// Copyright 2021 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

//go:build (darwin && !ios) || linux

// +build darwin,!ios linux

package unix

import (

	"unsafe"

	"golang.org/x/sys/internal/unsafeheader"

)

// SysvShmAttach attaches the Sysv shared memory segment associated with the

// shared memory identifier id.

func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {

	addr, errno := shmat(id, addr, flag)

	if errno != nil {

		return nil, errno

	}

	// Retrieve the size of the shared memory to enable slice creation

	var info SysvShmDesc

	_, err := SysvShmCtl(id, IPC_STAT, &info)

	if err != nil {

		// release the shared memory if we can't find the size

		// ignoring error from shmdt as there's nothing sensible to return here

		shmdt(addr)

		return nil, err

	}

	// Use unsafe to convert addr into a []byte.

	// TODO: convert to unsafe.Slice once we can assume Go 1.17

	var b []byte

	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))

	hdr.Data = unsafe.Pointer(addr)

	hdr.Cap = int(info.Segsz)

	hdr.Len = int(info.Segsz)

	return b, nil

}

// SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.

//

// It is not safe to use the slice after calling this function.

func SysvShmDetach(data []byte) error {

	if len(data) == 0 {

		return EINVAL

	}

	return shmdt(uintptr(unsafe.Pointer(&data[0])))

}

// SysvShmGet returns the Sysv shared memory identifier associated with key.

// If the IPC_CREAT flag is specified a new segment is created.

func SysvShmGet(key, size, flag int) (id int, err error) {

	return shmget(key, size, flag)

}