDeleteVfs(p);



    otaEditErrmsg(p);
    rc = p->rc;
    *pzErrmsg = p->zErrmsg;
    sqlite3_free(p);
  }else{
    rc = SQLITE_NOMEM;
................................................................................
  /* Free the contents of the apShm[] array. And the array itself. */
  for(i=0; i<p->nShm; i++){
    sqlite3_free(p->apShm[i]);
  }
  sqlite3_free(p->apShm);
  p->apShm = 0;
  sqlite3_free(p->zDel);









  /* Close the underlying file handle */
  rc = p->pReal->pMethods->xClose(p->pReal);
  return rc;
}


/*
** Read and return an unsigned 32-bit big-endian integer from the buffer 
** passed as the only argument.
*/
static unsigned int otaGetU32(unsigned char *aBuf){
  return ((unsigned int)aBuf[0] << 24)
       + ((unsigned int)aBuf[1] << 16)
       + ((unsigned int)aBuf[2] <<  8)
       + ((unsigned int)aBuf[3]);
}

/*
** Read data from an otaVfs-file.
*/
static int otaVfsRead(
  sqlite3_file *pFile, 
  void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  ota_file *p = (ota_file*)pFile;








  int rc = p->pReal->pMethods->xRead(p->pReal, zBuf, iAmt, iOfst);
  if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
    /* These look like magic numbers. But they are stable, as they are part
    ** of the definition of the SQLite file format, which may not change. */
    unsigned char *pBuf = (unsigned char*)zBuf;

    p->iCookie = otaGetU32(&pBuf[24]);
    p->iWriteVer = pBuf[19];

  }
  return rc;
}

/*
** Write data to an otaVfs-file.
*/
................................................................................
static int otaVfsWrite(
  sqlite3_file *pFile, 
  const void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  ota_file *p = (ota_file*)pFile;







  int rc = p->pReal->pMethods->xWrite(p->pReal, zBuf, iAmt, iOfst);
  if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
    /* These look like magic numbers. But they are stable, as they are part
    ** of the definition of the SQLite file format, which may not change. */
    unsigned char *pBuf = (unsigned char*)zBuf;

    p->iCookie = otaGetU32(&pBuf[24]);
    p->iWriteVer = pBuf[19];

  }
  return rc;
}

/*
** Truncate an otaVfs-file.
*/
................................................................................
}

/*
** Sync an otaVfs-file.
*/
static int otaVfsSync(sqlite3_file *pFile, int flags){
  ota_file *p = (ota_file *)pFile;






  return p->pReal->pMethods->xSync(p->pReal, flags);
}

/*
** Return the current file-size of an otaVfs-file.
*/
static int otaVfsFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
................................................................................
** Lock an otaVfs-file.
*/
static int otaVfsLock(sqlite3_file *pFile, int eLock){
  ota_file *p = (ota_file*)pFile;
  sqlite3ota *pOta = p->pOta;
  int rc = SQLITE_OK;

  if( pOta && eLock==SQLITE_LOCK_EXCLUSIVE
   && (pOta->eStage==OTA_STAGE_OAL || pOta->eStage==OTA_STAGE_CKPT) 
  ){
    /* Do not allow EXCLUSIVE locks. Preventing SQLite from taking this 
    ** prevents it from checkpointing the database from sqlite3_close(). */
    rc = SQLITE_BUSY;
  }else{
    rc = p->pReal->pMethods->xLock(p->pReal, eLock);
  }

................................................................................
/*
** File control method. For custom operations on an otaVfs-file.
*/
static int otaVfsFileControl(sqlite3_file *pFile, int op, void *pArg){
  ota_file *p = (ota_file *)pFile;
  int (*xControl)(sqlite3_file*,int,void*) = p->pReal->pMethods->xFileControl;


  if( op==SQLITE_FCNTL_OTA ){
    int rc;
    sqlite3ota *pOta = (sqlite3ota*)pArg;

    /* First try to find another OTA vfs lower down in the vfs stack. If
    ** one is found, this vfs will operate in pass-through mode. The lower
    ** level vfs will do the special OTA handling.  */
................................................................................
      rc = xControl(p->pReal, SQLITE_FCNTL_ZIPVFS_PAGER, &dummy);
      if( rc==SQLITE_OK ){
        rc = SQLITE_ERROR;
        pOta->zErrmsg = sqlite3_mprintf("ota/zipvfs setup error");
      }else if( rc==SQLITE_NOTFOUND ){
        pOta->pTargetFd = p;
        p->pOta = pOta;

        rc = SQLITE_OK;
      }
    }
    return rc;
  }
  return xControl(p->pReal, op, pArg);
}
................................................................................
}

/*
** Shared-memory methods are all pass-thrus.
*/
static int otaVfsShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  ota_file *p = (ota_file*)pFile;

  int rc = SQLITE_OK;

#ifdef SQLITE_AMALGAMATION
    assert( WAL_CKPT_LOCK==1 );
#endif


  if( p->pOta && p->pOta->eStage==OTA_STAGE_OAL ){
    /* Magic number 1 is the WAL_CKPT_LOCK lock. Preventing SQLite from
    ** taking this lock also prevents any checkpoints from occurring. 
    ** todo: really, it's not clear why this might occur, as 
    ** wal_autocheckpoint ought to be turned off.  */
    if( ofst==1 && n==1 ) rc = SQLITE_BUSY;
  }else{
    assert( p->nShm==0 );








    rc = p->pReal->pMethods->xShmLock(p->pReal, ofst, n, flags);




  }

  return rc;
}

static int otaVfsShmMap(
  sqlite3_file *pFile, 
................................................................................
){
  ota_file *p = (ota_file*)pFile;
  int rc = SQLITE_OK;

  /* If not in OTA_STAGE_OAL, allow this call to pass through. Or, if this
  ** ota is in the OTA_STAGE_OAL state, use heap memory for *-shm space 
  ** instead of a file on disk.  */

  if( p->pOta && p->pOta->eStage==OTA_STAGE_OAL ){
    if( iRegion<=p->nShm ){
      int nByte = (iRegion+1) * sizeof(char*);
      char **apNew = (char**)sqlite3_realloc(p->apShm, nByte);
      if( apNew==0 ){
        rc = SQLITE_NOMEM;
      }else{
................................................................................
  p->pReal->pMethods->xShmBarrier(p->pReal);
}

static int otaVfsShmUnmap(sqlite3_file *pFile, int delFlag){
  ota_file *p = (ota_file*)pFile;
  int rc = SQLITE_OK;


  if( p->pOta && p->pOta->eStage==OTA_STAGE_OAL ){
    /* no-op */
  }else{
    rc = p->pReal->pMethods->xShmUnmap(p->pReal, delFlag);
  }
  return rc;
}









/*
** Open an ota file handle.
*/
static int otaVfsOpen(
  sqlite3_vfs *pVfs,
  const char *zName,
................................................................................
        z += 2;
      }else{
        while( *z==0 ) z++;
      }
      z += (n + 8 + 1);
      pFd->zWal = z;
    }
    else if( (flags & SQLITE_OPEN_WAL) && zName==pOtaVfs->zOtaWal ){



      char *zCopy = otaStrndup(zName, -1, &rc);
      if( zCopy ){
        int nCopy = strlen(zCopy);
        zCopy[nCopy-3] = 'o';
        zOpen = (const char*)(pFd->zDel = zCopy);




      }
    }
  }

  if( rc==SQLITE_OK ){
    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, flags, pOutFlags);
  }
  if( pFd->pReal->pMethods ){



    pFile->pMethods = &otavfs_io_methods;






  }

  return rc;
}

/*
** Delete the file located at zPath.
................................................................................
){
  ota_vfs *pOtaVfs = (ota_vfs*)pVfs;
  sqlite3_vfs *pRealVfs = pOtaVfs->pRealVfs;
  int rc;

  rc = pRealVfs->xAccess(pRealVfs, zPath, flags, pResOut);















  if( rc==SQLITE_OK && flags==SQLITE_ACCESS_EXISTS && pOtaVfs->zOtaWal==zPath ){


    if( *pResOut ){
      rc = SQLITE_CANTOPEN;
    }else{
      *pResOut = 1;

    }
  }

  return rc;
}

/*

#define OTA_STATE_IDX         3
#define OTA_STATE_ROW         4
#define OTA_STATE_PROGRESS    5
#define OTA_STATE_CKPT        6
#define OTA_STATE_COOKIE      7

#define OTA_STAGE_OAL         1
#define OTA_STAGE_CAPTURE     2
#define OTA_STAGE_CKPT        3
#define OTA_STAGE_DONE        4


#define OTA_CREATE_STATE "CREATE TABLE IF NOT EXISTS ota.ota_state"        \
                             "(k INTEGER PRIMARY KEY, v)"

typedef struct OtaState OtaState;
typedef struct OtaObjIter OtaObjIter;
typedef struct ota_vfs ota_vfs;
typedef struct ota_file ota_file;

#if !defined(SQLITE_AMALGAMATION)
typedef unsigned int u32;
typedef unsigned char u8;
typedef sqlite3_int64 i64;
#endif

