Loop through the read buffers to avoid getting stale frames

ChangeLog

@@ -1,3 +1,7 @@
+2010-11-07 Marc Deslauriers <marc.deslauriers@ubuntu.com>
+	* backend/v4l.c: loop through the read buffers in the v4l backend so
+	  we don't get stale frames.
+
 2010-11-06 Stéphane Voltz <stef.dev@free.fr>
 	* frontend/scanimage.c doc/scanimage.man: add -A/--all-options to list
 	all control options exposed by a backend.

backend/v4l.c

@@ -949,7 +949,7 @@ sane_get_parameters (SANE_Handle handle, SANE_Parameters * params)
 SANE_Status
 sane_start (SANE_Handle handle)
 {
-  int len;
+  int len, loop;
   V4L_Scanner *s;
 
   DBG (2, "sane_start\n");
@@ -1005,21 +1005,27 @@ sane_start (SANE_Handle handle)
       s->mmap.format = s->pict.palette;
       DBG (2, "sane_start: mmapped frame %d x %d with palette %d\n",
 	   s->mmap.width, s->mmap.height, s->mmap.format);
-      len = v4l1_ioctl (s->fd, VIDIOCMCAPTURE, &s->mmap);
+
-      if (len == -1)
+      /* We need to loop here to empty the read buffers, so we don't
-	{
+         get a stale image */
-	  DBG (1, "sane_start: ioctl VIDIOCMCAPTURE failed: %s\n",
+      for (loop = 0; loop <= s->mbuf.frames; loop++)
-	       strerror (errno));
+        {
-	  return SANE_STATUS_INVAL;
+          len = v4l1_ioctl (s->fd, VIDIOCMCAPTURE, &s->mmap);
-	}
+          if (len == -1)
-      DBG (3, "sane_start: waiting for frame %x\n", s->mmap.frame);
+	    {
-      len = v4l1_ioctl (s->fd, VIDIOCSYNC, &(s->mmap.frame));
+	      DBG (1, "sane_start: ioctl VIDIOCMCAPTURE failed: %s\n",
-      if (-1 == len)
+	           strerror (errno));
-	{
+	      return SANE_STATUS_INVAL;
-	  DBG (1, "sane_start: call to ioctl(%d, VIDIOCSYNC, ..) failed\n",
+	    }
-	       s->fd);
+          DBG (3, "sane_start: waiting for frame %x, loop %d\n", s->mmap.frame, loop);
-	  return SANE_STATUS_INVAL;
+          len = v4l1_ioctl (s->fd, VIDIOCSYNC, &(s->mmap.frame));
-	}
+          if (-1 == len)
+	    {
+	      DBG (1, "sane_start: call to ioctl(%d, VIDIOCSYNC, ..) failed\n",
+	           s->fd);
+	      return SANE_STATUS_INVAL;
+	    }
+        }
       DBG (3, "sane_start: frame %x done\n", s->mmap.frame);
     }
   DBG (3, "sane_start: done\n");