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 

     8 package unix

     9 

    10 import (

    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.

    18 func 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.

    49 func 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.

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

    60 	return shmget(key, size, flag)

    61 }