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
6// +build darwin,!ios linux
7
8package unix
9
10import (
11	"unsafe"
12
13	"golang.org/x/sys/internal/unsafeheader"
14)
15
16// SysvShmAttach attaches the Sysv shared memory segment associated with the
17// shared memory identifier id.
18func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
19	addr, errno := shmat(id, addr, flag)
20	if errno != nil {
21		return nil, errno
22	}
23
24	// Retrieve the size of the shared memory to enable slice creation
25	var info SysvShmDesc
26
27	_, err := SysvShmCtl(id, IPC_STAT, &info)
28	if err != nil {
29		// release the shared memory if we can't find the size
30
31		// ignoring error from shmdt as there's nothing sensible to return here
32		shmdt(addr)
33		return nil, err
34	}
35
36	// Use unsafe to convert addr into a []byte.
37	// TODO: convert to unsafe.Slice once we can assume Go 1.17
38	var b []byte
39	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))
40	hdr.Data = unsafe.Pointer(addr)
41	hdr.Cap = int(info.Segsz)
42	hdr.Len = int(info.Segsz)
43	return b, nil
44}
45
46// SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
47//
48// It is not safe to use the slice after calling this function.
49func SysvShmDetach(data []byte) error {
50	if len(data) == 0 {
51		return EINVAL
52	}
53
54	return shmdt(uintptr(unsafe.Pointer(&data[0])))
55}
56
57// SysvShmGet returns the Sysv shared memory identifier associated with key.
58// If the IPC_CREAT flag is specified a new segment is created.
59func SysvShmGet(key, size, flag int) (id int, err error) {
60	return shmget(key, size, flag)
61}
62