1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5//go:build (darwin && !ios) || linux || zos
6
7package unix
8
9import "unsafe"
10
11// SysvShmAttach attaches the Sysv shared memory segment associated with the
12// shared memory identifier id.
13func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
14	addr, errno := shmat(id, addr, flag)
15	if errno != nil {
16		return nil, errno
17	}
18
19	// Retrieve the size of the shared memory to enable slice creation
20	var info SysvShmDesc
21
22	_, err := SysvShmCtl(id, IPC_STAT, &info)
23	if err != nil {
24		// release the shared memory if we can't find the size
25
26		// ignoring error from shmdt as there's nothing sensible to return here
27		shmdt(addr)
28		return nil, err
29	}
30
31	// Use unsafe to convert addr into a []byte.
32	b := unsafe.Slice((*byte)(unsafe.Pointer(addr)), int(info.Segsz))
33	return b, nil
34}
35
36// SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
37//
38// It is not safe to use the slice after calling this function.
39func SysvShmDetach(data []byte) error {
40	if len(data) == 0 {
41		return EINVAL
42	}
43
44	return shmdt(uintptr(unsafe.Pointer(&data[0])))
45}
46
47// SysvShmGet returns the Sysv shared memory identifier associated with key.
48// If the IPC_CREAT flag is specified a new segment is created.
49func SysvShmGet(key, size, flag int) (id int, err error) {
50	return shmget(key, size, flag)
51}
52