1package drm
2
3import (
4 "errors"
5 "math"
6 "os"
7 "slices"
8 "time"
9 "unsafe"
10
11 "github.com/bnema/neferwl/internal/ports"
12 "golang.org/x/sys/unix"
13)
14
15// Direct scanout (ADR 006): when one fullscreen window covers the output
16// with a GPU buffer whose source can fill the plane, the output flips to that buffer
17// instead of compositing it. The buffer becomes a KMS framebuffer once
18// (PRIME import + ADDFB2) and is cached by DMABuf ID while the client
19// keeps using it. KMS waits on the buffer's implicit fences before showing
20// it. Anything else on screen or a buffer KMS refuses falls back to composition.
21
22const (
23 ioctlGemClose = 0x40086409
24 ioctlPrimeFDToHandle = 0xC00C642E
25 ioctlAddFB2 = 0xC06864B8
26
27 fbModifiers = 1 << 1
28 capAddFB2Modifiers = 0x10
29 modInvalid = 0x00ffffffffffffff
30 scanoutIdleTTL = 5 * time.Second // a cached framebuffer survives unused
31)
32
33type primeHandle struct {
34 handle, flags uint32
35 fd int32
36}
37
38type gemClose struct{ handle, pad uint32 }
39
40type fbCmd2 struct {
41 fbID, width, height, format, flags uint32
42 handles, pitches, offsets [4]uint32
43 modifiers [4]uint64
44}
45
46// planeRect contains source coordinates in 16.16 and destination pixels.
47type planeRect struct {
48 src [4]uint64
49 crtc [4]uint64
50}
51
52func fullPlaneRect(w, h int) planeRect {
53 return planeRect{src: [4]uint64{0, 0, uint64(w) << 16, uint64(h) << 16}, crtc: [4]uint64{0, 0, uint64(w), uint64(h)}}
54}
55
56func scanoutRect(c ports.SurfaceContent, w, h int) planeRect {
57 r := fullPlaneRect(w, h)
58 r.src = [4]uint64{0, 0, uint64(c.Width) << 16, uint64(c.Height) << 16}
59 if c.Source[2] != 0 {
60 for i, value := range c.Source {
61 r.src[i] = uint64(float64(value) * 65536)
62 }
63 }
64 return r
65}
66
67// covers reports whether win fills the output of scene s.
68func covers(s *ports.Scene, win *ports.SceneWindow) bool {
69 return (s.WorkspaceClip == (ports.Rect{}) || s.WorkspaceClip == (ports.Rect{W: s.OutputWidth, H: s.OutputHeight})) &&
70 win.Rect.X == 0 && win.Rect.Y == 0 && win.Rect.W == s.OutputWidth && win.Rect.H == s.OutputHeight
71}
72
73// fullscreenShown reports whether a visible fullscreen window covers the
74// output, whether its frame is scanned out or composed.
75func fullscreenShown(s *ports.Scene) bool {
76 for i := range s.Windows {
77 win := &s.Windows[i]
78 if win.Fullscreen && !win.Hidden && covers(s, win) {
79 return true
80 }
81 }
82 return false
83}
84
85// scanoutCandidate returns the window content the output can scan out
86// directly, or a reason why it cannot. w, h are the output's physical size.
87// The plane's formats are checked by scanoutFB.
88//
89// kept reports a window drawn from a content its client withdrew (it
90// closed and fades out): the client may already have its buffer back, so
91// it is never put on a plane (nil: none is).
92func scanoutCandidate(s ports.Scene, surfaces map[ports.WindowID]ports.SurfaceContent, w, h int, kept func(ports.WindowID) bool) (ports.SurfaceContent, string) {
93 if s.Transform != 0 {
94 // The scanout buffer would have to be pre-rotated: rotated outputs compose.
95 return ports.SurfaceContent{}, "output_transform"
96 }
97 if s.WorkspaceClip != (ports.Rect{}) && s.WorkspaceClip != (ports.Rect{W: s.OutputWidth, H: s.OutputHeight}) {
98 return ports.SurfaceContent{}, "workspace_clip"
99 }
100 var full *ports.SceneWindow
101 for i := range s.Windows {
102 win := &s.Windows[i]
103 if !s.Draws(*win) {
104 continue
105 }
106 if !win.Fullscreen || !covers(&s, win) || full != nil {
107 return ports.SurfaceContent{}, "other_windows"
108 }
109 full = win
110 }
111 if full == nil {
112 return ports.SurfaceContent{}, "no_fullscreen"
113 }
114 if kept != nil && kept(full.ID) {
115 return ports.SurfaceContent{}, "leaving"
116 }
117 if len(s.DropHints) > 0 {
118 // Drag hints are drawn over the window.
