tests/qemu-iotests/108 - third_party/qemu - Git at Google

 #!/usr/bin/env bash
 # group: rw auto quick
 #
 # Test case for repairing qcow2 images which cannot be repaired using
 # the on-disk refcount structures
 #
 # Copyright (C) 2014 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=hreitz@redhat.com

 seq="$(basename $0)"
 echo "QA output created by $seq"

 status=1	# failure is the default!

 _cleanup()
 {
     _cleanup_test_img
     if [ -f "$TEST_DIR/qsd.pid" ]; then
         qsd_pid=$(cat "$TEST_DIR/qsd.pid")
         kill -KILL "$qsd_pid"
         fusermount -u "$TEST_DIR/fuse-export" &>/dev/null
     fi
     rm -f "$TEST_DIR/fuse-export"
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15

 # get standard environment, filters and checks
 . ./common.rc
 . ./common.filter
 . ./common.qemu

 # This tests qcow2-specific low-level functionality
 _supported_fmt qcow2
 _supported_proto file fuse
 _supported_os Linux
 # This test directly modifies a refblock so it relies on refcount_bits being 16;
 # and the low-level modification it performs are not tuned for external data
 # files
 _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file

 # This test either needs sudo -n losetup or FUSE exports to work
 if sudo -n losetup &>/dev/null; then
     loopdev=true
 else
     loopdev=false

     # Check for usable FUSE in the host environment:
     if test ! -c "/dev/fuse"; then
         _notrun 'No passwordless sudo nor usable /dev/fuse'
     fi

     # QSD --export fuse will either yield "Parameter 'id' is missing"
     # or "Invalid parameter 'fuse'", depending on whether there is
     # FUSE support or not.
     error=$($QSD --export fuse 2>&1)
     if [[ $error = *"'fuse'"* ]]; then
         _notrun 'Passwordless sudo for losetup or FUSE support required, but' \
                 'neither is available'
     fi
 fi

 echo
 echo '=== Repairing an image without any refcount table ==='
 echo

 _make_test_img 64M
 # just write some data
 $QEMU_IO -c 'write -P 42 0 64k' "$TEST_IMG" | _filter_qemu_io

 # refcount_table_offset
 poke_file "$TEST_IMG" $((0x30)) "\x00\x00\x00\x00\x00\x00\x00\x00"
 # refcount_table_clusters
 poke_file "$TEST_IMG" $((0x38)) "\x00\x00\x00\x00"

 _check_test_img -r all

 $QEMU_IO -c 'read -P 42 0 64k' "$TEST_IMG" | _filter_qemu_io

 echo
 echo '=== Repairing unreferenced data cluster in new refblock area ==='
 echo

 _make_test_img -o 'cluster_size=512' 64M
 # Allocate the first 128 kB in the image (first refblock)
 $QEMU_IO -c 'write 0 0x1b200' "$TEST_IMG" | _filter_qemu_io
 # should be 131072 == 0x20000
 stat -c '%s' "$TEST_IMG"

 # Enter a cluster at 128 kB (0x20000)
 # XXX: This should be the first free entry in the last L2 table, but we cannot
 # be certain
 poke_file "$TEST_IMG" $((0x1ccc8)) "\x80\x00\x00\x00\x00\x02\x00\x00"

 # Fill the cluster
 truncate -s $((0x20200)) "$TEST_IMG"
 $QEMU_IO -c "open -o driver=raw $TEST_IMG" -c 'write -P 42 128k 512' \
     | _filter_qemu_io

 # The data should now appear at this guest offset
 $QEMU_IO -c 'read -P 42 0x1b200 512' "$TEST_IMG" | _filter_qemu_io

 # This cluster is unallocated; fix it
 _check_test_img -r all

 # This repair operation must have allocated a new refblock; and that refblock
 # should not overlap with the unallocated data cluster. If it does, the data
 # will be damaged, so check it.
 $QEMU_IO -c 'read -P 42 0x1b200 512' "$TEST_IMG" | _filter_qemu_io

