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1 // Copyright 2021 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 //go:build (darwin && !ios) || linux
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6 // +build darwin,!ios linux
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7
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8 package unix
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9
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10 import (
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11 "unsafe"
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12
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13 "golang.org/x/sys/internal/unsafeheader"
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14 )
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15
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16 // SysvShmAttach attaches the Sysv shared memory segment associated with the
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17 // shared memory identifier id.
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18 func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
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19 addr, errno := shmat(id, addr, flag)
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20 if errno != nil {
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21 return nil, errno
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22 }
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23
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24 // Retrieve the size of the shared memory to enable slice creation
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25 var info SysvShmDesc
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26
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27 _, err := SysvShmCtl(id, IPC_STAT, &info)
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28 if err != nil {
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29 // release the shared memory if we can't find the size
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30
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31 // ignoring error from shmdt as there's nothing sensible to return here
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32 shmdt(addr)
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33 return nil, err
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34 }
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35
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36 // Use unsafe to convert addr into a []byte.
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37 // TODO: convert to unsafe.Slice once we can assume Go 1.17
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38 var b []byte
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39 hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))
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40 hdr.Data = unsafe.Pointer(addr)
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41 hdr.Cap = int(info.Segsz)
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42 hdr.Len = int(info.Segsz)
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43 return b, nil
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44 }
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45
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46 // SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
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47 //
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48 // It is not safe to use the slice after calling this function.
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49 func SysvShmDetach(data []byte) error {
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50 if len(data) == 0 {
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51 return EINVAL
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52 }
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53
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54 return shmdt(uintptr(unsafe.Pointer(&data[0])))
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55 }
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56
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57 // SysvShmGet returns the Sysv shared memory identifier associated with key.
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58 // If the IPC_CREAT flag is specified a new segment is created.
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59 func SysvShmGet(key, size, flag int) (id int, err error) {
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60 return shmget(key, size, flag)
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61 }
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