/*
** These values must match the values defined in wal.c for the equivalent
** locks. These are not magic numbers as they are part of the SQLite file
** format.
*/
#define WAL_LOCK_WRITE  0
#define WAL_LOCK_CKPT   1
#define WAL_LOCK_READ0  3

/*
** A structure to store values read from the ota_state table in memory.
*/
struct OtaState {
  int eStage;
  char *zTbl;
  char *zIdx;
  i64 iWalCksum;

  int nRow;
  i64 nProgress;
};

/*
** An iterator of this type is used to iterate through all objects in
** the target database that require updating. For each such table, the
** iterator visits, in order:
**
................................................................................
struct OtaObjIter {
  sqlite3_stmt *pTblIter;         /* Iterate through tables */
  sqlite3_stmt *pIdxIter;         /* Index iterator */
  int nTblCol;                    /* Size of azTblCol[] array */
  char **azTblCol;                /* Array of unquoted target column names */
  char **azTblType;               /* Array of target column types */
  int *aiSrcOrder;                /* src table col -> target table col */
  u8 *abTblPk;                    /* Array of flags, set on target PK columns */
  u8 *abNotNull;                  /* Array of flags, set on NOT NULL columns */
  int eType;                      /* Table type - an OTA_PK_XXX value */

  /* Output variables. zTbl==0 implies EOF. */
  int bCleanup;                   /* True in "cleanup" state */
  const char *zTbl;               /* Name of target db table */
  const char *zIdx;               /* Name of target db index (or null) */
  int iTnum;                      /* Root page of current object */
................................................................................
#define OTA_PK_NONE           1
#define OTA_PK_IPK            2
#define OTA_PK_EXTERNAL       3
#define OTA_PK_WITHOUT_ROWID  4
#define OTA_PK_VTAB           5


typedef struct OtaFrame OtaFrame;
struct OtaFrame {
  u32 iDbPage;
  u32 iWalFrame;
};

/*
** OTA handle.
*/
struct sqlite3ota {
  int eStage;                     /* Value of OTA_STATE_STAGE field */
  sqlite3 *db;                    /* "main" -> target db, "ota" -> ota db */
  char *zTarget;                  /* Path to target db */
  char *zOta;                     /* Path to ota db */
  int rc;                         /* Value returned by last ota_step() call */
  char *zErrmsg;                  /* Error message if rc!=SQLITE_OK */
  int nStep;                      /* Rows processed for current object */
  int nProgress;                  /* Rows processed for all objects */
  OtaObjIter objiter;             /* Iterator for skipping through tbl/idx */
  const char *zVfsName;           /* Name of automatically created ota vfs */
  ota_file *pTargetFd;            /* File handle open on target db */


  /* The following state variables are used as part of the incremental
  ** checkpoint stage (eStage==OTA_STAGE_CKPT). See function otaSetupCkpt()
  ** for details.  */
  u32 iMaxFrame;                  /* Largest iWalFrame value in aFrame[] */
  u32 mLock;
  int nFrame;                     /* Entries in aFrame[] array */
  int nFrameAlloc;                /* Allocated size of aFrame[] array */
  OtaFrame *aFrame;
  int pgsz;
  u8 *aBuf;
  i64 iWalCksum;
};

struct ota_vfs {
  sqlite3_vfs base;               /* ota VFS shim methods */
  sqlite3_vfs *pRealVfs;          /* Underlying VFS */
  sqlite3_mutex *mutex;           /* Mutex to protect pMain */
  ota_file *pMain;                /* Linked list of main db files */
};

struct ota_file {
  sqlite3_file base;              /* sqlite3_file methods */
  sqlite3_file *pReal;            /* Underlying file handle */
  ota_vfs *pOtaVfs;               /* Pointer to the ota_vfs object */
  sqlite3ota *pOta;               /* Pointer to ota object (ota target only) */

  int openFlags;                  /* Flags this file was opened with */
  u32 iCookie;                    /* Cookie value for main db files */
  u8 iWriteVer;                   /* "write-version" value for main db files */

  int nShm;                       /* Number of entries in apShm[] array */
  char **apShm;                   /* Array of mmap'd *-shm regions */

  char *zDel;                     /* Delete this when closing file */

  const char *zWal;               /* Wal filename for this main db file */
  ota_file *pWalFd;               /* Wal file descriptor for this main db */
  ota_file *pMainNext;            /* Next MAIN_DB file */
};


static void otaCreateVfs(sqlite3ota*, const char*);
static void otaDeleteVfs(sqlite3ota*);

/*
................................................................................

/*
** Allocate and zero the pIter->azTblCol[] and abTblPk[] arrays so that
** there is room for at least nCol elements. If an OOM occurs, store an
** error code in the OTA handle passed as the first argument.
*/
static void otaAllocateIterArrays(sqlite3ota *p, OtaObjIter *pIter, int nCol){
  int nByte = (2*sizeof(char*) + sizeof(int) + 2*sizeof(u8)) * nCol;
  char **azNew;

  azNew = (char**)otaMalloc(p, nByte);
  if( azNew ){
    pIter->azTblCol = azNew;
    pIter->azTblType = &azNew[nCol];
    pIter->aiSrcOrder = (int*)&pIter->azTblType[nCol];
    pIter->abTblPk = (u8*)&pIter->aiSrcOrder[nCol];
    pIter->abNotNull = (u8*)&pIter->abTblPk[nCol];
  }
}

static char *otaStrndup(const char *zStr, int nStr, int *pRc){
  char *zRet = 0;
  assert( *pRc==SQLITE_OK );

................................................................................
  zSql = sqlite3_mprintf("PRAGMA index_list=%Q",zTab);
  if( zSql==0 ) return SQLITE_NOMEM;
  rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
  sqlite3_free(zSql);
  zSql = 0;
  if( pStmt==0 ) goto otaTableType_end;
  while( sqlite3_step(pStmt)==SQLITE_ROW ){
    const u8 *zOrig = sqlite3_column_text(pStmt,3);
    if( zOrig && zOrig[0]=='p' ){
      zSql = sqlite3_mprintf("SELECT rootpage FROM main.sqlite_master"
                             " WHERE name=%Q", sqlite3_column_text(pStmt,1));
      if( zSql==0 ){ rc = SQLITE_NOMEM; goto otaTableType_end; }
      break;
    }
  }
................................................................................
        if( i!=iOrder ){
          SWAP(int, pIter->aiSrcOrder[i], pIter->aiSrcOrder[iOrder]);
          SWAP(char*, pIter->azTblCol[i], pIter->azTblCol[iOrder]);
        }

        pIter->azTblType[iOrder] = otaStrndup(zType, -1, &p->rc);
        pIter->abTblPk[iOrder] = (iPk!=0);
        pIter->abNotNull[iOrder] = (u8)bNotNull || (iPk!=0);
        iOrder++;
      }
    }

    rc2 = sqlite3_finalize(pStmt);
    if( p->rc==SQLITE_OK ) p->rc = rc2;
  }
................................................................................
** error occurs, leave an error code and message in the OTA handle.
*/
static void otaOpenDatabase(sqlite3ota *p){
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
  assert( p->rc==SQLITE_OK );
  assert( p->db==0 );

  p->eStage = 0;
  p->rc = sqlite3_open_v2(p->zTarget, &p->db, flags, p->zVfsName);
  if( p->rc ){
    p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(p->db));
  }else{
    p->rc = sqlite3_file_control(p->db, "main", SQLITE_FCNTL_OTA, (void*)p);
    if( p->rc==SQLITE_OK ){
      otaMPrintfExec(p, "ATTACH %Q AS ota", p->zOta);
    }

    /* Mark the database file just opened as an OTA target database. If 
    ** this call returns SQLITE_NOTFOUND, then the OTA vfs is not in use.
    ** This is an error.  */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_file_control(p->db, "main", SQLITE_FCNTL_OTA, (void*)p);
    }

    if( p->rc==SQLITE_NOTFOUND ){
      p->rc = SQLITE_ERROR;
      p->zErrmsg = sqlite3_mprintf("ota vfs not found");

    }
  }
}

/*
** This routine is a copy of the sqlite3FileSuffix3() routine from the core.
** It is a no-op unless SQLITE_ENABLE_8_3_NAMES is defined.
................................................................................
    int i, sz;
    sz = sqlite3Strlen30(z);
    for(i=sz-1; i>0 && z[i]!='/' && z[i]!='.'; i--){}
    if( z[i]=='.' && ALWAYS(sz>i+4) ) memmove(&z[i+1], &z[sz-3], 4);
  }
#endif
}