 echo
 echo '=== Repairing refblock beyond the image end ==='
 echo

 echo
 echo '--- Otherwise clean ---'
 echo

 _make_test_img 64M
 # Normally, qemu doesn't create empty refblocks, so we just have to do it by
 # hand
 # XXX: This should be the entry for the second refblock
 poke_file "$TEST_IMG" $((0x10008)) "\x00\x00\x00\x00\x00\x10\x00\x00"
 # Mark that refblock as used
 # XXX: This should be the 17th entry (cluster 16) of the first
 # refblock
 poke_file "$TEST_IMG" $((0x20020)) "\x00\x01"
 _check_test_img -r all

 echo
 echo '--- Refblock is unallocated ---'
 echo

 _make_test_img 64M
 poke_file "$TEST_IMG" $((0x10008)) "\x00\x00\x00\x00\x00\x10\x00\x00"
 _check_test_img -r all

 echo
 echo '--- Signed overflow after the refblock ---'
 echo

 _make_test_img 64M
 poke_file "$TEST_IMG" $((0x10008)) "\x7f\xff\xff\xff\xff\xff\x00\x00"
 _check_test_img -r all

 echo
 echo '--- Unsigned overflow after the refblock ---'
 echo

 _make_test_img 64M
 poke_file "$TEST_IMG" $((0x10008)) "\xff\xff\xff\xff\xff\xff\x00\x00"
 _check_test_img -r all

 echo
 echo '=== Check rebuilt reftable location ==='

 # In an earlier version of the refcount rebuild algorithm, the
 # reftable was generally placed at the image end (unless something was
 # allocated in the area covered by the refblock right before the image
 # file end, then we would try to place the reftable in that refblock).
 # This was later changed so the reftable would be placed in the
 # earliest possible location.  Test this.

 echo
 echo '--- Does the image size increase? ---'
 echo

 # First test: Just create some image, write some data to it, and
 # resize it so there is free space at the end of the image (enough
 # that it spans at least one full refblock, which for cluster_size=512
 # images, spans 128k).  With the old algorithm, the reftable would
 # have then been placed at the end of the image file, but with the new
 # one, it will be put in that free space.
 # We want to check whether the size of the image file increases due to
 # rebuilding the refcount structures (it should not).

 _make_test_img -o 'cluster_size=512' 1M
 # Write something
 $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io

 # Add free space
 file_len=$(stat -c '%s' "$TEST_IMG")
 truncate -s $((file_len + 256 * 1024)) "$TEST_IMG"

 # Corrupt the image by saying the image header was not allocated
 rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
 rb_offset=$(peek_file_be "$TEST_IMG" $rt_offset 8)
 poke_file "$TEST_IMG" $rb_offset "\x00\x00"

 # Check whether rebuilding the refcount structures increases the image
 # file size
 file_len=$(stat -c '%s' "$TEST_IMG")
 echo
 # The only leaks there can be are the old refcount structures that are
 # leaked during rebuilding, no need to clutter the output with them
 _check_test_img -r all | grep -v '^Repairing cluster.*refcount=1 reference=0'
 echo
 post_repair_file_len=$(stat -c '%s' "$TEST_IMG")

 if [[ $file_len -eq $post_repair_file_len ]]; then
     echo 'OK: Image size did not change'
 else
     echo 'ERROR: Image size differs' \
         "($file_len before, $post_repair_file_len after)"
 fi

 echo
 echo '--- Will the reftable occupy a hole specifically left for it?  ---'
 echo

 # Note: With cluster_size=512, every refblock covers 128k.
 # The reftable covers 8M per reftable cluster.

 # Create an image that requires two reftable clusters (just because
 # this is more interesting than a single-clustered reftable).
 _make_test_img -o 'cluster_size=512' 9M
 $QEMU_IO -c 'write 0 8M' "$TEST_IMG" | _filter_qemu_io

 # Writing 8M will have resized the reftable.  Unfortunately, doing so
 # will leave holes in the file, so we need to fill them up so we can
 # be sure the whole file is allocated.  Do that by writing
 # consecutively smaller chunks starting from 8 MB, until the file
 # length increases even with a chunk size of 512.  Then we must have
 # filled all holes.
 ofs=$((8 * 1024 * 1024))
 block_len=$((16 * 1024))
 while [[ $block_len -ge 512 ]]; do
     file_len=$(stat -c '%s' "$TEST_IMG")
     while [[ $(stat -c '%s' "$TEST_IMG") -eq $file_len ]]; do
         # Do not include this in the reference output, it does not
         # really matter which qemu-io calls we do here exactly
         $QEMU_IO -c "write $ofs $block_len" "$TEST_IMG" >/dev/null
         ofs=$((ofs + block_len))
     done
     block_len=$((block_len / 2))
 done