119 return ports.SurfaceContent{}, "drop_hint"
120 }
121 if full.Dim > 0 {
122 // Its veil is composed over it: the plane would show it bright.
123 return ports.SurfaceContent{}, "dim"
124 }
125 if full.Fade > 0 || full.Preview > 0 || full.Zoom > 0 {
126 // A fading or zoomed window is composed: the plane would show it
127 // whole and opaque.
128 return ports.SurfaceContent{}, "window_fade"
129 }
130 // Core leaves the layers a fullscreen window hides out of the scene:
131 // one above the windows here is drawn.
132 for _, l := range s.Layers {
133 if l.Layer >= ports.LayerTop && l.Rect.W > 0 && l.Rect.H > 0 {
134 return ports.SurfaceContent{}, "overlay_surface"
135 }
136 }
137 c := surfaces[full.ID]
138 if c.DMABuf == nil && len(c.Children) > 0 {
139 var reason string
140 if c, reason = clientSubsurface(c); reason != "" {
141 return c, reason
142 }
143 }
144 switch {
145 case c.DMABuf == nil:
146 return c, "not_dmabuf"
147 case c.Fade > 0:
148 // The plane would show it unfaded (wp_alpha_modifier_v1).
149 return c, "fade"
150 case len(c.Children) > 0:
151 return c, "subsurfaces"
152 case c.Transform != 0:
153 // Planes show buffers as they are: rotation is composed.
154 return c, "buffer_transform"
155 case c.LogicalW != full.Rect.W || c.LogicalH != full.Rect.H:
156 return c, "letterbox"
157 case c.Width <= 0 || c.Height <= 0 || c.Source[2] < 0 || c.Source[3] < 0 || !finiteSource(c.Source):
158 return c, "source_crop"
159 case c.Geometry != (ports.Rect{}) && (c.Geometry.X != 0 || c.Geometry.Y != 0 || c.Geometry.W != c.LogicalW || c.Geometry.H != c.LogicalH):
160 return c, "geometry_crop"
161 }
162 if c.Source[2] != 0 && (c.Source[0] < 0 || c.Source[1] < 0 || c.Source[2] <= 0 || c.Source[3] <= 0 || c.Source[0]+c.Source[2] > float32(c.Width) || c.Source[1]+c.Source[3] > float32(c.Height)) {
163 return c, "source_crop"
164 }
165 return c, ""
166}
167
168func finiteSource(src [4]float32) bool {
169 for _, n := range src {
170 if math.IsNaN(float64(n)) || math.IsInf(float64(n), 0) {
171 return false
172 }
173 }
174 return true
175}
176
177// cropped reports whether a viewport source shows less than the buffer.
178func cropped(c ports.SurfaceContent) bool {
179 return c.Source[2] != 0 && c.Source != [4]float32{0, 0, float32(c.Width), float32(c.Height)}
180}
181
182// clientSubsurface returns the content to scan out for a window whose
183// root has no GPU buffer but one opaque subsurface over its geometry: Wine
184// draws the frame in the root (wl_shm) and presents Vulkan in a subsurface
185// on the client area. That subsurface hides the root entirely, so it is
186// what the screen shows. The returned content keeps the window's ID and
187// Seq for release and presentation.
188func clientSubsurface(c ports.SurfaceContent) (ports.SurfaceContent, string) {
189 if len(c.Children) != 1 {
190 return c, "subsurfaces"
191 }
192 ch := c.Children[0]
193 switch {
194 case ch.DMABuf == nil:
195 return c, "not_dmabuf"
196 case !ch.Opaque:
197 return c, "subsurface_translucent"
198 case ch.Below:
199 // The root is drawn over it.
200 return c, "subsurface_below"
201 case ch.X != c.Geometry.X || ch.Y != c.Geometry.Y:
202 return c, "subsurface_offset"
203 }
204 out := ch.SurfaceContent
205 out.ID, out.Seq, out.Geometry = c.ID, c.Seq, ports.Rect{}
206 return out, ""
207}
208
209// scanoutFrame picks a fullscreen client buffer to flip directly. It
210// returns fb 0, with the reason logged on change, when the frame must be
211// composed.
