block: Update BlockDriverState.inherits_from on bdrv_set_backing_hd()

When a BlockDriverState's child is opened (be it a backing file, the
protocol layer, or any other) inherits_from is set to point to the
parent node. Children opened separately and then attached to a parent
don't have this pointer set.

bdrv_reopen_queue_child() uses this to determine whether a node's
children must also be reopened inheriting the options from the parent
or not. If inherits_from points to the parent then the child is
reopened and its options can be changed, like in this example:

   $ qemu-img create -f qcow2 hd0.qcow2 1M
   $ qemu-img create -f qcow2 hd1.qcow2 1M
   $ $QEMU -drive if=none,node-name=hd0,file=hd0.qcow2,\
                  backing.driver=qcow2,backing.file.filename=hd1.qcow2
   (qemu) qemu-io hd0 "reopen -o backing.l2-cache-size=2M"

If the child does not inherit from the parent then it does not get
reopened and its options cannot be changed:

   $ $QEMU -drive if=none,node-name=hd1,file=hd1.qcow2
           -drive if=none,node-name=hd0,file=hd0.qcow2,backing=hd1
   (qemu) qemu-io hd0 "reopen -o backing.l2-cache-size=2M"
   Cannot change the option 'backing.l2-cache-size'

If a disk image has a chain of backing files then all of them are also
connected through their inherits_from pointers (i.e. it's possible to
walk the chain in reverse order from base to top).

However this is broken if the intermediate nodes are removed using
e.g. block-stream because the inherits_from pointer from the base node
becomes NULL:

   $ qemu-img create -f qcow2 hd0.qcow2 1M
   $ qemu-img create -f qcow2 -b hd0.qcow2 hd1.qcow2
   $ qemu-img create -f qcow2 -b hd1.qcow2 hd2.qcow2
   $ $QEMU -drive if=none,file=hd2.qcow2
   (qemu) qemu-io none0 "reopen -o backing.l2-cache-size=2M"
   (qemu) block_stream none0 0 hd0.qcow2
   (qemu) qemu-io none0 "reopen -o backing.l2-cache-size=2M"
   Cannot change the option 'backing.l2-cache-size'

This patch updates the inherits_from pointer if the intermediate nodes
of a backing chain are removed using bdrv_set_backing_hd(), and adds a
test case for this scenario.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 104 insertions, 0 deletions

diff --git a/tests/qemu-iotests/161 b/tests/qemu-iotests/161
new file mode 100755
index 0000000000..8d0c6afb47
--- /dev/null
+++ b/tests/qemu-iotests/161
@@ -0,0 +1,104 @@
+#!/bin/bash
+#
+# Test reopening a backing image after block-stream
+#
+# Copyright (C) 2018 Igalia, S.L.
+#
+# 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=berto@igalia.com
+
+seq=`basename $0`
+echo "QA output created by $seq"
+
+here=`pwd`
+status=1	# failure is the default!
+
+_cleanup()
+{
+    _cleanup_test_img
+    rm -f "$TEST_IMG.base"
+    rm -f "$TEST_IMG.int"
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+. ./common.qemu
+
+# Any format implementing BlockDriver.bdrv_change_backing_file
+_supported_fmt qcow2 qed
+_supported_proto file
+_supported_os Linux
+
+IMG_SIZE=1M
+
+# Create the images
+TEST_IMG="$TEST_IMG.base" _make_test_img $IMG_SIZE | _filter_imgfmt
+TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" | _filter_imgfmt
+_make_test_img -b "$TEST_IMG.int" | _filter_imgfmt
+
+# First test: reopen $TEST.IMG changing the detect-zeroes option on
+# its backing file ($TEST_IMG.int).
+echo
+echo "*** Change an option on the backing file"
+echo
+_launch_qemu -drive if=none,file="${TEST_IMG}"
+_send_qemu_cmd $QEMU_HANDLE \
+    "{ 'execute': 'qmp_capabilities' }" \
+    'return'
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{ 'execute': 'human-monitor-command',
+       'arguments': { 'command-line':
+                      'qemu-io none0 \"reopen -o backing.detect-zeroes=on\"' } }" \
+    "return"
+
+_cleanup_qemu
+
+# Second test: stream $TEST_IMG.base into $TEST_IMG.int and then
+# reopen $TEST.IMG changing the detect-zeroes option on its new
+# backing file ($TEST_IMG.base).
+echo
+echo "*** Stream and then change an option on the backing file"
+echo
+_launch_qemu -drive if=none,file="${TEST_IMG}"
+_send_qemu_cmd $QEMU_HANDLE \
+    "{ 'execute': 'qmp_capabilities' }" \
+    'return'
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{ 'execute': 'block-stream', \
+       'arguments': { 'device': 'none0',
+                      'base': '${TEST_IMG}.base' } }" \
+    'return'
+
+# Wait for block-stream to finish
+sleep 0.5
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{ 'execute': 'human-monitor-command',
+       'arguments': { 'command-line':
+                      'qemu-io none0 \"reopen -o backing.detect-zeroes=on\"' } }" \
+    "return"
+
+_cleanup_qemu
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0