 # Fill up to 9M (do not include this in the reference output either,
 # $ofs is random for all we know)
 $QEMU_IO -c "write $ofs $((9 * 1024 * 1024 - ofs))" "$TEST_IMG" >/dev/null

 # Make space as follows:
 # - For the first refblock: Right at the beginning of the image (this
 #   refblock is placed in the first place possible),
 # - For the reftable somewhere soon afterwards, still near the
 #   beginning of the image (i.e. covered by the first refblock); the
 #   reftable too is placed in the first place possible, but only after
 #   all refblocks have been placed)
 # No space is needed for the other refblocks, because no refblock is
 # put before the space it covers.  In this test case, we do not mind
 # if they are placed at the image file's end.

 # Before we make that space, we have to find out the host offset of
 # the area that belonged to the two data clusters at guest offset 4k,
 # because we expect the reftable to be placed there, and we will have
 # to verify that it is.

 l1_offset=$(peek_file_be "$TEST_IMG" 40 8)
 l2_offset=$(peek_file_be "$TEST_IMG" $l1_offset 8)
 l2_offset=$((l2_offset & 0x00fffffffffffe00))
 data_4k_offset=$(peek_file_be "$TEST_IMG" \
                  $((l2_offset + 4096 / 512 * 8)) 8)
 data_4k_offset=$((data_4k_offset & 0x00fffffffffffe00))

 $QEMU_IO -c "discard 0 512" -c "discard 4k 1k" "$TEST_IMG" | _filter_qemu_io

 # Corrupt the image by saying the image header was not allocated
 rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
 rb_offset=$(peek_file_be "$TEST_IMG" $rt_offset 8)
 poke_file "$TEST_IMG" $rb_offset "\x00\x00"

 echo
 # The only leaks there can be are the old refcount structures that are
 # leaked during rebuilding, no need to clutter the output with them
 _check_test_img -r all | grep -v '^Repairing cluster.*refcount=1 reference=0'
 echo

 # Check whether the reftable was put where we expected
 rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
 if [[ $rt_offset -eq $data_4k_offset ]]; then
     echo 'OK: Reftable is where we expect it'
 else
     echo "ERROR: Reftable is at $rt_offset, but was expected at $data_4k_offset"
 fi

 echo
 echo '--- Rebuilding refcount structures on block devices ---'
 echo

 # A block device cannot really grow, at least not during qemu-img
 # check.  As mentioned in the above cases, rebuilding the refcount
 # structure may lead to new refcount structures being written after
 # the end of the image, and in the past that happened even if there
 # was more than sufficient space in the image.  Such post-EOF writes
 # will not work on block devices, so test that the new algorithm
 # avoids it.

 # If we have passwordless sudo and losetup, we can use those to create
 # a block device.  Otherwise, we can resort to qemu's FUSE export to
 # create a file that isn't growable, which effectively tests the same
 # thing.

 _cleanup_test_img
 truncate -s $((64 * 1024 * 1024)) "$TEST_IMG"

 if $loopdev; then
     export_mp=$(sudo -n losetup --show -f "$TEST_IMG")
     export_mp_driver=host_device
     sudo -n chmod go+rw "$export_mp"
 else
     # Create non-growable FUSE export that is a bit like an empty
     # block device
     export_mp="$TEST_DIR/fuse-export"
     export_mp_driver=file
     touch "$export_mp"

     $QSD \
         --blockdev file,node-name=export-node,filename="$TEST_IMG" \
         --export fuse,id=fuse-export,node-name=export-node,mountpoint="$export_mp",writable=on,growable=off,allow-other=off \
         --pidfile "$TEST_DIR/qsd.pid" \
         --daemonize
 fi

 # Now create a qcow2 image on the device -- unfortunately, qemu-img
 # create force-creates the file, so we have to resort to the
 # blockdev-create job.
 _launch_qemu \
     --blockdev $export_mp_driver,node-name=file,filename="$export_mp"

