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internal/poll: don't call Seek for overlapped Windows handles

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Overlapped handles don't have the file pointer updated when performing
I/O operations, so there is no need to call FD.Seek to reset the file
pointer.

Also, some overlapped file handles don't support seeking. See #74951.

Fixes #74951.

Change-Id: I0edd53beed7d3862730f3b2ed5fe9ba490e66c06
Reviewed-on: https://go-review.googlesource.com/c/go/+/697295
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
This commit is contained in:
qmuntal 2025-08-19 13:00:02 +02:00 • committed by Quim Muntal
parent 853fc12739
commit 509d5f647f
2 changed files with 58 additions and 10 deletions
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40
src/internal/poll/fd_windows.go
View file

@ -622,12 +622,22 @@ func (fd *FD) Pread(b []byte, off int64) (int, error) {
fd.l.Lock()
defer fd.l.Unlock()
curoffset, err := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
if err != nil {
return 0, err
if fd.isBlocking {
curoffset, err := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
if err != nil {
return 0, err
}
defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
defer fd.setOffset(curoffset)
} else {
// Overlapped handles don't have the file pointer updated
// when performing I/O operations, so there is no need to
// call Seek to reset the file pointer.
// Also, some overlapped file handles don't support seeking.
// See https://go.dev/issues/74951.
curoffset := fd.offset
defer fd.setOffset(curoffset)
}
defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
defer fd.setOffset(curoffset)
o := &fd.rop
o.InitBuf(b)
fd.setOffset(off)
@ -847,12 +857,22 @@ func (fd *FD) Pwrite(buf []byte, off int64) (int, error) {
fd.l.Lock()
defer fd.l.Unlock()
curoffset, err := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
if err != nil {
return 0, err
if fd.isBlocking {
curoffset, err := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
if err != nil {
return 0, err
}
defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
defer fd.setOffset(curoffset)
} else {
// Overlapped handles don't have the file pointer updated
// when performing I/O operations, so there is no need to
// call Seek to reset the file pointer.
// Also, some overlapped file handles don't support seeking.
// See https://go.dev/issues/74951.
curoffset := fd.offset
defer fd.setOffset(curoffset)
}
defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
defer fd.setOffset(curoffset)
var ntotal int
for {

28
src/os/os_windows_test.go
View file

@ -1883,6 +1883,34 @@ func TestFileOverlappedSeek(t *testing.T) {
}
}
func TestFileOverlappedReadAtVolume(t *testing.T) {
// Test that we can use File.ReadAt with an overlapped volume handle.
// See https://go.dev/issues/74951.
t.Parallel()
name := `\\.\` + filepath.VolumeName(t.TempDir())
namep, err := syscall.UTF16PtrFromString(name)
if err != nil {
t.Fatal(err)
}
h, err := syscall.CreateFile(namep,
syscall.GENERIC_READ|syscall.GENERIC_WRITE,
syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_READ,
nil, syscall.OPEN_ALWAYS, syscall.FILE_FLAG_OVERLAPPED, 0)
if err != nil {
if errors.Is(err, syscall.ERROR_ACCESS_DENIED) {
t.Skip("skipping test: access denied")
}
t.Fatal(err)
}
f := os.NewFile(uintptr(h), name)
defer f.Close()
var buf [0]byte
if _, err := f.ReadAt(buf[:], 0); err != nil {
t.Fatal(err)
}
}
func TestPipe(t *testing.T) {
t.Parallel()
r, w, err := os.Pipe()