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block: Update BlockDriverState.inherits_from on bdrv_set_backing_hd()

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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>
This commit is contained in:
Alberto Garcia 2018-10-31 18:16:37 +02:00 committed by Kevin Wolf
parent a237dea330
commit 0065c455f9
4 changed files with 149 additions and 0 deletions
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21
block.c
View File

@ -2260,6 +2260,18 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load)
}
}
/* Return true if you can reach parent going through child->inherits_from
* recursively. If parent or child are NULL, return false */
static bool bdrv_inherits_from_recursive(BlockDriverState *child,
BlockDriverState *parent)
{
while (child && child != parent) {
child = child->inherits_from;
}
return child != NULL;
}
/*
* Sets the backing file link of a BDS. A new reference is created; callers
* which don't need their own reference any more must call bdrv_unref().
@ -2267,6 +2279,9 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load)
void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
Error **errp)
{
bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
bdrv_inherits_from_recursive(backing_hd, bs);
if (backing_hd) {
bdrv_ref(backing_hd);
}
@ -2282,6 +2297,12 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing,
errp);
/* If backing_hd was already part of bs's backing chain, and
* inherits_from pointed recursively to bs then let's update it to
* point directly to bs (else it will become NULL). */
if (update_inherits_from) {
backing_hd->inherits_from = bs;
}
if (!bs->backing) {
bdrv_unref(backing_hd);
}

104
tests/qemu-iotests/161 Executable file
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@ -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

23
tests/qemu-iotests/161.out Normal file
View File

@ -0,0 +1,23 @@
QA output created by 161
Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int
*** Change an option on the backing file
{"return": {}}
{"return": ""}
*** Stream and then change an option on the backing file
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "created", "id": "none0"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "none0"}}
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "waiting", "id": "none0"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "pending", "id": "none0"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_JOB_COMPLETED", "data": {"device": "none0", "len": 1048576, "offset": 1048576, "speed": 0, "type": "stream"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "concluded", "id": "none0"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "null", "id": "none0"}}
{"return": ""}
*** done

1
tests/qemu-iotests/group
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@ -167,6 +167,7 @@
158 rw auto quick
159 rw auto quick
160 rw auto quick
161 rw auto quick
162 auto quick
163 rw auto
165 rw auto quick