/*
** Return the current wal-index header checksum for the target database 
** as a 64-bit integer.
**
** The checksum is store in the first page of xShmMap memory as an 8-byte 
** blob starting at byte offset 40.
*/
static i64 otaShmChecksum(sqlite3ota *p){
  i64 iRet;
  if( p->rc==SQLITE_OK ){
    sqlite3_file *pDb = p->pTargetFd->pReal;
    u32 volatile *ptr;
    p->rc = pDb->pMethods->xShmMap(pDb, 0, 32*1024, 0, (void volatile**)&ptr);
    if( p->rc==SQLITE_OK ){
      iRet = ((i64)ptr[10] << 32) + ptr[11];
    }
  }
  return iRet;
}

static void otaSetupCheckpoint(sqlite3ota *p, OtaState *pState){

  if( pState==0 ){
    p->eStage = 0;
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->db, "SELECT * FROM sqlite_master", 0, 0, 0);
    }
  }

  if( p->rc==SQLITE_OK ){
    int rc2;
    p->eStage = OTA_STAGE_CAPTURE;
    rc2 = sqlite3_exec(p->db, "PRAGMA main.wal_checkpoint=restart", 0, 0, 0);
    if( rc2!=SQLITE_INTERNAL ) p->rc = rc2;
  }

  if( p->rc==SQLITE_OK ){
    p->eStage = OTA_STAGE_CKPT;
    p->nStep = 0;
    p->aBuf = otaMalloc(p, p->pgsz);
    p->iWalCksum = otaShmChecksum(p);
  }

  if( p->rc==SQLITE_OK && pState && pState->iWalCksum!=p->iWalCksum ){
    p->rc = SQLITE_DONE;
    p->eStage = OTA_STAGE_DONE;
  }
}

static int otaCaptureWalRead(sqlite3ota *pOta, i64 iOff, int iAmt){
  const u32 mReq = (1<<WAL_LOCK_WRITE)|(1<<WAL_LOCK_CKPT)|(1<<WAL_LOCK_READ0);
  u32 iFrame;

  if( pOta->mLock!=mReq ){
    return SQLITE_BUSY;
  }

  pOta->pgsz = iAmt;
  if( pOta->nFrame==pOta->nFrameAlloc ){
    int nNew = (pOta->nFrameAlloc ? pOta->nFrameAlloc : 64) * 2;
    OtaFrame *aNew;
    aNew = (OtaFrame*)sqlite3_realloc(pOta->aFrame, nNew * sizeof(OtaFrame));
    if( aNew==0 ) return SQLITE_NOMEM;
    pOta->aFrame = aNew;
    pOta->nFrameAlloc = nNew;
  }

  iFrame = (u32)((iOff-32) / (i64)(iAmt+24)) + 1;
  if( pOta->iMaxFrame<iFrame ) pOta->iMaxFrame = iFrame;
  pOta->aFrame[pOta->nFrame].iWalFrame = iFrame;
  pOta->aFrame[pOta->nFrame].iDbPage = 0;
  pOta->nFrame++;
  return SQLITE_OK;
}

static int otaCaptureDbWrite(sqlite3ota *pOta, i64 iOff){
  pOta->aFrame[pOta->nFrame-1].iDbPage = (u32)(iOff / pOta->pgsz) + 1;
  return SQLITE_OK;
}

static void otaCheckpointFrame(sqlite3ota *p, OtaFrame *pFrame){
  if( p->rc==SQLITE_OK ){
    sqlite3_file *pWal = p->pTargetFd->pWalFd->pReal;
    sqlite3_file *pDb = p->pTargetFd->pReal;
    i64 iOff;

    iOff = (i64)(pFrame->iWalFrame-1) * (p->pgsz + 24) + 32 + 24;
    p->rc = pWal->pMethods->xRead(pWal, p->aBuf, p->pgsz, iOff);
    if( p->rc ) return;

    iOff = (i64)(pFrame->iDbPage-1) * p->pgsz;
    p->rc = pDb->pMethods->xWrite(pDb, p->aBuf, p->pgsz, iOff);
  }
}

/*
** The OTA handle is currently in OTA_STAGE_OAL state, with a SHARED lock
** on the database file. This proc moves the *-oal file to the *-wal path,
** then reopens the database file (this time in vanilla, non-oal, WAL mode).
** If an error occurs, leave an error code and error message in the ota 
** handle.
................................................................................
    otaFileSuffix3(zBase, zOal);
    rename(zOal, zWal);

    /* Re-open the databases. */
    otaObjIterFinalize(&p->objiter);
    sqlite3_close(p->db);
    p->db = 0;

    otaOpenDatabase(p);
    otaSetupCheckpoint(p, 0);
  }

  sqlite3_free(zWal);
  sqlite3_free(zOal);
}

/*
................................................................................
            otaMoveOalFile(p);
          }
        }
        break;
      }

      case OTA_STAGE_CKPT: {
        if( p->nStep>=p->nFrame ){
          sqlite3_file *pDb = p->pTargetFd->pReal;



          /* Sync the db file */
          p->rc = pDb->pMethods->xSync(pDb, SQLITE_SYNC_NORMAL);

          /* Update nBackfill */
          if( p->rc==SQLITE_OK ){



            void volatile *ptr;
            p->rc = pDb->pMethods->xShmMap(pDb, 0, 32*1024, 0, &ptr);
            if( p->rc==SQLITE_OK ){
              ((u32*)ptr)[12] = p->iMaxFrame;
            }
          }

          if( p->rc==SQLITE_OK ){
            p->eStage = OTA_STAGE_DONE;
            p->rc = SQLITE_DONE;
          }
        }else{
          OtaFrame *pFrame = &p->aFrame[p->nStep];
          otaCheckpointFrame(p, pFrame);
          p->nStep++;
        }



        p->nProgress++;
        break;
      }

      default:
        break;
    }
    return p->rc;
  }else{
    return SQLITE_NOMEM;
  }
}

static void otaSaveState(sqlite3ota *p){
  sqlite3_stmt *pInsert;
  int rc;

  assert( (p->rc==SQLITE_OK || p->rc==SQLITE_DONE) && p->zErrmsg==0 );
  rc = prepareFreeAndCollectError(p->db, &pInsert, &p->zErrmsg, 
      sqlite3_mprintf(
        "INSERT OR REPLACE INTO ota.ota_state(k, v) VALUES "
        "(%d, %d), "
        "(%d, %Q), "
        "(%d, %Q), "
        "(%d, %d), "
        "(%d, %lld), "
        "(%d, %lld), "
        "(%d, %lld) ",
        OTA_STATE_STAGE, p->eStage,
        OTA_STATE_TBL, p->objiter.zTbl, 
        OTA_STATE_IDX, p->objiter.zIdx, 
        OTA_STATE_ROW, p->nStep, 
        OTA_STATE_PROGRESS, p->nProgress,
        OTA_STATE_CKPT, p->iWalCksum,
        OTA_STATE_COOKIE, (i64)p->pTargetFd->iCookie
      )
  );
  assert( pInsert==0 || rc==SQLITE_OK );










  if( rc==SQLITE_OK ){
    sqlite3_step(pInsert);
    rc = sqlite3_finalize(pInsert);
  }else{
    sqlite3_finalize(pInsert);
  }

................................................................................
  }
}

static void otaFreeState(OtaState *p){
  if( p ){
    sqlite3_free(p->zTbl);
    sqlite3_free(p->zIdx);

    sqlite3_free(p);
  }
}

/*
** Allocate an OtaState object and load the contents of the ota_state 
** table into it. Return a pointer to the new object. It is the 
................................................................................
        break;

      case OTA_STATE_PROGRESS:
        pRet->nProgress = sqlite3_column_int64(pStmt, 1);
        break;

      case OTA_STATE_CKPT:
        pRet->iWalCksum = sqlite3_column_int64(pStmt, 1);



        break;

      case OTA_STATE_COOKIE:
        /* At this point (p->iCookie) contains the value of the change-counter
        ** cookie (the thing that gets incremented when a transaction is 
        ** committed in rollback mode) currently stored on page 1 of the 
        ** database file. */
        if( pRet->eStage==OTA_STAGE_OAL 
         && p->pTargetFd->iCookie!=(u32)sqlite3_column_int64(pStmt, 1) 
        ){
          rc = SQLITE_BUSY;
          p->zErrmsg = sqlite3_mprintf("database modified during ota update");
        }
        break;

      default:
................................................................................
  int nTarget = strlen(zTarget);
  int nOta = strlen(zOta);

  p = (sqlite3ota*)sqlite3_malloc(sizeof(sqlite3ota)+nTarget+1+nOta+1);
  if( p ){
    OtaState *pState = 0;

    /* Create the custom VFS. */
    memset(p, 0, sizeof(sqlite3ota));
    otaCreateVfs(p, 0);

    /* Open the target database */
    if( p->rc==SQLITE_OK ){
      p->zTarget = (char*)&p[1];
      memcpy(p->zTarget, zTarget, nTarget+1);
................................................................................
    }

    /* If it has not already been created, create the ota_state table */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->db, OTA_CREATE_STATE, 0, 0, &p->zErrmsg);
    }

    /* Check that this is not a wal mode database. If it is, it cannot be
    ** updated. There is also a check for a live *-wal file in otaVfsAccess()
    ** function, on the off chance that the target is a wal database for
    ** which the first page of the db file has been overwritten by garbage
    ** during an earlier failed checkpoint.  */
    if( p->rc==SQLITE_OK && p->pTargetFd->iWriteVer>1 ){
      p->rc = SQLITE_ERROR;
      p->zErrmsg = sqlite3_mprintf("cannot update wal mode database");
    }

    if( p->rc==SQLITE_OK ){
      pState = otaLoadState(p);
      assert( pState || p->rc!=SQLITE_OK );
      if( p->rc==SQLITE_OK ){
        if( pState->eStage==0 ){ 
          otaDeleteOalFile(p);
          p->eStage = OTA_STAGE_OAL;
        }else{
          p->eStage = pState->eStage;
        }
        p->nProgress = pState->nProgress;
      }
    }
    assert( p->rc!=SQLITE_OK || p->eStage!=0 );

    if( p->rc==SQLITE_OK ){
      if( p->eStage==OTA_STAGE_OAL ){


        /* Open the transaction */
        if( p->rc==SQLITE_OK ){


          p->rc = sqlite3_exec(p->db, "BEGIN IMMEDIATE", 0, 0, &p->zErrmsg);


        }
  
        /* Point the object iterator at the first object */
        if( p->rc==SQLITE_OK ){
          p->rc = otaObjIterFirst(p, &p->objiter);
        }
  
        if( p->rc==SQLITE_OK ){
          otaLoadTransactionState(p, pState);
        }
      }else if( p->eStage==OTA_STAGE_CKPT ){
        otaSetupCheckpoint(p, pState);
        p->nStep = pState->nRow;





      }else if( p->eStage==OTA_STAGE_DONE ){
        p->rc = SQLITE_DONE;
      }
    }

    otaFreeState(pState);
  }
................................................................................

