From 14ded65303fbd8bc76400ce13b0282b3a43dbcfe Mon Sep 17 00:00:00 2001
From: tonton th <sigfood@dinorama.fr>
Date: Sat, 26 Dec 2020 18:37:04 +0100
Subject: [PATCH] V4L2 : heisenbug spotted around VIDIOC_DQBUF, infinite loop

---
 v4l2/grabvidseq.c | 29 +++++++----------------------
 v4l2/notes.txt    | 17 +++++++++++++++++
 2 files changed, 24 insertions(+), 22 deletions(-)
 create mode 100644 v4l2/notes.txt

diff --git a/v4l2/grabvidseq.c b/v4l2/grabvidseq.c
index b120711..0649aed 100644
--- a/v4l2/grabvidseq.c
+++ b/v4l2/grabvidseq.c
@@ -33,7 +33,6 @@
 /*	compilation control */
 
 #define SAVE_AS_CUMUL	1
-#define SAVE_AS_PNM	0
 #define SAVE_AS_FIMG	0
 
 /* --------------------------------------------------------------------- */
@@ -190,6 +189,8 @@ if ((fmt.fmt.pix.width != width) || (fmt.fmt.pix.height != height)) {
 			    fmt.fmt.pix.width, fmt.fmt.pix.height);
 	}
 
+fprintf(stderr,"--- Ok 1\n");
+
 CLEAR(req);
 req.count = 2;
 req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
@@ -242,16 +243,14 @@ else	{
 fimg_clear(&cumul);
 cumul.fval = 255.0;		/* must be read from camera XXX */
 cumul.count = 0;
-
 to_save = &cumul;
 #endif
 
-
 type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 xioctl(fd, VIDIOC_STREAMON, &type);
 
-#if 0
-if (verbosity)	fprintf(stderr,"pid %d grabbing %d picz...\n",
+#if 1
+if (verbosity)	fprintf(stderr,"pid %d is going to grab %d picz...\n",
 					getpid(), nbre_capt);
 #endif
 
@@ -273,31 +272,17 @@ for (i = 0; i < nbre_capt; i++) {
 		}
 
 	if(verbosity > 1) {
-		printf("%6d / %6d      %9.3f\r", i, nbre_capt,
+		fprintf(stderr, "%6d / %6d      %9.3f\n", i, nbre_capt,
 						fimg_timer_get(0));
+		fflush(stderr);
 		}
 
-
 	CLEAR(buf);
 	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 	buf.memory = V4L2_MEMORY_MMAP;
 	xioctl(fd, VIDIOC_DQBUF, &buf);
 
-#if SAVE_AS_PNM
-	/* at this time,we'v got a picture in-memory,
-	   so we can blast in on storage */
-	sprintf(out_name, "%s/%05d.ppm", dest_dir, i);
-	if (verbosity > 1) fprintf(stderr, "--> %s\n", out_name);
-	fout = fopen(out_name, "w");
-	if (!fout) {
-		perror("Cannot open image");
-		exit(EXIT_FAILURE);
-		}
-	fprintf(fout, "P6\n%d %d 255\n",
-			    fmt.fmt.pix.width, fmt.fmt.pix.height);
-	fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
-	fclose(fout);
-#endif
+	fprintf(stderr, "xioctl VIDIOC_DQBUF done\n"); fflush(stderr);
 
 #if SAVE_AS_CUMUL
 	if (upscaling) {
diff --git a/v4l2/notes.txt b/v4l2/notes.txt
new file mode 100644
index 0000000..71291fa
--- /dev/null
+++ b/v4l2/notes.txt
@@ -0,0 +1,17 @@
+
+
+Heisenbug dans la capture d'image.
+
+
+	CLEAR(buf);
+	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+	buf.memory = V4L2_MEMORY_MMAP;
+	xioctl(fd, VIDIOC_DQBUF, &buf);
+
+
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE}) = -1 EAGAIN (Resource temporarily unavailable)
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE}) = -1 EAGAIN (Resource temporarily unavailable)
+ioctl(3, VIDIOC_DQBUF, {type=V4L2_BUF_TYPE_VIDEO_CAPTURE^Cstrace: Process 11181 detached
+
+
+