package bolt

import (
	"os"
	"syscall"
	"unsafe"
)

var odirect = syscall.O_DIRECT

// fdatasync flushes written data to a file descriptor.
func fdatasync(f *os.File) error {
	return syscall.Fdatasync(int(f.Fd()))
}

// flock acquires an advisory lock on a file descriptor.
func flock(f *os.File) error {
	return syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
}

// funlock releases an advisory lock on a file descriptor.
func funlock(f *os.File) error {
	return syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
}

// mmap memory maps a DB's data file.
func mmap(db *DB, sz int) error {
	b, err := syscall.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED)
	if err != nil {
		return err
	}

	// Save the original byte slice and convert to a byte array pointer.
	db.dataref = b
	db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
	db.datasz = sz
	return nil
}

// munmap unmaps a DB's data file from memory.
func munmap(db *DB) error {
	// Ignore the unmap if we have no mapped data.
	if db.dataref == nil {
		return nil
	}

	// Unmap using the original byte slice.
	err := syscall.Munmap(db.dataref)
	db.dataref = nil
	db.data = nil
	db.datasz = 0
	return err
}