signimage: circumvent 'short read' images

signimage/sign_image

@@ -385,6 +385,15 @@ if [ $(( ( copy_blocks + 2 ) % 20 )) -eq 0 ]; then
 	echo -ne "Repeating first entry as filler ... " 1>&2
 	"$YF_SIGNIMAGE_DD" if="$image_file" of="$tmp/filler.bin" bs=512 count=1 status=none 2>/dev/null
 	show_ok
+elif [ $(( copy_blocks % 8 )) -eq 5 ] || [ $(( copy_blocks % 8 )) -eq 6 ]; then
+	# Our signature would nearly fill the last 4K block and another error would get triggered
+	# (a tar file without proper EoA blocks is used by AVM, if in last 4K block only 1 or 0
+	# 512-byte blocks are free at the end - it results usually in a "short read" from tar).
+	echo -ne "Repeating first entry as filler ... " 1>&2
+	( "$YF_SIGNIMAGE_DD" if="$image_file" bs=512 count=1 status=none 2>/dev/null; \
+	"$YF_SIGNIMAGE_DD" if="$image_file" bs=512 count=1 status=none 2>/dev/null; ) \
+	> "$tmp/filler.bin"
+	show_ok
 else
 	touch "$tmp/filler.bin"
 fi