    /* If the update has not been fully applied, save the state in 
    ** the ota db. If successful, this call also commits the open 
    ** transaction on the ota db. */
    assert( p->rc!=SQLITE_ROW );
    if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
      assert( p->zErrmsg==0 );
      otaSaveState(p);
    }

    /* Close any open statement handles. */
    otaObjIterFinalize(&p->objiter);

    /* Commit the transaction to the *-oal file. */
    if( p->rc==SQLITE_OK && p->eStage==OTA_STAGE_OAL ){
      p->rc = sqlite3_exec(p->db, "COMMIT", 0, 0, &p->zErrmsg);
    }

    /* Close the open database handle and VFS object. */

    sqlite3_close(p->db);
    otaDeleteVfs(p);
    sqlite3_free(p->aBuf);
    sqlite3_free(p->aFrame);

    otaEditErrmsg(p);
    rc = p->rc;
    *pzErrmsg = p->zErrmsg;
    sqlite3_free(p);
  }else{
    rc = SQLITE_NOMEM;
................................................................................
  /* Free the contents of the apShm[] array. And the array itself. */
  for(i=0; i<p->nShm; i++){
    sqlite3_free(p->apShm[i]);
  }
  sqlite3_free(p->apShm);
  p->apShm = 0;
  sqlite3_free(p->zDel);

  if( p->openFlags & SQLITE_OPEN_MAIN_DB ){
    ota_file **pp;
    sqlite3_mutex_enter(p->pOtaVfs->mutex);
    for(pp=&p->pOtaVfs->pMain; *pp!=p; pp=&((*pp)->pMainNext));
    *pp = p->pMainNext;
    sqlite3_mutex_leave(p->pOtaVfs->mutex);
  }

  /* Close the underlying file handle */
  rc = p->pReal->pMethods->xClose(p->pReal);
  return rc;
}


/*
** Read and return an unsigned 32-bit big-endian integer from the buffer 
** passed as the only argument.
*/
static u32 otaGetU32(u8 *aBuf){
  return ((u32)aBuf[0] << 24)
       + ((u32)aBuf[1] << 16)
       + ((u32)aBuf[2] <<  8)
       + ((u32)aBuf[3]);
}

/*
** Read data from an otaVfs-file.
*/
static int otaVfsRead(
  sqlite3_file *pFile, 
  void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  ota_file *p = (ota_file*)pFile;
  int rc;

  if( p->pOta 
   && p->pOta->eStage==OTA_STAGE_CAPTURE
   && (p->openFlags & SQLITE_OPEN_WAL) 
  ){
    rc = otaCaptureWalRead(p->pOta, iOfst, iAmt);
  }else{
    rc = p->pReal->pMethods->xRead(p->pReal, zBuf, iAmt, iOfst);
    if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
      /* These look like magic numbers. But they are stable, as they are part
       ** of the definition of the SQLite file format, which may not change. */

      u8 *pBuf = (u8*)zBuf;
      p->iCookie = otaGetU32(&pBuf[24]);
      p->iWriteVer = pBuf[19];
    }
  }
  return rc;
}

/*
** Write data to an otaVfs-file.
*/
................................................................................
static int otaVfsWrite(
  sqlite3_file *pFile, 
  const void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  ota_file *p = (ota_file*)pFile;
  int rc;
  if( p->pOta 
   && p->pOta->eStage==OTA_STAGE_CAPTURE
   && (p->openFlags & SQLITE_OPEN_MAIN_DB)
  ){
    rc = otaCaptureDbWrite(p->pOta, iOfst);
  }else{
    rc = p->pReal->pMethods->xWrite(p->pReal, zBuf, iAmt, iOfst);
    if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
      /* These look like magic numbers. But they are stable, as they are part
      ** of the definition of the SQLite file format, which may not change. */

      u8 *pBuf = (u8*)zBuf;
      p->iCookie = otaGetU32(&pBuf[24]);
      p->iWriteVer = pBuf[19];
    }
  }
  return rc;
}

/*
** Truncate an otaVfs-file.
*/
................................................................................
}

/*
** Sync an otaVfs-file.
*/
static int otaVfsSync(sqlite3_file *pFile, int flags){
  ota_file *p = (ota_file *)pFile;
  if( p->pOta && p->pOta->eStage==OTA_STAGE_CAPTURE ){
    if( p->openFlags & SQLITE_OPEN_MAIN_DB ){
      return SQLITE_INTERNAL;
    }
    return SQLITE_OK;
  }
  return p->pReal->pMethods->xSync(p->pReal, flags);
}

/*
** Return the current file-size of an otaVfs-file.
*/
static int otaVfsFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
................................................................................
** Lock an otaVfs-file.
*/
static int otaVfsLock(sqlite3_file *pFile, int eLock){
  ota_file *p = (ota_file*)pFile;
  sqlite3ota *pOta = p->pOta;
  int rc = SQLITE_OK;

  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( pOta && eLock==SQLITE_LOCK_EXCLUSIVE && pOta->eStage!=OTA_STAGE_DONE ){

    /* Do not allow EXCLUSIVE locks. Preventing SQLite from taking this 
    ** prevents it from checkpointing the database from sqlite3_close(). */
    rc = SQLITE_BUSY;
  }else{
    rc = p->pReal->pMethods->xLock(p->pReal, eLock);
  }

................................................................................
/*
** File control method. For custom operations on an otaVfs-file.
*/
static int otaVfsFileControl(sqlite3_file *pFile, int op, void *pArg){
  ota_file *p = (ota_file *)pFile;
  int (*xControl)(sqlite3_file*,int,void*) = p->pReal->pMethods->xFileControl;

  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( op==SQLITE_FCNTL_OTA ){
    int rc;
    sqlite3ota *pOta = (sqlite3ota*)pArg;

    /* First try to find another OTA vfs lower down in the vfs stack. If
    ** one is found, this vfs will operate in pass-through mode. The lower
    ** level vfs will do the special OTA handling.  */
................................................................................
      rc = xControl(p->pReal, SQLITE_FCNTL_ZIPVFS_PAGER, &dummy);
      if( rc==SQLITE_OK ){
        rc = SQLITE_ERROR;
        pOta->zErrmsg = sqlite3_mprintf("ota/zipvfs setup error");
      }else if( rc==SQLITE_NOTFOUND ){
        pOta->pTargetFd = p;
        p->pOta = pOta;
        if( p->pWalFd ) p->pWalFd->pOta = pOta;
        rc = SQLITE_OK;
      }
    }
    return rc;
  }
  return xControl(p->pReal, op, pArg);
}
................................................................................
}

/*
** Shared-memory methods are all pass-thrus.
*/
static int otaVfsShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  ota_file *p = (ota_file*)pFile;
  sqlite3ota *pOta = p->pOta;
  int rc = SQLITE_OK;

#ifdef SQLITE_AMALGAMATION
    assert( WAL_CKPT_LOCK==1 );
#endif

  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( pOta && pOta->eStage==OTA_STAGE_OAL ){
    /* Magic number 1 is the WAL_CKPT_LOCK lock. Preventing SQLite from
    ** taking this lock also prevents any checkpoints from occurring. 
    ** todo: really, it's not clear why this might occur, as 
    ** wal_autocheckpoint ought to be turned off.  */
    if( ofst==WAL_LOCK_CKPT && n==1 ) rc = SQLITE_BUSY;
  }else{
    int bCapture = 0;
    if( n==1 && (flags & SQLITE_SHM_EXCLUSIVE)
     && p->pOta && p->pOta->eStage==OTA_STAGE_CAPTURE
     && (ofst==WAL_LOCK_WRITE || ofst==WAL_LOCK_CKPT || ofst==WAL_LOCK_READ0)
    ){
      bCapture = 1;
    }

    if( bCapture==0 || 0==(flags & SQLITE_SHM_UNLOCK) ){
      rc = p->pReal->pMethods->xShmLock(p->pReal, ofst, n, flags);
      if( bCapture && rc==SQLITE_OK ){
        p->pOta->mLock |= (1 << ofst);
      }
    }
  }

  return rc;
}

static int otaVfsShmMap(
  sqlite3_file *pFile, 
................................................................................
){
  ota_file *p = (ota_file*)pFile;
  int rc = SQLITE_OK;