212func (o *Output) scanoutFrame(scene ports.Scene, surfaces map[ports.WindowID]ports.SurfaceContent) (fb uint32, c ports.SurfaceContent, mode colorMode) {
213 reason := "disabled"
214 if o.scanout {
215 c, reason = scanoutCandidate(scene, surfaces, o.Width(), o.Height(), o.kept)
216 if reason == "" {
217 mode, reason = planeColor(c.Color, c.DMABuf.Format, c.Opaque, o.hdr.on, o.primary.pipeline)
218 }
219 }
220 if reason == "" {
221 fb, reason = o.scanoutFB(c.DMABuf, time.Now())
222 if reason == "" {
223 rect := scanoutRect(c, o.Width(), o.Height())
224 cfb := o.clientFBs[c.DMABuf.ID]
225 if cfb.scaleRefused && cfb.scaleFailed == rect {
226 reason = "scale_refused"
227 } else if rect != fullPlaneRect(o.Width(), o.Height()) && (!cfb.scaleTestedOK || cfb.scaleTested != rect) {
228 req := &o.probeReq
229 req.reset()
230 o.primaryRectProps(req, fb, rect)
231 if err := o.k.commit(req, atomicTestOnly, 0); err != nil {
232 cfb.scaleFailed = rect
233 cfb.scaleRefused = true
234 reason = "scale_refused"
235 o.renderLog.Info().Err(err).Str("reason", reason).Str("connector", o.conn.name).Msg("scanout scaling refused")
236 } else {
237 cfb.scaleTested = rect
238 cfb.scaleTestedOK = true
239 }
240 }
241 if reason == "" && mode != colorBypass && !o.colorAllowed(o.primary, c.DMABuf.Format, func(req *atomicReq) {
242 o.primaryRectProps(req, fb, rect)
243 if o.overlayOn != 0 {
244 o.overlayProps(req, overlayWin{})
245 }
246 }) {
247 reason = "color_refused"
248 }
249 }
250 }
251 o.setScanoutReason(reason)
252 if reason != "" {
253 return 0, c, colorBypass
254 }
255 return fb, c, mode
256}
257
258// overlayFrame decides the overlay of a frame: the window, and the scene
259// the renderer composes (the window left out). A zero overlayWin means
260// none; the reason is logged on change. The returned scene's Windows is
261// valid until the next call: it reuses o.restWindows (its consumers, Render,
262// ExcludedScene and the capture tracking, run synchronously before then).
263func (o *Output) overlayFrame(s ports.Scene, surfaces map[ports.WindowID]ports.SurfaceContent) (overlayWin, ports.Scene) {
264 reason := "no_plane"
265 var ov overlayWin
266 if o.overlay != nil && o.scanout {
267 var w ports.SceneWindow
268 var c ports.SurfaceContent
269 var mode colorMode
270 w, c, mode, reason = overlayCandidate(s, surfaces, o.hdr.on, o.overlay.pipeline, o.kept)
271 if reason == "" && mode != colorBypass {
272 if ok, known := o.overlay.verdict(c.DMABuf.Format, o.cursorShown()); known && !ok {
273 reason = "color_refused"
274 }
275 }
276 if reason == "" {
277 var fb uint32
278 if fb, reason = o.overlayFB(c.DMABuf, time.Now()); reason == "" {
279 scale := s.Scale
280 if scale <= 0 {
281 scale = 1
282 }
283 ov = overlayWin{id: w.ID, fb: fb, buf: c.DMABuf.ID, w: c.Width, h: c.Height,
284 rect: ports.Rect{X: int(float64(w.Rect.X) * scale), Y: int(float64(w.Rect.Y) * scale), W: c.Width, H: c.Height},
285 acquire: dupFence(c.Acquire), color: colorUse{mode: mode, format: c.DMABuf.Format}}
286 }
287 }
288 }
289 o.setOverlayReason(reason)
290 if ov.id == 0 {
291 return overlayWin{}, s
292 }
293 // The composed frame leaves the window out: the overlay shows it.
294 rest := s
295 o.restWindows = o.restWindows[:0]
296 for _, w := range s.Windows {
297 if w.ID != ov.id {
298 o.restWindows = append(o.restWindows, w)
299 }
300 }
301 rest.Windows = o.restWindows
302 return ov, rest
303}
304
305// frameDecision selects the zero-copy path or the scene to compose.
