143 lines
4 KiB
Go
143 lines
4 KiB
Go
// Copyright 2011 Evan Shaw. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package mmap
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import (
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"errors"
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"os"
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"sync"
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"golang.org/x/sys/windows"
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)
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// mmap on Windows is a two-step process.
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// First, we call CreateFileMapping to get a handle.
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// Then, we call MapviewToFile to get an actual pointer into memory.
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// Because we want to emulate a POSIX-style mmap, we don't want to expose
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// the handle -- only the pointer. We also want to return only a byte slice,
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// not a struct, so it's convenient to manipulate.
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// We keep this map so that we can get back the original handle from the memory address.
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type addrinfo struct {
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file windows.Handle
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mapview windows.Handle
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}
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var handleLock sync.Mutex
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var handleMap = map[uintptr]*addrinfo{}
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func mmap(len int, prot, flags, hfile uintptr, off int64) ([]byte, error) {
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flProtect := uint32(windows.PAGE_READONLY)
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dwDesiredAccess := uint32(windows.FILE_MAP_READ)
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switch {
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case prot© != 0:
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flProtect = windows.PAGE_WRITECOPY
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dwDesiredAccess = windows.FILE_MAP_COPY
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case prot&RDWR != 0:
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flProtect = windows.PAGE_READWRITE
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dwDesiredAccess = windows.FILE_MAP_WRITE
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}
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if prot&EXEC != 0 {
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flProtect <<= 4
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dwDesiredAccess |= windows.FILE_MAP_EXECUTE
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}
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// The maximum size is the area of the file, starting from 0,
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// that we wish to allow to be mappable. It is the sum of
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// the length the user requested, plus the offset where that length
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// is starting from. This does not map the data into memory.
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maxSizeHigh := uint32((off + int64(len)) >> 32)
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maxSizeLow := uint32((off + int64(len)) & 0xFFFFFFFF)
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// TODO: Do we need to set some security attributes? It might help portability.
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h, errno := windows.CreateFileMapping(windows.Handle(hfile), nil, flProtect, maxSizeHigh, maxSizeLow, nil)
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if h == 0 {
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return nil, os.NewSyscallError("CreateFileMapping", errno)
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}
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// Actually map a view of the data into memory. The view's size
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// is the length the user requested.
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fileOffsetHigh := uint32(off >> 32)
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fileOffsetLow := uint32(off & 0xFFFFFFFF)
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addr, errno := windows.MapViewOfFile(h, dwDesiredAccess, fileOffsetHigh, fileOffsetLow, uintptr(len))
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if addr == 0 {
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return nil, os.NewSyscallError("MapViewOfFile", errno)
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}
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handleLock.Lock()
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handleMap[addr] = &addrinfo{
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file: windows.Handle(hfile),
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mapview: h,
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}
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handleLock.Unlock()
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m := MMap{}
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dh := m.header()
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dh.Data = addr
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dh.Len = len
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dh.Cap = dh.Len
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return m, nil
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}
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func (m MMap) flush() error {
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addr, len := m.addrLen()
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errno := windows.FlushViewOfFile(addr, len)
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if errno != nil {
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return os.NewSyscallError("FlushViewOfFile", errno)
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}
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handleLock.Lock()
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defer handleLock.Unlock()
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handle, ok := handleMap[addr]
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if !ok {
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// should be impossible; we would've errored above
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return errors.New("unknown base address")
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}
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errno = windows.FlushFileBuffers(handle.file)
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return os.NewSyscallError("FlushFileBuffers", errno)
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}
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func (m MMap) lock() error {
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addr, len := m.addrLen()
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errno := windows.VirtualLock(addr, len)
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return os.NewSyscallError("VirtualLock", errno)
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}
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func (m MMap) unlock() error {
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addr, len := m.addrLen()
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errno := windows.VirtualUnlock(addr, len)
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return os.NewSyscallError("VirtualUnlock", errno)
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}
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func (m MMap) unmap() error {
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err := m.flush()
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if err != nil {
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return err
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}
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addr := m.header().Data
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// Lock the UnmapViewOfFile along with the handleMap deletion.
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// As soon as we unmap the view, the OS is free to give the
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// same addr to another new map. We don't want another goroutine
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// to insert and remove the same addr into handleMap while
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// we're trying to remove our old addr/handle pair.
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handleLock.Lock()
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defer handleLock.Unlock()
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err = windows.UnmapViewOfFile(addr)
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if err != nil {
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return err
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}
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handle, ok := handleMap[addr]
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if !ok {
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// should be impossible; we would've errored above
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return errors.New("unknown base address")
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}
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delete(handleMap, addr)
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e := windows.CloseHandle(windows.Handle(handle.mapview))
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return os.NewSyscallError("CloseHandle", e)
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}
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