//go:build unix

package mem

import (
	"syscall"
	"unsafe"
)

const (
	PERM_NONE    = syscall.PROT_NONE
	PERM_READ    = syscall.PROT_READ
	PERM_WRITE   = syscall.PROT_WRITE
	PERM_EXECUTE = syscall.PROT_EXEC
)

func Reserve(total_address_space uintptr) ([]byte, error) {
	data, err := syscall.Mmap(-1, 0, int(total_address_space), syscall.PROT_NONE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
	if err != nil {
		return nil, err
	}

	return data, nil
}

func Unreserve(reserved []byte) error {
	return syscall.Munmap(reserved)
}

func Commit(reserved []byte, perms int) error {
	return syscall.Mprotect(reserved, perms)
}

func Decommit(committed []byte) (err error) {
	err = syscall.Mprotect(committed, syscall.PROT_NONE)
	if err != nil {
		return
	}

	return madvise(committed, syscall.MADV_DONTNEED)
}

var _zero uintptr

func madvise(b []byte, advice int) (err error) {
	var _p0 unsafe.Pointer
	if len(b) > 0 {
		_p0 = unsafe.Pointer(&b[0])
	} else {
		_p0 = unsafe.Pointer(&_zero)
	}

	_, _, e := syscall.Syscall(syscall.SYS_MADVISE, uintptr(_p0), uintptr(len(b)), uintptr(advice))
	if e != 0 {
		err = syscall.Errno(e)
	}

	return
}