  /* If not in OTA_STAGE_OAL, allow this call to pass through. Or, if this
  ** ota is in the OTA_STAGE_OAL state, use heap memory for *-shm space 
  ** instead of a file on disk.  */
  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( p->pOta && p->pOta->eStage==OTA_STAGE_OAL ){
    if( iRegion<=p->nShm ){
      int nByte = (iRegion+1) * sizeof(char*);
      char **apNew = (char**)sqlite3_realloc(p->apShm, nByte);
      if( apNew==0 ){
        rc = SQLITE_NOMEM;
      }else{
................................................................................
  p->pReal->pMethods->xShmBarrier(p->pReal);
}

static int otaVfsShmUnmap(sqlite3_file *pFile, int delFlag){
  ota_file *p = (ota_file*)pFile;
  int rc = SQLITE_OK;

  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( p->pOta && p->pOta->eStage==OTA_STAGE_OAL ){
    /* no-op */
  }else{
    rc = p->pReal->pMethods->xShmUnmap(p->pReal, delFlag);
  }
  return rc;
}

static ota_file *otaFindMaindb(ota_vfs *pOtaVfs, const char *zWal){
  ota_file *pDb;
  sqlite3_mutex_enter(pOtaVfs->mutex);
  for(pDb=pOtaVfs->pMain; pDb && pDb->zWal!=zWal; pDb=pDb->pMainNext);
  sqlite3_mutex_leave(pOtaVfs->mutex);
  return pDb;
}

/*
** Open an ota file handle.
*/
static int otaVfsOpen(
  sqlite3_vfs *pVfs,
  const char *zName,
................................................................................
        z += 2;
      }else{
        while( *z==0 ) z++;
      }
      z += (n + 8 + 1);
      pFd->zWal = z;
    }
    else if( flags & SQLITE_OPEN_WAL ){
      ota_file *pDb = otaFindMaindb(pOtaVfs, zName);
      if( pDb ){
        if( pDb->pOta && pDb->pOta->eStage==OTA_STAGE_OAL ){
          char *zCopy = otaStrndup(zName, -1, &rc);
          if( zCopy ){
            int nCopy = strlen(zCopy);
            zCopy[nCopy-3] = 'o';
            zOpen = (const char*)(pFd->zDel = zCopy);
          }
          pFd->pOta = pDb->pOta;
        }
        pDb->pWalFd = pFd;
      }
    }
  }

  if( rc==SQLITE_OK ){
    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, flags, pOutFlags);
  }
  if( pFd->pReal->pMethods ){
    /* The xOpen() operation has succeeded. Set the sqlite3_file.pMethods
    ** pointer and, if the file is a main database file, link it into the
    ** mutex protected linked list of all such files.  */
    pFile->pMethods = &otavfs_io_methods;
    if( flags & SQLITE_OPEN_MAIN_DB ){
      sqlite3_mutex_enter(pOtaVfs->mutex);
      pFd->pMainNext = pOtaVfs->pMain;
      pOtaVfs->pMain = pFd;
      sqlite3_mutex_leave(pOtaVfs->mutex);
    }
  }

  return rc;
}

/*
** Delete the file located at zPath.
................................................................................
){
  ota_vfs *pOtaVfs = (ota_vfs*)pVfs;
  sqlite3_vfs *pRealVfs = pOtaVfs->pRealVfs;
  int rc;

  rc = pRealVfs->xAccess(pRealVfs, zPath, flags, pResOut);

  /* If this call is to check if a *-wal file associated with an OTA target
  ** database connection exists, and the OTA update is in OTA_STAGE_OAL,
  ** the following special handling is activated:
  **
  **   a) if the *-wal file does exist, return SQLITE_CANTOPEN. This
  **      ensures that the OTA extension never tries to update a database
  **      in wal mode, even if the first page of the database file has
  **      been damaged. 
  **
  **   b) if the *-wal file does not exist, claim that it does anyway,
  **      causing SQLite to call xOpen() to open it. This call will also
  **      be intercepted (see the otaVfsOpen() function) and the *-oal
  **      file opened instead.
  */
  if( rc==SQLITE_OK && flags==SQLITE_ACCESS_EXISTS ){
    ota_file *pDb = otaFindMaindb(pOtaVfs, zPath);
    if( pDb && pDb->pOta && pDb->pOta->eStage==OTA_STAGE_OAL ){
      if( *pResOut ){
        rc = SQLITE_CANTOPEN;
      }else{
        *pResOut = 1;
      }
    }
  }

  return rc;
}

/*

  }
  rc = sqlite3ApiExit(db, rc);
  sqlite3_mutex_leave(db->mutex);
  return rc;
#endif
}

#ifdef SQLITE_ENABLE_OTA
/*
** Open an incremental checkpoint handle.
*/
int sqlite3_ckpt_open(
  sqlite3 *db, 
  unsigned char *a, int n, 
  sqlite3_ckpt **ppCkpt
){
  Pager *pPager = 0;
  int rc;

  *ppCkpt = 0;
  sqlite3_mutex_enter(db->mutex);

  /* Find the Pager object. */
  rc = sqlite3_file_control(db,"main",SQLITE_FCNTL_ZIPVFS_PAGER,(void*)&pPager);
  if( rc!=SQLITE_OK ){
    pPager = sqlite3BtreePager(db->aDb[0].pBt);
  }

  rc = sqlite3PagerWalCheckpointStart(db, pPager, a, n, ppCkpt);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}
#endif /* SQLITE_ENABLE_OTA */


/*
** Checkpoint database zDb. If zDb is NULL, or if the buffer zDb points
** to contains a zero-length string, all attached databases are 
** checkpointed.
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb){

  }
  rc = sqlite3ApiExit(db, rc);
  sqlite3_mutex_leave(db->mutex);
  return rc;
#endif
}





























/*
** Checkpoint database zDb. If zDb is NULL, or if the buffer zDb points
** to contains a zero-length string, all attached databases are 
** checkpointed.
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb){

      }
    }

    /* If there is a WAL file in the file-system, open this database in WAL
    ** mode. Otherwise, the following function call is a no-op.
    */
    rc = pagerOpenWalIfPresent(pPager);

#ifndef SQLITE_OMIT_WAL
    assert( pPager->pWal==0 || rc==SQLITE_OK );
#endif
  }

  if( pagerUseWal(pPager) ){
    assert( rc==SQLITE_OK );
................................................................................
*/
int sqlite3PagerWalFramesize(Pager *pPager){
  assert( pPager->eState>=PAGER_READER );
  return sqlite3WalFramesize(pPager->pWal);
}
#endif

#ifdef SQLITE_ENABLE_OTA

/*
** Open an incremental checkpoint handle.
*/
int sqlite3PagerWalCheckpointStart(
  sqlite3 *db, 
  Pager *pPager,
  u8 *a, int n, 
  sqlite3_ckpt **ppCkpt
){
  if( pPager->pWal==0 ){
    *ppCkpt = 0;
    return SQLITE_OK;
  }else{
    return sqlite3WalCheckpointStart(db, pPager->pWal, a, n,
        pPager->xBusyHandler, pPager->pBusyHandlerArg,
        pPager->ckptSyncFlags, ppCkpt
    );
  }
}
#endif /* !SQLITE_ENABLE_OTA */

#endif /* SQLITE_OMIT_DISKIO */

      }
    }

    /* If there is a WAL file in the file-system, open this database in WAL
    ** mode. Otherwise, the following function call is a no-op.
    */
    rc = pagerOpenWalIfPresent(pPager);

#ifndef SQLITE_OMIT_WAL
    assert( pPager->pWal==0 || rc==SQLITE_OK );
#endif
  }

  if( pagerUseWal(pPager) ){
    assert( rc==SQLITE_OK );
................................................................................
*/
int sqlite3PagerWalFramesize(Pager *pPager){
  assert( pPager->eState>=PAGER_READER );
  return sqlite3WalFramesize(pPager->pWal);
}
#endif
























#endif /* SQLITE_OMIT_DISKIO */

  void disable_simulated_io_errors(void);
  void enable_simulated_io_errors(void);
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

int sqlite3PagerWalCheckpointStart(sqlite3*, Pager*, u8*, int, sqlite3_ckpt**);

#endif /* _PAGER_H_ */

  void disable_simulated_io_errors(void);
  void enable_simulated_io_errors(void);
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif



#endif /* _PAGER_H_ */

** ^Zero all [sqlite3_stmt_scanstatus()] related event counters.
**
** This API is only available if the library is built with pre-processor
** symbol [SQLITE_ENABLE_STMT_SCANSTATUS] defined.
*/
SQLITE_EXPERIMENTAL void sqlite3_stmt_scanstatus_reset(sqlite3_stmt*);

