Commit 0065c455 authored by Alberto Garcia's avatar Alberto Garcia Committed by Kevin Wolf
Browse files

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: default avatarAlberto Garcia <berto@igalia.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent a237dea3

block.c

+21 −0
Original line number Diff line number Diff line
@@ -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);

    }

tests/qemu-iotests/161

0 → 100755
+104 −0
Original line number Diff line number Diff line 
#!/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

tests/qemu-iotests/161.out

0 → 100644
+23 −0
Original line number Diff line number Diff line 
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

tests/qemu-iotests/group

+1 −0
Original line number Diff line number Diff line
@@ -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