 _send_qemu_cmd \
     $QEMU_HANDLE \
     '{ "execute": "qmp_capabilities" }' \
     'return'

 # Small cluster size again, so the image needs multiple refblocks
 _send_qemu_cmd \
     $QEMU_HANDLE \
     '{ "execute": "blockdev-create",
        "arguments": {
            "job-id": "create",
            "options": {
                "driver": "qcow2",
                "file": "file",
                "size": '$((64 * 1024 * 1024))',
                "cluster-size": 512
            } } }' \
     '"concluded"'

 _send_qemu_cmd \
     $QEMU_HANDLE \
     '{ "execute": "job-dismiss", "arguments": { "id": "create" } }' \
     'return'

 _send_qemu_cmd \
     $QEMU_HANDLE \
     '{ "execute": "quit" }' \
     'return'

 wait=y _cleanup_qemu
 echo

 # Write some data
 $QEMU_IO -c 'write 0 64k' "$export_mp" | _filter_qemu_io

 # Corrupt the image by saying the image header was not allocated
 rt_offset=$(peek_file_be "$export_mp" 48 8)
 rb_offset=$(peek_file_be "$export_mp" $rt_offset 8)
 poke_file "$export_mp" $rb_offset "\x00\x00"

 # Repairing such a simple case should just work
 # (We used to put the reftable at the end of the image file, which can
 # never work for non-growable devices.)
 echo
 TEST_IMG="$export_mp" _check_test_img -r all \
     | grep -v '^Repairing cluster.*refcount=1 reference=0'

 if $loopdev; then
     sudo -n losetup -d "$export_mp"
 else
     qsd_pid=$(cat "$TEST_DIR/qsd.pid")
     kill -TERM "$qsd_pid"
     # Wait for process to exit (cannot `wait` because the QSD is daemonized)
     while [ -f "$TEST_DIR/qsd.pid" ]; do
         true
     done
 fi

 # success, all done
 echo '*** done'
 rm -f $seq.full
 status=0
	#!/usr/bin/env bash
	# group: rw auto quick
	#
	# Test case for repairing qcow2 images which cannot be repaired using
	# the on-disk refcount structures
	#
	# Copyright (C) 2014 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=hreitz@redhat.com

	seq="$(basename $0)"
	echo "QA output created by $seq"

	status=1 # failure is the default!

	_cleanup()
	{
	_cleanup_test_img
	if [ -f "$TEST_DIR/qsd.pid" ]; then
	qsd_pid=$(cat "$TEST_DIR/qsd.pid")
	kill -KILL "$qsd_pid"
	fusermount -u "$TEST_DIR/fuse-export" &>/dev/null
	fi
	rm -f "$TEST_DIR/fuse-export"
	}
	trap "_cleanup; exit \$status" 0 1 2 3 15

	# get standard environment, filters and checks
	. ./common.rc
	. ./common.filter
	. ./common.qemu

	# This tests qcow2-specific low-level functionality
	_supported_fmt qcow2
	_supported_proto file fuse
	_supported_os Linux
	# This test directly modifies a refblock so it relies on refcount_bits being 16;
	# and the low-level modification it performs are not tuned for external data
	# files
	_unsupported_imgopts 'refcount_bits=\([^1]\\|.\([^6]\\|$\)\)' data_file

	# This test either needs sudo -n losetup or FUSE exports to work
	if sudo -n losetup &>/dev/null; then
	loopdev=true
	else
	loopdev=false

	# Check for usable FUSE in the host environment:
	if test ! -c "/dev/fuse"; then
	_notrun 'No passwordless sudo nor usable /dev/fuse'
	fi

	# QSD --export fuse will either yield "Parameter 'id' is missing"
	# or "Invalid parameter 'fuse'", depending on whether there is
	# FUSE support or not.
	error=$($QSD --export fuse 2>&1)
	if [[ $error = "'fuse'" ]]; then
	_notrun 'Passwordless sudo for losetup or FUSE support required, but' \
	'neither is available'
	fi
	fi

	echo
	echo '=== Repairing an image without any refcount table ==='
	echo

	_make_test_img 64M
	# just write some data
	$QEMU_IO -c 'write -P 42 0 64k' "$TEST_IMG" \| _filter_qemu_io