/*
** Incremental checkpoint API.
**
** An incremental checkpoint handle is opened using the sqlite3_ckpt_open()
** API. To begin a new checkpoint, the second and third arguments should both
** be passed zero. To resume an earlier checkpoint, the second and third
** arguments should specify a buffer returned by an earlier call to
** sqlite3_ckpt_close(). When resuming a checkpoint, if the database or WAL 
** file has been modified since the checkpoint was suspended, the 
** sqlite3_ckpt_open() call fails with SQLITE_MISMATCH.
**
** Each time sqlite3_ckpt_step() is called on an open checkpoint handle, a
** single page is copied from the WAL file to the database. If no error 
** occurs, but the checkpoint is not finished, SQLITE_OK is returned. If the
** checkpoint has been finished (and so sqlite3_ckpt_step() should not be
** called again), SQLITE_DONE is returned. Otherwise, if an error occurs,
** some other SQLite error code is returned.
**
** Calling sqlite3_ckpt_close() closes an open checkpoint handle. If the
** checkpoint has finished and no error has occurred, SQLITE_OK is returned
** and the two output parameters zeroed. Or, if an error has occurred, an
** error code is returned and the two output parameters are zeroed. Finally,
** if the checkpoint is not finished but no error has occurred, SQLITE_OK is
** returned and the first output variable set to point to a buffer allocated 
** using sqlite3_malloc() containing the serialized state of the checkpoint. 
** The contents of this buffer may be passed to a later call to
** sqlite3_ckpt_open() to restart the checkpoint. The second output variable 
** is set to the size of the buffer in bytes.
**
** These APIs are only available if SQLITE_ENABLE_OTA is defined at compile
** time. They are intended for use by the OTA extension only. As such, they 
** are subject to change or removal at any point.
*/
typedef struct sqlite3_ckpt sqlite3_ckpt;
int sqlite3_ckpt_open(sqlite3*, unsigned char*, int n, sqlite3_ckpt **ppCkpt);
int sqlite3_ckpt_step(sqlite3_ckpt*);
int sqlite3_ckpt_close(sqlite3_ckpt*, unsigned char **pa, int *pn);

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */

** ^Zero all [sqlite3_stmt_scanstatus()] related event counters.
**
** This API is only available if the library is built with pre-processor
** symbol [SQLITE_ENABLE_STMT_SCANSTATUS] defined.
*/
SQLITE_EXPERIMENTAL void sqlite3_stmt_scanstatus_reset(sqlite3_stmt*);







































/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */

    ht_slot *aIndex;              /* i0, i1, i2... such that aPgno[iN] ascend */
    u32 *aPgno;                   /* Array of page numbers. */
    int nEntry;                   /* Nr. of entries in aPgno[] and aIndex[] */
    int iZero;                    /* Frame number associated with aPgno[0] */
  } aSegment[1];                  /* One for every 32KB page in the wal-index */
};

/*
** An object of the following type is used to store state information for
** an ongoing checkpoint operation. For normal checkpoints, the instance 
** is allocated on the stack by the walCheckpoint() function. For the special
** incremental checkpoints performed by OTA clients, it is allocated in
** heap memory by sqlite3WalCheckpointStart().
**
** See the implementations of walCheckpointStart(), walCheckpointStep() and 
** walCheckpointFinalize() for further details.
*/
typedef struct WalCkpt WalCkpt;
struct WalCkpt {
  sqlite3 *db;                    /* Database pointer (incremental only) */
  int szPage;                     /* Database page-size */
  int sync_flags;                 /* Flags for OsSync() (or 0) */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  u32 mxPage;                     /* Max database page to write */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */
  WalIterator *pIter;             /* Wal iterator context */
  Wal *pWal;                      /* Pointer to owner object */                 
  u8 *aBuf;                       /* Temporary page-sized buffer to use */
  int rc;                         /* Error code. SQLITE_DONE -> finished */
  int nStep;                      /* Number of times pIter has been stepped */
};

/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
................................................................................
      p->aSegment[i].aPgno = (u32 *)aPgno;
    }
  }
  sqlite3_free(aTmp);

  if( rc!=SQLITE_OK ){
    walIteratorFree(p);
    p = 0;
  }
  *pp = p;
  return rc;
}

/*
** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and
................................................................................
** The cache of the wal-index header must be valid to call this function.
** Return the page-size in bytes used by the database.
*/
static int walPagesize(Wal *pWal){
  return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
}

/*
** Initialize the contents of the WalCkpt object indicated by the final
** argument and begin a checkpoint operation. The CKPT lock must already
** be held when this function is called.
**
** Return SQLITE_OK if successful or an error code otherwise.
*/
static int walCheckpointStart(
  Wal *pWal,                      /* Wal connection */
  u8 *aBuf,                       /* Page-sized temporary buffer */
  int nBuf,                       /* Size of aBuf[] in bytes */
  int (*xBusy)(void*),            /* Function to call when busy (or NULL) */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags for OsSync() (or 0) */
  WalCkpt *p                      /* Allocated object to populate */
){
  int rc;                         /* Return code */
  int i;                          /* Iterator variable */

  memset(p, 0, sizeof(WalCkpt));
  if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
    return SQLITE_CORRUPT_BKPT;
  }

  p->szPage = walPagesize(pWal);
  p->pWal = pWal;
  p->aBuf = aBuf;
  p->sync_flags = sync_flags;
  testcase( p->szPage<=32768 );
  testcase( p->szPage>=65536 );
  p->pInfo = walCkptInfo(pWal);
  if( p->pInfo->nBackfill>=pWal->hdr.mxFrame ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &p->pIter);
  if( rc!=SQLITE_OK ) return rc;
  assert( p->pIter );

  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  p->mxSafeFrame = pWal->hdr.mxFrame;
  p->mxPage = pWal->hdr.nPage;
  for(i=1; i<WAL_NREADER; i++){
    u32 y = p->pInfo->aReadMark[i];
    if( p->mxSafeFrame>y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        p->pInfo->aReadMark[i] = (i==1 ? p->mxSafeFrame : READMARK_NOT_USED);
        walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
      }else if( rc==SQLITE_BUSY ){
        p->mxSafeFrame = y;
        xBusy = 0;
      }else{
        walIteratorFree(p->pIter);
        p->pIter = 0;
        return rc;
      }
    }
  }

  if( p->pInfo->nBackfill>=p->mxSafeFrame
   || (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0), 1))!=SQLITE_OK
  ){
    walIteratorFree(p->pIter);
    p->pIter = 0;
  }
  if( rc==SQLITE_BUSY ) rc = SQLITE_OK;

  if( rc==SQLITE_OK && p->pIter ){
    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }

    /* If the database may grow as a result of this checkpoint, hint
    ** about the eventual size of the db file to the VFS layer.  */
    if( rc==SQLITE_OK ){
      i64 nSize;                  /* Current size of database file */
      i64 nReq = ((i64)p->mxPage * p->szPage);
      rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
      if( rc==SQLITE_OK && nSize<nReq ){
        sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq);
      }
    }
  }

  return rc;
}

/*
** Attempt to copy the next frame from the wal file to the database file. If
** there are no more frames to copy to the database file return SQLITE_DONE.
** If the frame is successfully copied, return SQLITE_OK. Or, if an error
** occurs, return an SQLite error code.
*/
static int walCheckpointStep(WalCkpt *p){
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  int rc = SQLITE_DONE;

  assert( p->rc==SQLITE_OK );
  while( p->pIter && 0==walIteratorNext(p->pIter, &iDbpage, &iFrame) ){
    i64 iOffset;
    assert( walFramePgno(p->pWal, iFrame)==iDbpage );
    p->nStep++;
    if( iFrame<=p->pInfo->nBackfill 
     || iFrame>p->mxSafeFrame 
     || iDbpage>p->mxPage 
    ){
      continue;
    }

    iOffset = walFrameOffset(iFrame, p->szPage) + WAL_FRAME_HDRSIZE;
    /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
    rc = sqlite3OsRead(p->pWal->pWalFd, p->aBuf, p->szPage, iOffset);
    if( rc!=SQLITE_OK ) break;
    iOffset = (iDbpage-1)*(i64)p->szPage;
    testcase( IS_BIG_INT(iOffset) );
    rc = sqlite3OsWrite(p->pWal->pDbFd, p->aBuf, p->szPage, iOffset);
    break;
  }

  p->rc = rc;
  return rc;
}

/*
** The current round of checkpointing work using the object indicated by
** the only argument is now finished. If no error occcurred, this function
** saves the results to shared memory (i.e. updates the WalCkptInfo.nBackfill
** variable), and truncates and syncs the database file as required.
**
** All dynamic resources currently held by the WalCkpt object are released. 
** It is the responsibility of the caller to delete the WalCkpt itself if
** required.
*/
static int walCheckpointFinalize(WalCkpt *p){
  if( p->pIter ){
    int rc = p->rc;
    Wal *pWal = p->pWal;

    if( rc==SQLITE_DONE ){
      /* If work was completed */
      rc = SQLITE_OK;
      if( p->mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
        i64 szDb = pWal->hdr.nPage*(i64)p->szPage;
        testcase( IS_BIG_INT(szDb) );
        rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
        if( rc==SQLITE_OK && p->sync_flags ){
          rc = sqlite3OsSync(pWal->pDbFd, p->sync_flags);
        }
      }
      if( rc==SQLITE_OK ){
        p->pInfo->nBackfill = p->mxSafeFrame;
      }
      p->rc = rc;
    }else{
#ifdef SQLITE_ENABLE_OTA
      if( rc==SQLITE_OK && p->sync_flags ){
        /* If work was not completed, but no error has occured. */
        p->rc = sqlite3OsSync(pWal->pDbFd, p->sync_flags);
      }
#else
      assert( rc!=SQLITE_OK );
#endif
    }