306type frameDecision struct {
307 fb uint32
308 content ports.SurfaceContent
309 rect planeRect
310 color colorMode // how the primary plane shows fb
311 overlay overlayWin
312 composed ports.Scene
313}
314
315// composeFrame chooses overlay or composition after direct scanout cannot commit.
316// The caller owns the returned overlay fence.
317func (o *Output) composeFrame(s ports.Scene, surfaces map[ports.WindowID]ports.SurfaceContent) frameDecision {
318 ov, rest := o.overlayFrame(s, surfaces)
319 if ov.fb != 0 {
320 return frameDecision{overlay: ov, composed: rest}
321 }
322 return frameDecision{composed: s}
323}
324
325// decideFrame tries direct scanout, then overlay, then composition.
326// Captures require composition; the caller owns the returned overlay fence.
327func (o *Output) decideFrame(s ports.Scene, surfaces map[ports.WindowID]ports.SurfaceContent, capture bool) frameDecision {
328 if capture {
329 o.setScanoutReason("capture")
330 o.setOverlayReason("capture")
331 return frameDecision{composed: s}
332 }
333 fb, c, mode := o.scanoutFrame(s, surfaces)
334 if fb != 0 {
335 return frameDecision{fb: fb, content: c, rect: scanoutRect(c, o.Width(), o.Height()), color: mode}
336 }
337 return o.composeFrame(s, surfaces)
338}
339
340// setScanoutReason logs a direct-scanout transition once.
341func (o *Output) setScanoutReason(reason string) {
342 if reason != o.reason {
343 o.renderLog.Info().Bool("direct_scanout", reason == "").Str("reason", reason).Str("connector", o.conn.name).Msg("scanout")
344 o.reason = reason
345 }
346}
347
348// setOverlayReason logs an overlay transition once.
349func (o *Output) setOverlayReason(reason string) {
350 if reason != o.overlayReason {
351 o.renderLog.Info().Bool("overlay", reason == "").Str("reason", reason).Str("connector", o.conn.name).Msg("overlay")
352 o.overlayReason = reason
353 }
354}
355
356// clientFB is a client buffer imported as a KMS framebuffer.
357type clientFB struct {
358 fbID uint32
359 last time.Time // when last wanted on screen
360 // failed is the reason KMS refused the buffer; it is not retried.
361 failed string
362 // noAsync: KMS refused an async flip to it; it flips at vblank.
363 noAsync bool
364 scaleTested, scaleFailed planeRect
365 scaleRefused, scaleTestedOK bool
366 // overlayFailed is why the overlay plane refused it; kept apart from
367 // failed, so a refusal on one plane does not bar the other.
368 overlayFailed string
369 importErr bool
370}
371
372// scanoutFB returns the framebuffer of a client buffer for the primary
373// plane, importing it on first use. A buffer KMS refuses is remembered
374// with its reason.
375func (o *Output) scanoutFB(b *ports.DMABuf, now time.Time) (uint32, string) {
376 return o.planeFB(o.primary, b, now, func(fb *clientFB) *string { return &fb.failed })
377}
378
379// overlayFB is scanoutFB for the overlay plane, with its own formats and
380// refusal reason.
381func (o *Output) overlayFB(b *ports.DMABuf, now time.Time) (uint32, string) {
382 return o.planeFB(o.overlay, b, now, func(fb *clientFB) *string { return &fb.overlayFailed })
383}
384
385// planeFB imports b once as a framebuffer; reason is the plane's refusal
386// field. Both planes share the framebuffer: they show the same format.
387func (o *Output) planeFB(p *plane, b *ports.DMABuf, now time.Time, reason func(*clientFB) *string) (uint32, string) {
388 fb := o.clientFBs[b.ID]
389 if fb == nil {
390 fb = &clientFB{}
391 o.clientFBs[b.ID] = fb
392 }
393 fb.last = now
394 why := reason(fb)
395 if *why != "" {
396 return 0, *why
397 }
398 format, ok := planeFormat(p, b)
399 if !ok {
400 *why = "format"
401 return 0, *why
402 }
403 if fb.fbID == 0 {
404 if fb.importErr {
405 *why = "import_failed"
406 return 0, *why
407 }
408 id, err := o.k.addFB(b, format)
409 if err != nil {
410 o.renderLog.Info().Err(err).Uint32("format", b.Format).Uint64("modifier", b.Modifier).Msg("scanout import failed")
411 fb.importErr, *why = true, "import_failed"
412 return 0, *why
413 }
414 fb.fbID = id
415 }
416 return fb.fbID, ""
417}
418
419// scanoutFormat is the framebuffer format a client buffer is scanned out
420// as on the primary plane (see planeFormat).