	# refcount_table_offset
	poke_file "$TEST_IMG" $((0x30)) "\x00\x00\x00\x00\x00\x00\x00\x00"
	# refcount_table_clusters
	poke_file "$TEST_IMG" $((0x38)) "\x00\x00\x00\x00"

	_check_test_img -r all

	$QEMU_IO -c 'read -P 42 0 64k' "$TEST_IMG" \| _filter_qemu_io

	echo
	echo '=== Repairing unreferenced data cluster in new refblock area ==='
	echo

	_make_test_img -o 'cluster_size=512' 64M
	# Allocate the first 128 kB in the image (first refblock)
	$QEMU_IO -c 'write 0 0x1b200' "$TEST_IMG" \| _filter_qemu_io
	# should be 131072 == 0x20000
	stat -c '%s' "$TEST_IMG"

	# Enter a cluster at 128 kB (0x20000)
	# XXX: This should be the first free entry in the last L2 table, but we cannot
	# be certain
	poke_file "$TEST_IMG" $((0x1ccc8)) "\x80\x00\x00\x00\x00\x02\x00\x00"

	# Fill the cluster
	truncate -s $((0x20200)) "$TEST_IMG"
	$QEMU_IO -c "open -o driver=raw $TEST_IMG" -c 'write -P 42 128k 512' \
	\| _filter_qemu_io

	# The data should now appear at this guest offset
	$QEMU_IO -c 'read -P 42 0x1b200 512' "$TEST_IMG" \| _filter_qemu_io

	# This cluster is unallocated; fix it
	_check_test_img -r all

	# This repair operation must have allocated a new refblock; and that refblock
	# should not overlap with the unallocated data cluster. If it does, the data
	# will be damaged, so check it.
	$QEMU_IO -c 'read -P 42 0x1b200 512' "$TEST_IMG" \| _filter_qemu_io

	echo
	echo '=== Repairing refblock beyond the image end ==='
	echo

	echo
	echo '--- Otherwise clean ---'
	echo

	_make_test_img 64M
	# Normally, qemu doesn't create empty refblocks, so we just have to do it by
	# hand
	# XXX: This should be the entry for the second refblock
	poke_file "$TEST_IMG" $((0x10008)) "\x00\x00\x00\x00\x00\x10\x00\x00"
	# Mark that refblock as used
	# XXX: This should be the 17th entry (cluster 16) of the first
	# refblock
	poke_file "$TEST_IMG" $((0x20020)) "\x00\x01"
	_check_test_img -r all

	echo
	echo '--- Refblock is unallocated ---'
	echo

	_make_test_img 64M
	poke_file "$TEST_IMG" $((0x10008)) "\x00\x00\x00\x00\x00\x10\x00\x00"
	_check_test_img -r all

	echo
	echo '--- Signed overflow after the refblock ---'
	echo

	_make_test_img 64M
	poke_file "$TEST_IMG" $((0x10008)) "\x7f\xff\xff\xff\xff\xff\x00\x00"
	_check_test_img -r all

	echo
	echo '--- Unsigned overflow after the refblock ---'
	echo

	_make_test_img 64M
	poke_file "$TEST_IMG" $((0x10008)) "\xff\xff\xff\xff\xff\xff\x00\x00"
	_check_test_img -r all

	echo
	echo '=== Check rebuilt reftable location ==='

	# In an earlier version of the refcount rebuild algorithm, the
	# reftable was generally placed at the image end (unless something was
	# allocated in the area covered by the refblock right before the image
	# file end, then we would try to place the reftable in that refblock).
	# This was later changed so the reftable would be placed in the
	# earliest possible location. Test this.

	echo
	echo '--- Does the image size increase? ---'
	echo

	# First test: Just create some image, write some data to it, and
	# resize it so there is free space at the end of the image (enough
	# that it spans at least one full refblock, which for cluster_size=512
	# images, spans 128k). With the old algorithm, the reftable would
	# have then been placed at the end of the image file, but with the new
	# one, it will be put in that free space.
	# We want to check whether the size of the image file increases due to
	# rebuilding the refcount structures (it should not).

