int *pMapSize, 
  void **pp
){
  int rc = SQLITE_OK;
  Testvfs *p = (Testvfs *)(pVfs->pAppData);
  TestvfsShm *pShm = (TestvfsShm *)pShmHandle;

  tvfsGrowBuffer(pShm, reqMapSize, pMapSize);
  tvfsExecTcl(p, "xShmGet", 
      Tcl_NewStringObj(pShm->pBuffer->zFile, -1), pShm->id, 0
  );
  tvfsResultCode(p, &rc);
  if( rc==SQLITE_OK ){

    *pp = pShm->pBuffer->a;
  }
  return rc;
}

static int tvfsShmRelease(sqlite3_vfs *pVfs, sqlite3_shm *pShmHandle){
  int rc = SQLITE_OK;

  int *pMapSize, 
  void **pp
){
  int rc = SQLITE_OK;
  Testvfs *p = (Testvfs *)(pVfs->pAppData);
  TestvfsShm *pShm = (TestvfsShm *)pShmHandle;


  tvfsExecTcl(p, "xShmGet", 
      Tcl_NewStringObj(pShm->pBuffer->zFile, -1), pShm->id, 0
  );
  tvfsResultCode(p, &rc);
  if( rc==SQLITE_OK ){
    tvfsGrowBuffer(pShm, reqMapSize, pMapSize);
    *pp = pShm->pBuffer->a;
  }
  return rc;
}

static int tvfsShmRelease(sqlite3_vfs *pVfs, sqlite3_shm *pShmHandle){
  int rc = SQLITE_OK;

                             &pWal->szWIndex, (void**)(char*)&pWal->pWiData);
    if( rc==SQLITE_OK && pWal->pWiData==0 ){
      /* Make sure pWal->pWiData is not NULL while we are holding the
      ** lock on the mapping. */
      assert( pWal->szWIndex==0 );
      pWal->pWiData = &pWal->iCallback;
    }
    assert( rc==SQLITE_OK || pWal->pWiData==0 );


  }
  return rc;
}

/*
** Remap the wal-index so that the mapping covers the full size
** of the underlying file.
................................................................................
        rc = SQLITE_BUSY;
      }
      walIndexUnmap(pWal);
      if( rc!=SQLITE_OK ){
        walSetLock(pWal, SQLITE_SHM_READ);
      }
    }
  }else if( pWal->lockState==SQLITE_SHM_WRITE ){
    rc = walSetLock(pWal, SQLITE_SHM_READ);
  }
  return rc;
}

/*
** If any data has been written (but not committed) to the log file, this

                             &pWal->szWIndex, (void**)(char*)&pWal->pWiData);
    if( rc==SQLITE_OK && pWal->pWiData==0 ){
      /* Make sure pWal->pWiData is not NULL while we are holding the
      ** lock on the mapping. */
      assert( pWal->szWIndex==0 );
      pWal->pWiData = &pWal->iCallback;
    }
    if( rc!=SQLITE_OK ){
      walIndexUnmap(pWal);
    }
  }
  return rc;
}

/*
** Remap the wal-index so that the mapping covers the full size
** of the underlying file.
................................................................................
        rc = SQLITE_BUSY;
      }
      walIndexUnmap(pWal);
      if( rc!=SQLITE_OK ){
        walSetLock(pWal, SQLITE_SHM_READ);
      }
    }
  }else if( ALWAYS( pWal->lockState==SQLITE_SHM_WRITE ) ){
    rc = walSetLock(pWal, SQLITE_SHM_READ);
  }
  return rc;
}

/*
** If any data has been written (but not committed) to the log file, this

  BEGIN;
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 1 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 2 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 4 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 8 */
  ROLLBACK;
}













































































finish_test

  BEGIN;
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 1 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 2 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 4 */
    INSERT INTO abc SELECT randomblob(900) FROM abc;    /* 8 */
  ROLLBACK;
}

#-------------------------------------------------------------------------
# When a database is checkpointed, SQLite does the following:
#
#   1. xShmLock(CHECKPOINT) to lock the WAL.
#   2. xShmGet(-1) to get a mapping to read the wal-index header.
#   3. If the mapping obtained in (2) is not large enough to cover the
#      entire wal-index, call xShmGet(nReq) to get a larger mapping.
#   4. Do the checkpoint.
#   5. Release the lock and mapping.
#
# This test case tests the outcome of an IO error in step 2.
#
proc shmfault_vfs_cb_6 {method args} {
  switch -- $::shm_state {
    0 { return SQLITE_OK }
    1 {
      if {$method == "xShmGet"} {
        set ::wal_index [tvfs shm [lindex $args 0]]
        tvfs shm [lindex $args 0] [string range $::wal_index 0 65535]
        set ::shm_state 2
      }
    }
    2 {
      if {$method == "xShmGet"} {
        tvfs shm [lindex $args 0] $::wal_index
        return SQLITE_IOERR
      }
    }
  }
  return SQLITE_OK
}
do_test walfault-shm-6.1 {
  set ::shm_state 0
  testvfs tvfs shmfault_vfs_cb_6

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    CREATE TABLE t1(x);
    INSERT INTO t1 VALUES(randomblob(900));
  }
} {wal 0}
do_test walfault-shm-6.2 {
  execsql {
    PRAGMA wal_autocheckpoint = 0;
    BEGIN;
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 2 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 4 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 8 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 16 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 32 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 64 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 128 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 256 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 512 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 1024 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 2048 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 4096 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 8192 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;    /* 16384 */
    COMMIT;
  } db2
} {0}
do_test walfault-shm-6.3 {
  set ::shm_state 1
  catchsql { PRAGMA wal_checkpoint } db2
} {1 {disk I/O error}}
set ::shm_state 0
db close
db2 close
tvfs delete
unset -nocomplain ::wal_index ::shm_state

finish_test