You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: db.go
    path of file: ./repos/buildkit/vendor/go.etcd.io/bbolt
    
    the code of the file until where you have to start completion: package bbolt

import (
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"os"
	"runtime"
	"sort"
	"sync"
	"time"
	"unsafe"
)

// The largest step that can be taken when remapping the mmap.
const maxMmapStep = 1 << 30 // 1GB

// The data file format version.
const version = 2

// Represents a marker value to indicate that a file is a Bolt DB.
const magic uint32 = 0xED0CDAED

const pgidNoFreelist pgid = 0xffffffffffffffff

// IgnoreNoSync specifies whether the NoSync field of a DB is ignored when
// syncing changes to a file.  This is required as some operating systems,
// such as OpenBSD, do not have a unified buffer cache (UBC) and writes
// must be synchronized using the msync(2) syscall.
const IgnoreNoSync = runtime.GOOS == "openbsd"

//
    
func (db *DB) getPageSize() (int, error) {
	var (
		meta0CanRead, meta1CanRead bool
	)

	// Read the first meta page to determine the page size.
	if pgSize, canRead, err := db.getPageSizeFromFirstMeta(); err != nil {
		// We cannot read the page size from page 0, but can read page 0.
		meta0CanRead = canRead
	} else {
		return pgSize, nil
	}

	// Read the second meta page to determine the page size.
	if pgSize, canRead, err := db.getPageSizeFromSecondMeta(); err != nil {
		// We cannot read the page size from page 1, but can read page 1.
		meta1CanRead = canRead
	} else {
		return pgSize, nil
	}

	// If we can't read the page size from both pages, but can read
	// either page, then we assume it's the same as the OS or the one
	// given, since that's how the page size was chosen in the first place.
	//
	// If both pages are invalid, and (this OS uses a different page size
	// from what the database was created with or the given page size is
	// different from what the database was created with), then we are out
	// of luck and cannot access the database.
	if meta0CanRead || meta1CanRead {
		return db.pageSize, nil
	}

	return 0, ErrInvalid
}