	_make_test_img -o 'cluster_size=512' 1M
	# Write something
	$QEMU_IO -c 'write 0 64k' "$TEST_IMG" \| _filter_qemu_io

	# Add free space
	file_len=$(stat -c '%s' "$TEST_IMG")
	truncate -s $((file_len + 256 * 1024)) "$TEST_IMG"

	# Corrupt the image by saying the image header was not allocated
	rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
	rb_offset=$(peek_file_be "$TEST_IMG" $rt_offset 8)
	poke_file "$TEST_IMG" $rb_offset "\x00\x00"

	# Check whether rebuilding the refcount structures increases the image
	# file size
	file_len=$(stat -c '%s' "$TEST_IMG")
	echo
	# The only leaks there can be are the old refcount structures that are
	# leaked during rebuilding, no need to clutter the output with them
	_check_test_img -r all \| grep -v '^Repairing cluster.*refcount=1 reference=0'
	echo
	post_repair_file_len=$(stat -c '%s' "$TEST_IMG")

	if [[ $file_len -eq $post_repair_file_len ]]; then
	echo 'OK: Image size did not change'
	else
	echo 'ERROR: Image size differs' \
	"($file_len before, $post_repair_file_len after)"
	fi

	echo
	echo '--- Will the reftable occupy a hole specifically left for it? ---'
	echo

	# Note: With cluster_size=512, every refblock covers 128k.
	# The reftable covers 8M per reftable cluster.

	# Create an image that requires two reftable clusters (just because
	# this is more interesting than a single-clustered reftable).
	_make_test_img -o 'cluster_size=512' 9M
	$QEMU_IO -c 'write 0 8M' "$TEST_IMG" \| _filter_qemu_io

	# Writing 8M will have resized the reftable. Unfortunately, doing so
	# will leave holes in the file, so we need to fill them up so we can
	# be sure the whole file is allocated. Do that by writing
	# consecutively smaller chunks starting from 8 MB, until the file
	# length increases even with a chunk size of 512. Then we must have
	# filled all holes.
	ofs=$((8 * 1024 * 1024))
	block_len=$((16 * 1024))
	while [[ $block_len -ge 512 ]]; do
	file_len=$(stat -c '%s' "$TEST_IMG")
	while [[ $(stat -c '%s' "$TEST_IMG") -eq $file_len ]]; do
	# Do not include this in the reference output, it does not
	# really matter which qemu-io calls we do here exactly
	$QEMU_IO -c "write $ofs $block_len" "$TEST_IMG" >/dev/null
	ofs=$((ofs + block_len))
	done
	block_len=$((block_len / 2))
	done

	# Fill up to 9M (do not include this in the reference output either,
	# $ofs is random for all we know)
	$QEMU_IO -c "write $ofs $((9 * 1024 * 1024 - ofs))" "$TEST_IMG" >/dev/null

	# Make space as follows:
	# - For the first refblock: Right at the beginning of the image (this
	# refblock is placed in the first place possible),
	# - For the reftable somewhere soon afterwards, still near the
	# beginning of the image (i.e. covered by the first refblock); the
	# reftable too is placed in the first place possible, but only after
	# all refblocks have been placed)
	# No space is needed for the other refblocks, because no refblock is
	# put before the space it covers. In this test case, we do not mind
	# if they are placed at the image file's end.

	# Before we make that space, we have to find out the host offset of
	# the area that belonged to the two data clusters at guest offset 4k,
	# because we expect the reftable to be placed there, and we will have
	# to verify that it is.

	l1_offset=$(peek_file_be "$TEST_IMG" 40 8)
	l2_offset=$(peek_file_be "$TEST_IMG" $l1_offset 8)
	l2_offset=$((l2_offset & 0x00fffffffffffe00))
	data_4k_offset=$(peek_file_be "$TEST_IMG" \
	$((l2_offset + 4096 / 512 * 8)) 8)
	data_4k_offset=$((data_4k_offset & 0x00fffffffffffe00))

	$QEMU_IO -c "discard 0 512" -c "discard 4k 1k" "$TEST_IMG" \| _filter_qemu_io

	# Corrupt the image by saying the image header was not allocated
	rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
	rb_offset=$(peek_file_be "$TEST_IMG" $rt_offset 8)
	poke_file "$TEST_IMG" $rb_offset "\x00\x00"

	echo
	# The only leaks there can be are the old refcount structures that are
	# leaked during rebuilding, no need to clutter the output with them
	_check_test_img -r all \| grep -v '^Repairing cluster.*refcount=1 reference=0'
	echo

