refactor(reflinking): add windows ReFS filesystem support (#1576)

Co-authored-by: soup <s0up4200@pm.me>

Author: Audionut

documentation/docs/features/cross-seed/hardlink-mode.md

@@ -88,7 +88,7 @@ Reflink mode creates copy-on-write clones of the matched files. Unlike hardlinks
 ### When to Use Reflink Mode
 
 - You want to cross-seed torrents that hardlink mode would skip due to "extra files share pieces with content"
-- Your filesystem supports copy-on-write clones (BTRFS, XFS on Linux; APFS on macOS)
+- Your filesystem supports copy-on-write clones (BTRFS, XFS on Linux; APFS on macOS; ReFS on Windows)
 - You prefer the safety of copy-on-write over hardlinks
 
 ### Reflink Requirements
@@ -99,7 +99,12 @@ Reflink mode creates copy-on-write clones of the matched files. Unlike hardlinks
 - The filesystem must support reflinks:
   - **Linux**: BTRFS, XFS (with reflink=1), and similar CoW filesystems
   - **macOS**: APFS
-  - **Windows/FreeBSD**: Not currently supported
+  - **Windows**: ReFS on the same volume as the source files and reflink base directory
+  - **FreeBSD**: Not currently supported
+
+:::note
+Windows reflink mode uses ReFS block cloning (requiring a ReFS filesystem). NTFS is not supported. If the matched source path is a symlink, qui resolves it before cloning, and the resolved source plus the reflink base directory still need to be on the same ReFS volume. If reflink creation fails, fallback still depends on the existing "Fallback to regular mode" setting.
+:::
 
 :::tip
 On Linux, check the filesystem type with `df -T /path` (you want `xfs`/`btrfs`, not `fuseblk`/`fuse.mergerfs`/`overlayfs`).

internal/services/crossseed/hardlink_mode_test.go

@@ -5,6 +5,8 @@ package crossseed
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -16,6 +18,7 @@ import (
 
 	"github.com/autobrr/qui/internal/models"
 	"github.com/autobrr/qui/pkg/hardlinktree"
+	"github.com/autobrr/qui/pkg/reflinktree"
 )
 
 // Note: qbtLayoutToHardlinkLayout is no longer used in hardlink mode.
@@ -904,3 +907,39 @@ func TestProcessReflinkMode_FallbackDisabled(t *testing.T) {
 	assert.Equal(t, "reflink_error", result.Result.Status)
 	assert.Contains(t, result.Result.Message, "base directory")
 }
+
+func TestShouldWarnForReflinkCreateError(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{
+			name: "plain wrapped unsupported error",
+			err:  fmt.Errorf("reflink create failed: %w", reflinktree.ErrReflinkUnsupported),
+			want: true,
+		},
+		{
+			name: "joined rollback error stays error level",
+			err: errors.Join(
+				fmt.Errorf("reflink create failed: %w", reflinktree.ErrReflinkUnsupported),
+				errors.New("rollback also failed"),
+			),
+			want: false,
+		},
+		{
+			name: "unrelated error",
+			err:  errors.New("boom"),
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			assert.Equal(t, tt.want, shouldWarnForReflinkCreateError(tt.err))
+		})
+	}
+}

internal/services/crossseed/service.go

@@ -10861,6 +10861,19 @@ type reflinkModeResult struct {
 	Result InstanceCrossSeedResult
 }
 
+func shouldWarnForReflinkCreateError(err error) bool {
+	if !errors.Is(err, reflinktree.ErrReflinkUnsupported) {
+		return false
+	}
+
+	type multiUnwrapper interface {
+		Unwrap() []error
+	}
+
+	var joined multiUnwrapper
+	return !errors.As(err, &joined)
+}
+
 // processReflinkMode attempts to add a cross-seed torrent using reflink (copy-on-write) mode.
 // This creates a reflink tree matching the incoming torrent's layout, allowing safe
 // modification of cloned files without affecting originals.
@@ -11081,7 +11094,11 @@ func (s *Service) processReflinkMode(
 
 	// Create reflink tree on disk
 	if err := reflinktree.Create(plan); err != nil {
-		log.Error().
+		logEvent := log.Error()
+		if shouldWarnForReflinkCreateError(err) {
+			logEvent = log.Warn()
+		}
+		logEvent.
 			Err(err).
 			Int("instanceID", candidate.InstanceID).
 			Str("torrentName", torrentName).

pkg/reflinktree/reflink_test.go

@@ -17,8 +17,8 @@ func TestSupportsReflink(t *testing.T) {
 
 	supported, reason := SupportsReflink(tmpDir)
 
-	// On unsupported platforms, should return false
-	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+	// On unsupported platforms, should return false.
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" && runtime.GOOS != "windows" {
 		if supported {
 			t.Errorf("SupportsReflink should return false on %s", runtime.GOOS)
 		}
@@ -28,8 +28,8 @@ func TestSupportsReflink(t *testing.T) {
 		return
 	}
 
-	// On supported platforms, the result depends on filesystem
-	// We just verify the function doesn't panic and returns sensible values
+	// On supported platforms, the result depends on filesystem.
+	// We just verify the function doesn't panic and returns sensible values.
 	t.Logf("SupportsReflink(%s): supported=%v, reason=%s", tmpDir, supported, reason)
 
 	if !supported {

pkg/reflinktree/reflink_unsupported.go

@@ -1,12 +1,12 @@
 // Copyright (c) 2025-2026, s0up and the autobrr contributors.
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-//go:build !linux && !darwin
+//go:build !linux && !darwin && !windows
 
 package reflinktree
 
 // SupportsReflink returns false on unsupported platforms.
-// Windows and FreeBSD do not have a standard reflink mechanism that we support.
+// FreeBSD do not have a standard reflink mechanism that we support.
 func SupportsReflink(_ string) (supported bool, reason string) {
 	return false, "reflink is not supported on this operating system"
 }