local: factor PreAllocate and SetSparse to lib/file

lib/file/preallocate_windows.go

@@ -0,0 +1,92 @@
+//+build windows
+
+package file
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+
+	"github.com/pkg/errors"
+	"golang.org/x/sys/windows"
+)
+
+var (
+	ntdll                        = windows.NewLazySystemDLL("ntdll.dll")
+	ntQueryVolumeInformationFile = ntdll.NewProc("NtQueryVolumeInformationFile")
+	ntSetInformationFile         = ntdll.NewProc("NtSetInformationFile")
+)
+
+type fileAllocationInformation struct {
+	AllocationSize uint64
+}
+
+type fileFsSizeInformation struct {
+	TotalAllocationUnits     uint64
+	AvailableAllocationUnits uint64
+	SectorsPerAllocationUnit uint32
+	BytesPerSector           uint32
+}
+
+type ioStatusBlock struct {
+	Status, Information uintptr
+}
+
+// PreAllocate the file for performance reasons
+func PreAllocate(size int64, out *os.File) error {
+	if size <= 0 {
+		return nil
+	}
+
+	var (
+		iosb       ioStatusBlock
+		fsSizeInfo fileFsSizeInformation
+		allocInfo  fileAllocationInformation
+	)
+
+	// Query info about the block sizes on the file system
+	_, _, e1 := ntQueryVolumeInformationFile.Call(
+		uintptr(out.Fd()),
+		uintptr(unsafe.Pointer(&iosb)),
+		uintptr(unsafe.Pointer(&fsSizeInfo)),
+		uintptr(unsafe.Sizeof(fsSizeInfo)),
+		uintptr(3), // FileFsSizeInformation
+	)
+	if e1 != nil && e1 != syscall.Errno(0) {
+		return errors.Wrap(e1, "preAllocate NtQueryVolumeInformationFile failed")
+	}
+
+	// Calculate the allocation size
+	clusterSize := uint64(fsSizeInfo.BytesPerSector) * uint64(fsSizeInfo.SectorsPerAllocationUnit)
+	if clusterSize <= 0 {
+		return errors.Errorf("preAllocate clusterSize %d <= 0", clusterSize)
+	}
+	allocInfo.AllocationSize = (1 + uint64(size-1)/clusterSize) * clusterSize
+
+	// Ask for the allocation
+	_, _, e1 = ntSetInformationFile.Call(
+		uintptr(out.Fd()),
+		uintptr(unsafe.Pointer(&iosb)),
+		uintptr(unsafe.Pointer(&allocInfo)),
+		uintptr(unsafe.Sizeof(allocInfo)),
+		uintptr(19), // FileAllocationInformation
+	)
+	if e1 != nil && e1 != syscall.Errno(0) {
+		return errors.Wrap(e1, "preAllocate NtSetInformationFile failed")
+	}
+
+	return nil
+}
+
+const (
+	FSCTL_SET_SPARSE = 0x000900c4
+)
+
+// SetSparse makes the file be a sparse file
+func SetSparse(out *os.File) error {
+	err := syscall.DeviceIoControl(syscall.Handle(out.Fd()), FSCTL_SET_SPARSE, nil, 0, nil, 0, nil, nil)
+	if err != nil {
+		return errors.Wrap(err, "DeviceIoControl FSCTL_SET_SPARSE")
+	}
+	return nil
+}