syncthing/lib/fs/basicfs_copy_range_duplicateextents.go

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// Copyright (C) 2020 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
// +build windows
package fs
import (
"io"
"syscall"
"unsafe"
"golang.org/x/sys/windows"
)
func init() {
registerCopyRangeImplementation(CopyRangeMethodDuplicateExtents, copyRangeImplementationForBasicFile(copyRangeDuplicateExtents))
}
// Inspired by https://github.com/git-lfs/git-lfs/blob/master/tools/util_windows.go
var (
availableClusterSize = []int64{64 * 1024, 4 * 1024} // ReFS only supports 64KiB and 4KiB cluster.
GiB = int64(1024 * 1024 * 1024)
)
// fsctlDuplicateExtentsToFile = FSCTL_DUPLICATE_EXTENTS_TO_FILE IOCTL
// Instructs the file system to copy a range of file bytes on behalf of an application.
//
// https://docs.microsoft.com/windows/win32/api/winioctl/ni-winioctl-fsctl_duplicate_extents_to_file
const fsctlDuplicateExtentsToFile = 623428
// duplicateExtentsData = DUPLICATE_EXTENTS_DATA structure
// Contains parameters for the FSCTL_DUPLICATE_EXTENTS control code that performs the Block Cloning operation.
//
// https://docs.microsoft.com/windows/win32/api/winioctl/ns-winioctl-duplicate_extents_data
type duplicateExtentsData struct {
FileHandle windows.Handle
SourceFileOffset int64
TargetFileOffset int64
ByteCount int64
}
func copyRangeDuplicateExtents(src, dst basicFile, srcOffset, dstOffset, size int64) error {
var err error
// Check that the destination file has sufficient space
dstFi, err := dst.Stat()
if err != nil {
return err
}
dstSize := dstFi.Size()
if dstSize < dstOffset+size {
// set file size. There is a requirements "The destination region must not extend past the end of file."
if err = dst.Truncate(dstOffset + size); err != nil {
return err
}
dstSize = dstOffset + size
}
// The source file has to be big enough
if fi, err := src.Stat(); err != nil {
return err
} else if fi.Size() < srcOffset+size {
return io.ErrUnexpectedEOF
}
// Requirement
// * The source and destination regions must begin and end at a cluster boundary. (4KiB or 64KiB)
// * cloneRegionSize less than 4GiB.
// see https://docs.microsoft.com/windows/win32/fileio/block-cloning
smallestClusterSize := availableClusterSize[len(availableClusterSize)-1]
if srcOffset%smallestClusterSize != 0 || dstOffset%smallestClusterSize != 0 {
return syscall.EINVAL
}
// Each file gets allocated multiple of "clusterSize" blocks, yet file size determines how much of the last block
// is readable/visible.
// Copies only happen in block sized chunks, hence you can copy non block sized regions of data to a file, as long
// as the regions are copied at the end of the file where the block visibility is adjusted by the file size.
if size%smallestClusterSize != 0 && dstOffset+size != dstSize {
return syscall.EINVAL
}
// Clone first xGiB region.
for size > GiB {
_, err = withFileDescriptors(src, dst, func(srcFd, dstFd uintptr) (int, error) {
return 0, callDuplicateExtentsToFile(srcFd, dstFd, srcOffset, dstOffset, GiB)
})
if err != nil {
return wrapError(err)
}
size -= GiB
srcOffset += GiB
dstOffset += GiB
}
// Clone tail. First try with 64KiB round up, then fallback to 4KiB.
for _, cloneRegionSize := range availableClusterSize {
_, err = withFileDescriptors(src, dst, func(srcFd, dstFd uintptr) (int, error) {
return 0, callDuplicateExtentsToFile(srcFd, dstFd, srcOffset, dstOffset, roundUp(size, cloneRegionSize))
})
if err != nil {
continue
}
break
}
return wrapError(err)
}
func wrapError(err error) error {
if err == windows.SEVERITY_ERROR {
return syscall.ENOTSUP
}
return err
}
// call FSCTL_DUPLICATE_EXTENTS_TO_FILE IOCTL
// see https://docs.microsoft.com/en-us/windows/win32/api/winioctl/ni-winioctl-fsctl_duplicate_extents_to_file
//
// memo: Overflow (cloneRegionSize is greater than file ends) is safe and just ignored by windows.
func callDuplicateExtentsToFile(src, dst uintptr, srcOffset, dstOffset int64, cloneRegionSize int64) error {
var (
bytesReturned uint32
overlapped windows.Overlapped
)
request := duplicateExtentsData{
FileHandle: windows.Handle(src),
SourceFileOffset: srcOffset,
TargetFileOffset: dstOffset,
ByteCount: cloneRegionSize,
}
return windows.DeviceIoControl(
windows.Handle(dst),
fsctlDuplicateExtentsToFile,
(*byte)(unsafe.Pointer(&request)),
uint32(unsafe.Sizeof(request)),
(*byte)(unsafe.Pointer(nil)), // = nullptr
0,
&bytesReturned,
&overlapped)
}
func roundUp(value, base int64) int64 {
mod := value % base
if mod == 0 {
return value
}
return value - mod + base
}