iotests: Test convert -n -B to backing-less target

This must not crash.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200121155915.98232-3-mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/122

@@ -276,6 +276,20 @@ $QEMU_IMG convert -O $IMGFMT -n "$TEST_IMG" "$TEST_IMG".orig
 
 $QEMU_IMG compare "$TEST_IMG" "$TEST_IMG".orig
 
+echo
+echo '=== -n -B to an image without a backing file ==='
+echo
+
+# Base for the output
+TEST_IMG="$TEST_IMG".base _make_test_img 64M
+
+# Output that does have $TEST_IMG.base set as its (implicit) backing file
+TEST_IMG="$TEST_IMG".orig _make_test_img 64M
+
+# Convert with -n, which should not confuse -B with "target BDS has a
+# backing file"
+$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base -n "$TEST_IMG" "$TEST_IMG".orig
+
 # success, all done
 echo '*** done'
 rm -f $seq.full

tests/qemu-iotests/122.out

@@ -228,4 +228,9 @@ Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=67108864
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Images are identical.
+
+=== -n -B to an image without a backing file ===
+
+Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
+Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=67108864
 *** done