421func (o *Output) scanoutFormat(b *ports.DMABuf) (uint32, bool) { return planeFormat(o.primary, b) }
422
423// planeFormat is the framebuffer format a client buffer shows as on p,
424// when p lists it with the buffer's modifier. Planes here show no alpha:
425// an alpha format goes as its X variant when the plane has that one.
426func planeFormat(p *plane, b *ports.DMABuf) (uint32, bool) {
427 has := func(f uint32) bool {
428 return slices.Contains(p.formats, ports.DMABufFormat{Format: f, Modifier: b.Modifier})
429 }
430 if x, ok := opaqueVariant[b.Format]; ok && has(x) {
431 return x, true
432 }
433 return b.Format, has(b.Format)
434}
435
436// opaqueVariant maps alpha formats to the same layout without alpha.
437var opaqueVariant = map[uint32]uint32{
438 fourccARGB: fourccXRGB,
439 fourccABGR: fourccXBGR,
440 fourccAR30: fourccXR30,
441 fourccAB30: fourccXB30,
442 fourccAR4H: fourccXR4H,
443 fourccAB4H: fourccXB4H,
444}
445
446// scanoutFormats are the formats a buffer can be scanned out with: in the
447// primary plane's IN_FORMATS (directly or as its opaque variant) and
448// composable by the renderer.
449func (o *Output) scanoutFormats(sampled []ports.DMABufFormat) []ports.DMABufFormat {
450 var out []ports.DMABufFormat
451 for _, f := range sampled {
452 b := ports.DMABuf{Format: f.Format, Modifier: f.Modifier}
453 if _, ok := o.scanoutFormat(&b); ok {
454 out = append(out, f)
455 }
456 }
457 return out
458}
459
460// isYUVFormat identifies video formats which are always composed, never scanned out.
461func isYUVFormat(format uint32) bool {
462 return format == fourccNV12 || format == fourccP010
463}
464
465// isTenBit identifies the packed 2101010 formats supported by the renderer.
466func isTenBit(format uint32) bool {
467 switch format {
468 case fourccXR30, fourccAR30, fourccXB30, fourccAB30:
469 return true
470 }
471 return false
472}
473
474const (
475 fourccNV12 = 'N' | 'V'<<8 | '1'<<16 | '2'<<24
476 fourccP010 = 'P' | '0'<<8 | '1'<<16 | '0'<<24
477 fourccXRGB = 'X' | 'R'<<8 | '2'<<16 | '4'<<24
478 fourccARGB = 'A' | 'R'<<8 | '2'<<16 | '4'<<24
479 fourccXBGR = 'X' | 'B'<<8 | '2'<<16 | '4'<<24
480 fourccABGR = 'A' | 'B'<<8 | '2'<<16 | '4'<<24
481 fourccXR30 = 'X' | 'R'<<8 | '3'<<16 | '0'<<24
482 fourccAR30 = 'A' | 'R'<<8 | '3'<<16 | '0'<<24
483 fourccXB30 = 'X' | 'B'<<8 | '3'<<16 | '0'<<24
484 fourccAB30 = 'A' | 'B'<<8 | '3'<<16 | '0'<<24
485 fourccXR4H = 'X' | 'R'<<8 | '4'<<16 | 'H'<<24
486 fourccAR4H = 'A' | 'R'<<8 | '4'<<16 | 'H'<<24
487 fourccXB4H = 'X' | 'B'<<8 | '4'<<16 | 'H'<<24
488 fourccAB4H = 'A' | 'B'<<8 | '4'<<16 | 'H'<<24
489)
490
491// addFB imports a dmabuf as a framebuffer of the given fourcc: client buffers, the renderer's
492// output images and cursor images. The GEM handle belongs to the card fd
493// and is shared by every import of the same buffer, so import, ADDFB2 and
494// close run under the lock and the handle is closed right away: the
495// framebuffer keeps its own reference to the buffer.
