qemu-iotests: add read/write from smaller backing image test

Some image formats support backing images that are smaller than the
image file.  This patch adds a test that verifies that reads and writes
beyond the end of backing image work.

Unallocated reads beyond the end of the backing file should produce
zeroes.

Writes beyond the end of the backing file should copy-on-write using
zeroes.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

tests/qemu-iotests/028

+#!/bin/bash
+#
+# Test that backing files can be smaller than the image
+#
+# Copyright (C) 2010 IBM, Corp.
+#
+# Based on 017:
+# Copyright (C) 2009 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+# creator
+owner=stefanha@linux.vnet.ibm.com
+
+seq=`basename $0`
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+
+_cleanup()
+{
+	_cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+. ./common.pattern
+
+# Any format supporting backing files except vmdk and qcow which do not support
+# smaller backing files.
+_supported_fmt qcow2
+_supported_os Linux
+
+# Choose a size that is not necessarily a cluster size multiple for image
+# formats that use clusters.  This will ensure that the base image doesn't end
+# precisely on a cluster boundary (the easy case).
+image_size=$(( 4 * 1024 * 1024 * 1024 + 3 * 512 ))
+
+# The base image is smaller than the image file
+base_size=$(( image_size - 1024 * 1024 * 1024 ))
+
+offset=$(( base_size - 32 * 1024 ))
+
+_make_test_img $base_size
+
+echo "Filling base image"
+echo
+
+# Fill end of base image with a pattern, skipping every other sector
+io writev $offset 512 1024 31
+
+_check_test_img
+
+echo "Creating test image with backing file"
+echo
+
+mv $TEST_IMG $TEST_IMG.base
+_make_test_img -b $TEST_IMG.base $image_size
+
+echo "Filling test image"
+echo
+
+# Write every other sector around where the base image ends
+io writev $(( offset + 512 )) 512 1024 63
+
+_check_test_img
+
+echo "Reading"
+echo
+
+# Base image sectors
+io readv $(( offset )) 512 1024 31
+
+# Image sectors
+io readv $(( offset + 512 )) 512 1024 63
+
+# Zero sectors beyond end of base image
+io_zero readv $(( offset + 32 * 1024 )) 512 1024 31
+
+_check_test_img
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0

tests/qemu-iotests/group

@@ -34,3 +34,4 @@
 025 rw auto
 026 rw blkdbg auto
 027 rw auto
+028 rw backing auto