--- zbar-0.10/zbar/video/v4l2.c	2009-10-23 18:16:44.000000000 +0000
+++ zbar-0.10/zbar/video/v4l2.c	2015-03-07 05:46:36.000000000 +0000
@@ -241,6 +241,21 @@
     return(0);
 }
 
+static int v4l2_request_buffers (zbar_video_t *vdo)
+{
+    struct v4l2_requestbuffers rb;
+    memset(&rb, 0, sizeof(rb));
+    rb.count = vdo->num_images;
+    rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    rb.memory = V4L2_MEMORY_USERPTR;
+    if(ioctl(vdo->fd, VIDIOC_REQBUFS, &rb) < 0)
+        return(err_capture(vdo, SEV_ERROR, ZBAR_ERR_SYSTEM, __func__,
+                           "requesting video frame buffers (VIDIOC_REQBUFS)"));
+    if(rb.count) 
+        vdo->num_images = rb.count;
+    return(0);
+}
+
 static int v4l2_set_format (zbar_video_t *vdo,
                             uint32_t fmt)
 {
@@ -308,6 +323,8 @@
         return(-1);
     if(vdo->iomode == VIDEO_MMAP)
         return(v4l2_mmap_buffers(vdo));
+    if(vdo->iomode == VIDEO_USERPTR)
+        return(v4l2_request_buffers(vdo));
     return(0);
 }
 
@@ -337,8 +354,13 @@
     else {
         if(!vdo->iomode)
             vdo->iomode = VIDEO_USERPTR;
-        if(rb.count)
-            vdo->num_images = rb.count;
+        /* releasing buffers 
+         * lest the driver may later refuse to change format
+         */
+        rb.count = 0;
+        if (ioctl(vdo->fd, VIDIOC_REQBUFS, &rb) < 0)
+            zprintf(0, "WARNING: releasing video buffers failed: error %d\n",
+                errno);
     }
     return(0);
 }