	# Check whether the reftable was put where we expected
	rt_offset=$(peek_file_be "$TEST_IMG" 48 8)
	if [[ $rt_offset -eq $data_4k_offset ]]; then
	echo 'OK: Reftable is where we expect it'
	else
	echo "ERROR: Reftable is at $rt_offset, but was expected at $data_4k_offset"
	fi

	echo
	echo '--- Rebuilding refcount structures on block devices ---'
	echo

	# A block device cannot really grow, at least not during qemu-img
	# check. As mentioned in the above cases, rebuilding the refcount
	# structure may lead to new refcount structures being written after
	# the end of the image, and in the past that happened even if there
	# was more than sufficient space in the image. Such post-EOF writes
	# will not work on block devices, so test that the new algorithm
	# avoids it.

	# If we have passwordless sudo and losetup, we can use those to create
	# a block device. Otherwise, we can resort to qemu's FUSE export to
	# create a file that isn't growable, which effectively tests the same
	# thing.

	_cleanup_test_img
	truncate -s $((64 * 1024 * 1024)) "$TEST_IMG"

	if $loopdev; then
	export_mp=$(sudo -n losetup --show -f "$TEST_IMG")
	export_mp_driver=host_device
	sudo -n chmod go+rw "$export_mp"
	else
	# Create non-growable FUSE export that is a bit like an empty
	# block device
	export_mp="$TEST_DIR/fuse-export"
	export_mp_driver=file
	touch "$export_mp"

	$QSD \
	--blockdev file,node-name=export-node,filename="$TEST_IMG" \
	--export fuse,id=fuse-export,node-name=export-node,mountpoint="$export_mp",writable=on,growable=off,allow-other=off \
	--pidfile "$TEST_DIR/qsd.pid" \
	--daemonize
	fi

	# Now create a qcow2 image on the device -- unfortunately, qemu-img
	# create force-creates the file, so we have to resort to the
	# blockdev-create job.
	_launch_qemu \
	--blockdev $export_mp_driver,node-name=file,filename="$export_mp"

	_send_qemu_cmd \
	$QEMU_HANDLE \
	'{ "execute": "qmp_capabilities" }' \
	'return'

	# Small cluster size again, so the image needs multiple refblocks
	_send_qemu_cmd \
	$QEMU_HANDLE \
	'{ "execute": "blockdev-create",
	"arguments": {
	"job-id": "create",
	"options": {
	"driver": "qcow2",
	"file": "file",
	"size": '$((64 * 1024 * 1024))',
	"cluster-size": 512
	} } }' \
	'"concluded"'

	_send_qemu_cmd \
	$QEMU_HANDLE \
	'{ "execute": "job-dismiss", "arguments": { "id": "create" } }' \
	'return'

	_send_qemu_cmd \
	$QEMU_HANDLE \
	'{ "execute": "quit" }' \
	'return'

	wait=y _cleanup_qemu
	echo

	# Write some data
	$QEMU_IO -c 'write 0 64k' "$export_mp" \| _filter_qemu_io

	# Corrupt the image by saying the image header was not allocated
	rt_offset=$(peek_file_be "$export_mp" 48 8)
	rb_offset=$(peek_file_be "$export_mp" $rt_offset 8)
	poke_file "$export_mp" $rb_offset "\x00\x00"

	# Repairing such a simple case should just work
	# (We used to put the reftable at the end of the image file, which can
	# never work for non-growable devices.)
	echo
	TEST_IMG="$export_mp" _check_test_img -r all \
	\| grep -v '^Repairing cluster.*refcount=1 reference=0'

	if $loopdev; then
	sudo -n losetup -d "$export_mp"
	else
	qsd_pid=$(cat "$TEST_DIR/qsd.pid")
	kill -TERM "$qsd_pid"
	# Wait for process to exit (cannot `wait` because the QSD is daemonized)
	while [ -f "$TEST_DIR/qsd.pid" ]; do
	true
	done
	fi

	# success, all done
	echo '*** done'
	rm -f $seq.full
	status=0