Split the harness stream into capture, encode, and per-client send loops

harness/grab.go

@@ -36,6 +36,9 @@ func openGrabber() (*grabber, error) {
 		}
 		crtc, index, err := activeCrtc(fd)
 		if err == nil {
+			// Opening the node while no master exists hands this fd implicit
+			// drm master; give it back so cabletest can take it.
+			drm.Ioctl(fd, drm.DropMaster, nil)
 			return &grabber{fd: fd, crtc: crtc, index: index}, nil
 		}
 		unix.Close(fd)
@@ -129,7 +132,7 @@ const overrunLimit = 10
 // sequences differ by at most one therefore provably finished before the
 // rewrite could begin. Overrunning that is a timing miss, not corruption:
 // sample again, and treat only systematic misses as an error.
-func (g *grabber) rawFrame(dst []byte) ([]byte, int, int, int, error) {
+func (g *grabber) rawFrame() ([]byte, int, int, int, error) {
 	for tries := 0; tries < overrunLimit; tries++ {
 		s0, err := g.vblank(1)
 		if err != nil {
@@ -139,10 +142,7 @@ func (g *grabber) rawFrame(dst []byte) ([]byte, int, int, int, error) {
 		if err != nil {
 			return nil, 0, 0, 0, err
 		}
-		if len(dst) < len(mem) {
-			dst = make([]byte, len(mem))
-		}
-		dst = dst[:len(mem)]
+		dst := make([]byte, len(mem))
 		copy(dst, mem)
 		unix.Munmap(mem)
 		s1, err := g.vblank(0)
@@ -157,7 +157,7 @@ func (g *grabber) rawFrame(dst []byte) ([]byte, int, int, int, error) {
 }
 
 func (g *grabber) frame() (*image.NRGBA, error) {
-	raw, pitch, pw, ph, err := g.rawFrame(nil)
+	raw, pitch, pw, ph, err := g.rawFrame()
 	if err != nil {
 		return nil, err
 	}