    /* Release the reader lock held while backfilling */
    walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1);
    walIteratorFree(p->pIter);
    p->pIter = 0;
  }else if( p->rc==SQLITE_DONE ){
    p->rc = SQLITE_OK;
  }

  return p->rc;
}

/*
** The following is guaranteed when this function is called:
**
**   a) the WRITER lock is held,
**   b) the entire log file has been checkpointed, and
**   c) any existing readers are reading exclusively from the database
**      file - there are no readers that may attempt to read a frame from
................................................................................
*/
static int walCheckpoint(
  Wal *pWal,                      /* Wal connection */
  int eMode,                      /* One of PASSIVE, FULL or RESTART */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags for OsSync() (or 0) */
  u8 *zBuf,                       /* Temporary buffer to use */
  int nBuf                        /* Size of zBuf in bytes */
){







  int rc;                         /* Return code */
  WalCkpt sC;















  /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
  ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
  assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );

  rc = walCheckpointStart(pWal, zBuf, nBuf, xBusy, pBusyArg, sync_flags, &sC);



















  if( rc!=SQLITE_OK ) goto walcheckpoint_out;

  /* Step the checkpoint object until it reports something other than 

































































  ** SQLITE_OK.  */
  while( SQLITE_OK==(rc = walCheckpointStep(&sC)) );
  rc = walCheckpointFinalize(&sC);



  /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
  ** entire wal file has been copied into the database file, then block 
  ** until all readers have finished using the wal file. This ensures that 
  ** the next process to write to the database restarts the wal file.
  */
  if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
    assert( pWal->writeLock );
    if( sC.pInfo->nBackfill<pWal->hdr.mxFrame ){
      rc = SQLITE_BUSY;
    }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
      u32 salt1;
      sqlite3_randomness(4, &salt1);
      assert( sC.pInfo->nBackfill==pWal->hdr.mxFrame );
      rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
      if( rc==SQLITE_OK ){
        if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
          /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
          ** SQLITE_CHECKPOINT_RESTART with the addition that it also
          ** truncates the log file to zero bytes just prior to a
          ** successful return.
................................................................................
        }
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }
    }
  }

 walcheckpoint_out:
  walIteratorFree(sC.pIter);
  return rc;
}

/*
** If the WAL file is currently larger than nMax bytes in size, truncate
** it to exactly nMax bytes. If an error occurs while doing so, ignore it.
*/
................................................................................
  if( rx ){
    sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
  }
}

/*
** Close a connection to a log file.
**
** If parameter zBuf is not NULL, also attempt to obtain an exclusive 
** lock and run a checkpoint.
*/
int sqlite3WalClose(
  Wal *pWal,                      /* Wal to close */
  int sync_flags,                 /* Flags to pass to OsSync() (or 0) */
  int nBuf,
  u8 *zBuf                        /* Buffer of at least nBuf bytes */
){
................................................................................
    ** ordinary, rollback-mode locking methods, this guarantees that the
    ** connection associated with this log file is the only connection to
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
#ifdef SQLITE_ENABLE_OTA
    if( zBuf )          /* In non-OTA builds, zBuf is always non-NULL */
#endif
    {
      rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
      if( rc==SQLITE_OK ){
        if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
          pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
        }
        rc = sqlite3WalCheckpoint(
            pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
        );
        if( rc==SQLITE_OK ){
          int bPersist = -1;
          sqlite3OsFileControlHint(
              pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
          );
          if( bPersist!=1 ){
            /* Try to delete the WAL file if the checkpoint completed and
            ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal
            ** mode (!bPersist) */
            isDelete = 1;
          }else if( pWal->mxWalSize>=0 ){
            /* Try to truncate the WAL file to zero bytes if the checkpoint
            ** completed and fsynced (rc==SQLITE_OK) and we are in persistent
            ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
            ** non-negative value (pWal->mxWalSize>=0).  Note that we truncate
            ** to zero bytes as truncating to the journal_size_limit might
            ** leave a corrupt WAL file on disk. */
            walLimitSize(pWal, 0);
          }
        }
      }
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
................................................................................
    if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
      sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
    }
  }

  /* Copy data from the log to the database file. */
  if( rc==SQLITE_OK ){



    rc = walCheckpoint(pWal, eMode2, xBusy2, pBusyArg, sync_flags, zBuf, nBuf);


    /* If no error occurred, set the output variables. */
    if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
      if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
      if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
    }
  }
................................................................................
  sqlite3WalEndWriteTransaction(pWal);
  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
  return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc);
}

#ifdef SQLITE_ENABLE_OTA

/*
** Step the checkpoint object passed as the first argument.
*/
int sqlite3_ckpt_step(sqlite3_ckpt *pCkpt){
  int rc;
  WalCkpt *p = (WalCkpt*)pCkpt;
  sqlite3_mutex_enter(p->db->mutex);
  rc = walCheckpointStep(p);
  sqlite3_mutex_leave(p->db->mutex);
  return rc;
}

/*
** Close the checkpoint object passed as the first argument. If the checkpoint
** was completed, zero the two output variables. Otherwise, set *paState to
** point to a buffer containing data that may be passed to a subsequent 
** call to ckpt_open() to resume the checkpoint. In this case *pnState is
** set to the size of the buffer in bytes. The buffer should be eventually
** freed by the caller using sqlite3_free().
*/
int sqlite3_ckpt_close(sqlite3_ckpt *pCkpt, u8 **paState, int *pnState){
  int rc;
  WalCkpt *p = (WalCkpt*)pCkpt;
  sqlite3 *db = p->db;
  Wal *pWal = p->pWal;
  sqlite3_mutex_enter(db->mutex);
  if( paState ){
    *paState = 0;
    *pnState = 0;
    if( p->rc==SQLITE_OK ){
      u8 *aState = sqlite3_malloc(sizeof(u32) * 3);
      if( aState==0 ){
        p->rc = SQLITE_NOMEM;
      }else{
        *pnState = sizeof(u32)*3;
        sqlite3Put4byte(&aState[0], p->nStep);
        sqlite3Put4byte(&aState[4], p->pWal->hdr.aCksum[0]);
        sqlite3Put4byte(&aState[8], p->pWal->hdr.aCksum[1]);
        *paState = aState;
      }
    }
  }
  rc = walCheckpointFinalize(p);
  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  sqlite3_free(p);
  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

/*
** Open an incremental checkpoint handle.
*/
int sqlite3WalCheckpointStart(
  sqlite3 *db,                    /* Database connection */
  Wal *pWal,                      /* Wal connection */
  u8 *aState, int nState,         /* Checkpoint state to restore */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  sqlite3_ckpt **ppCkpt           /* OUT: Incremental checkpoint object */
){
  WalCkpt *p = 0;
  int isChanged = 0;
  int rc;
  int pgsz;

  *ppCkpt = 0;
  if( pWal->readOnly ) return SQLITE_READONLY;
  WALTRACE(("WAL%p: checkpoint begins\n", pWal));
  rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
  if( rc ){
    /* Usually this is SQLITE_BUSY meaning that another thread or process
    ** is already running a checkpoint, or maybe a recovery.  But it might
    ** also be SQLITE_IOERR. */
    return rc;
  }
  pWal->ckptLock = 1;

  /* Read the wal-index header. */
  rc = walIndexReadHdr(pWal, &isChanged);
  if( rc!=SQLITE_OK ) goto ckptstart_out;
  if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
    sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
  }

  pgsz = walPagesize(pWal);
  p = sqlite3_malloc(sizeof(WalCkpt) + pgsz);
  if( p==0 ){
    rc = SQLITE_NOMEM;
    goto ckptstart_out;
  }

  rc = walCheckpointStart(
      pWal, (u8*)&p[1], pgsz, xBusy, pBusyArg, sync_flags, p
  );
  p->db = db;

  if( rc==SQLITE_OK && aState ){
    if( nState!=sizeof(u32)*3 ){
      rc = SQLITE_CORRUPT_BKPT;
    }else{
      int i;
      if( pWal->hdr.aCksum[0]!=sqlite3Get4byte(&aState[4])
       || pWal->hdr.aCksum[1]!=sqlite3Get4byte(&aState[8])
      ){
        rc = SQLITE_MISMATCH;
      }else{
        p->nStep = (int)sqlite3Get4byte(aState);
        sqlite3Put4byte(&aState[4], pWal->hdr.aCksum[0]);
        sqlite3Put4byte(&aState[8], pWal->hdr.aCksum[1]);
        for(i=0; rc==SQLITE_OK && i<p->nStep; i++){
          u32 dummy1, dummy2; 
          rc = walIteratorNext(p->pIter, &dummy1, &dummy2);
        }
      }
    }
  }

 ckptstart_out:
  if( rc!=SQLITE_OK ){
    if( p ) walIteratorFree(p->pIter);
    walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
    pWal->ckptLock = 0;
    sqlite3_free(p);
    p = 0;
  }
  *ppCkpt = (sqlite3_ckpt*)p;
  return rc;
}
#endif /* SQLITE_ENABLE_OTA */