496func (k kmsDevice) addFB(b *ports.DMABuf, format uint32) (uint32, error) {
497 raw, err := b.Planes[0].File.SyscallConn()
498 if err != nil {
499 return 0, err
500 }
501 k.gemMu.Lock()
502 defer k.gemMu.Unlock()
503 var p primeHandle
504 var ioErr error
505 if err := raw.Control(func(fd uintptr) {
506 p.fd = int32(fd)
507 ioErr = ioctl(k.fd, ioctlPrimeFDToHandle, unsafe.Pointer(&p))
508 }); err != nil {
509 return 0, err
510 }
511 if ioErr != nil {
512 return 0, errors.Join(errors.New("prime import"), ioErr)
513 }
514 defer func() {
515 g := gemClose{handle: p.handle}
516 _ = ioctl(k.fd, ioctlGemClose, unsafe.Pointer(&g))
517 }()
518 cmd := fbCmd2{width: uint32(b.Width), height: uint32(b.Height), format: format}
519 useMod := b.Modifier != modInvalid && (b.Modifier != 0 || k.modifiers)
520 if useMod {
521 cmd.flags = fbModifiers
522 }
523 // Planes in the same dmabuf share its GEM handle: each distinct
524 // handle is closed once.
525 closing := map[uint32]bool{p.handle: true}
526 for i, pl := range b.Planes {
527 if i >= len(cmd.handles) {
528 break
529 }
530 h := p.handle
531 if i > 0 {
532 var err error
533 if h, err = k.primeImport(pl.File); err != nil {
534 return 0, err
535 }
536 if !closing[h] {
537 closing[h] = true
538 defer k.gemClose(h)
539 }
540 }
541 cmd.handles[i], cmd.pitches[i], cmd.offsets[i] = h, pl.Stride, pl.Offset
542 if useMod {
543 cmd.modifiers[i] = b.Modifier
544 }
545 }
546 if err := ioctl(k.fd, ioctlAddFB2, unsafe.Pointer(&cmd)); err != nil {
547 return 0, errors.Join(errors.New("add fb2"), err)
548 }
549 return cmd.fbID, nil
550}
551
552// primeImport returns the GEM handle of a dmabuf file. The caller holds
553// gemMu and closes the handle.
554func (k kmsDevice) primeImport(f *os.File) (uint32, error) {
555 raw, err := f.SyscallConn()
556 if err != nil {
557 return 0, err
558 }
559 var p primeHandle
560 var ioErr error
561 if err := raw.Control(func(fd uintptr) {
562 p.fd = int32(fd)
563 ioErr = ioctl(k.fd, ioctlPrimeFDToHandle, unsafe.Pointer(&p))
564 }); err != nil {
565 return 0, err
566 }
567 if ioErr != nil {
568 return 0, errors.Join(errors.New("prime import"), ioErr)
569 }
570 return p.handle, nil
571}
572
573func (k kmsDevice) gemClose(h uint32) {
574 g := gemClose{handle: h}
575 _ = ioctl(k.fd, ioctlGemClose, unsafe.Pointer(&g))
576}
577
578// dropClientFBs frees framebuffers not wanted for scanoutIdleTTL, or all
579// of them, except those on screen or queued.
580func (o *Output) dropClientFBs(now time.Time, all bool) {
581 for id, fb := range o.clientFBs {
582 if id == o.shown || id == o.queued {
583 continue
584 }
585 if !all && now.Sub(fb.last) < scanoutIdleTTL {
586 continue
587 }
588 if fb.fbID != 0 {
589 _ = o.k.rmFB(fb.fbID)
590 // KMS may give the id to another buffer.
591 o.forgetOverlayProbes()
592 }
593 delete(o.clientFBs, id)
594 }
595}
596
597// dupFence duplicates a sync file under its SyscallConn, so a concurrent
598// Close cannot hand us a reused fd; nil when f is nil or closed.
599func dupFence(f *os.File) *os.File {
600 if f == nil {
601 return nil
602 }
603 raw, err := f.SyscallConn()
604 if err != nil {
605 return nil
606 }
607 fd := -1
608 if raw.Control(func(v uintptr) { fd, _ = unix.FcntlInt(v, unix.F_DUPFD_CLOEXEC, 0) }) != nil || fd < 0 {
609 return nil
610 }
611 return os.NewFile(uintptr(fd), "acquire-fence")
612}