/*
** Unless the wal file is empty, check that the 8 bytes of salt stored in
** the wal header are identical to those in the buffer indicated by the
** second argument. If they are not, return SQLITE_BUSY_SNAPSHOT. Otherwise,
** if the buffers match or the WAL file is empty, return SQLITE_OK.
*/
int sqlite3WalCheckSalt(Wal *pWal, sqlite3_file *pFd){
  int rc = SQLITE_OK;
  if( pWal->hdr.mxFrame>0 ){
    u8 aData[16];
    rc = sqlite3OsRead(pFd, aData, sizeof(aData), 24);
    if( rc==SQLITE_OK && memcmp(pWal->hdr.aSalt, aData, 8) ){
      rc = SQLITE_BUSY_SNAPSHOT;
    }
  }
  return rc;
}

/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called.  If no commits have occurred since
** the last call, then return 0.
*/
int sqlite3WalCallback(Wal *pWal){
  u32 ret = 0;

    ht_slot *aIndex;              /* i0, i1, i2... such that aPgno[iN] ascend */
    u32 *aPgno;                   /* Array of page numbers. */
    int nEntry;                   /* Nr. of entries in aPgno[] and aIndex[] */
    int iZero;                    /* Frame number associated with aPgno[0] */
  } aSegment[1];                  /* One for every 32KB page in the wal-index */
};


























/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
................................................................................
      p->aSegment[i].aPgno = (u32 *)aPgno;
    }
  }
  sqlite3_free(aTmp);

  if( rc!=SQLITE_OK ){
    walIteratorFree(p);

  }
  *pp = p;
  return rc;
}

/*
** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and
................................................................................
** The cache of the wal-index header must be valid to call this function.
** Return the page-size in bytes used by the database.
*/
static int walPagesize(Wal *pWal){
  return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
}























































































































































































/*
** The following is guaranteed when this function is called:
**
**   a) the WRITER lock is held,
**   b) the entire log file has been checkpointed, and
**   c) any existing readers are reading exclusively from the database
**      file - there are no readers that may attempt to read a frame from
................................................................................
*/
static int walCheckpoint(
  Wal *pWal,                      /* Wal connection */
  int eMode,                      /* One of PASSIVE, FULL or RESTART */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags for OsSync() (or 0) */

  u8 *zBuf                        /* Temporary buffer to use */
){
  int rc = SQLITE_OK;             /* Return code */
  int szPage;                     /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  u32 mxPage;                     /* Max database page to write */
  int i;                          /* Loop counter */

  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  szPage = walPagesize(pWal);
  testcase( szPage<=32768 );
  testcase( szPage>=65536 );
  pInfo = walCkptInfo(pWal);
  if( pInfo->nBackfill<pWal->hdr.mxFrame ){

    /* Allocate the iterator */
    rc = walIteratorInit(pWal, &pIter);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    assert( pIter );

    /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
    ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
    assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );


    /* Compute in mxSafeFrame the index of the last frame of the WAL that is
    ** safe to write into the database.  Frames beyond mxSafeFrame might
    ** overwrite database pages that are in use by active readers and thus
    ** cannot be backfilled from the WAL.
    */
    mxSafeFrame = pWal->hdr.mxFrame;
    mxPage = pWal->hdr.nPage;
    for(i=1; i<WAL_NREADER; i++){
      u32 y = pInfo->aReadMark[i];
      if( mxSafeFrame>y ){
        assert( y<=pWal->hdr.mxFrame );
        rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          pInfo->aReadMark[i] = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
        }else if( rc==SQLITE_BUSY ){
          mxSafeFrame = y;
          xBusy = 0;
        }else{
          goto walcheckpoint_out;
        }

      }
    }

    if( pInfo->nBackfill<mxSafeFrame
     && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK
    ){
      i64 nSize;                    /* Current size of database file */
      u32 nBackfill = pInfo->nBackfill;

      /* Sync the WAL to disk */
      if( sync_flags ){
        rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
      }

      /* If the database may grow as a result of this checkpoint, hint
      ** about the eventual size of the db file to the VFS layer.
      */
      if( rc==SQLITE_OK ){
        i64 nReq = ((i64)mxPage * szPage);
        rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
        if( rc==SQLITE_OK && nSize<nReq ){
          sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq);
        }
      }


      /* Iterate through the contents of the WAL, copying data to the db file */
      while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
        i64 iOffset;
        assert( walFramePgno(pWal, iFrame)==iDbpage );
        if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){
          continue;
        }
        iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
        /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
        rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
        if( rc!=SQLITE_OK ) break;
        iOffset = (iDbpage-1)*(i64)szPage;
        testcase( IS_BIG_INT(iOffset) );
        rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
        if( rc!=SQLITE_OK ) break;
      }

      /* If work was actually accomplished... */
      if( rc==SQLITE_OK ){
        if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
          i64 szDb = pWal->hdr.nPage*(i64)szPage;
          testcase( IS_BIG_INT(szDb) );
          rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
          if( rc==SQLITE_OK && sync_flags ){
            rc = sqlite3OsSync(pWal->pDbFd, sync_flags);
          }
        }
        if( rc==SQLITE_OK ){
          pInfo->nBackfill = mxSafeFrame;
        }
      }

      /* Release the reader lock held while backfilling */
      walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1);
    }

    if( rc==SQLITE_BUSY ){
      /* Reset the return code so as not to report a checkpoint failure
      ** just because there are active readers.  */
      rc = SQLITE_OK;


    }
  }

  /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
  ** entire wal file has been copied into the database file, then block 
  ** until all readers have finished using the wal file. This ensures that 
  ** the next process to write to the database restarts the wal file.
  */
  if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
    assert( pWal->writeLock );
    if( pInfo->nBackfill<pWal->hdr.mxFrame ){
      rc = SQLITE_BUSY;
    }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
      u32 salt1;
      sqlite3_randomness(4, &salt1);
      assert( pInfo->nBackfill==pWal->hdr.mxFrame );
      rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
      if( rc==SQLITE_OK ){
        if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
          /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
          ** SQLITE_CHECKPOINT_RESTART with the addition that it also
          ** truncates the log file to zero bytes just prior to a
          ** successful return.
................................................................................
        }
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }
    }
  }

 walcheckpoint_out:
  walIteratorFree(pIter);
  return rc;
}

/*
** If the WAL file is currently larger than nMax bytes in size, truncate
** it to exactly nMax bytes. If an error occurs while doing so, ignore it.
*/
................................................................................
  if( rx ){
    sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
  }
}

/*
** Close a connection to a log file.



*/
int sqlite3WalClose(
  Wal *pWal,                      /* Wal to close */
  int sync_flags,                 /* Flags to pass to OsSync() (or 0) */
  int nBuf,
  u8 *zBuf                        /* Buffer of at least nBuf bytes */
){
................................................................................
    ** ordinary, rollback-mode locking methods, this guarantees that the
    ** connection associated with this log file is the only connection to
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */




    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
        pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
      }
      rc = sqlite3WalCheckpoint(
          pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
      );
      if( rc==SQLITE_OK ){
        int bPersist = -1;
        sqlite3OsFileControlHint(
            pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
        );
        if( bPersist!=1 ){
          /* Try to delete the WAL file if the checkpoint completed and
          ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal
          ** mode (!bPersist) */
          isDelete = 1;
        }else if( pWal->mxWalSize>=0 ){
          /* Try to truncate the WAL file to zero bytes if the checkpoint
          ** completed and fsynced (rc==SQLITE_OK) and we are in persistent
          ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
          ** non-negative value (pWal->mxWalSize>=0).  Note that we truncate
          ** to zero bytes as truncating to the journal_size_limit might
          ** leave a corrupt WAL file on disk. */
          walLimitSize(pWal, 0);

        }
      }
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
................................................................................
    if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
      sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
    }
  }

  /* Copy data from the log to the database file. */
  if( rc==SQLITE_OK ){
    if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
      rc = SQLITE_CORRUPT_BKPT;
    }else{
      rc = walCheckpoint(pWal, eMode2, xBusy2, pBusyArg, sync_flags, zBuf);
    }

    /* If no error occurred, set the output variables. */
    if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
      if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
      if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
    }
  }
................................................................................
  sqlite3WalEndWriteTransaction(pWal);
  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
  return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc);
}


























































































































































/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called.  If no commits have occurred since
** the last call, then return 0.
*/
int sqlite3WalCallback(Wal *pWal){
  u32 ret = 0;

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);

int sqlite3WalCheckSalt(Wal *pWal, sqlite3_file*);

int sqlite3WalCheckpointStart(sqlite3 *,
  Wal *pWal,                      /* Wal connection */
  u8 *aState, int nState,         /* Checkpoint state to restore */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  sqlite3_ckpt **ppCkpt           /* OUT: Incremental checkpoint object */
);

#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);












#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */