Re: [Qemu-devel] [PATCH 9/9] iotests: Add test for COR across nodes

[Max Reitz]

On 2018-04-20 10:43, Stefan Hajnoczi wrote:
> On Mon, Apr 16, 2018 at 06:58:49PM +0200, Max Reitz wrote:
>> diff --git a/tests/qemu-iotests/216 b/tests/qemu-iotests/216
>> new file mode 100755
>> index 00..2f34f94faa
>> --- /dev/null
>> +++ b/tests/qemu-iotests/216
>> @@ -0,0 +1,117 @@
>> +#!/usr/bin/env python
> 
> Welcome to the dark side!

:-)

> Reviewed-by: Stefan Hajnoczi 




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Re: [Qemu-devel] [PATCH 9/9] iotests: Add test for COR across nodes

[Stefan Hajnoczi]

On Mon, Apr 16, 2018 at 06:58:49PM +0200, Max Reitz wrote:
> diff --git a/tests/qemu-iotests/216 b/tests/qemu-iotests/216
> new file mode 100755
> index 00..2f34f94faa
> --- /dev/null
> +++ b/tests/qemu-iotests/216
> @@ -0,0 +1,117 @@
> +#!/usr/bin/env python

Welcome to the dark side!

Reviewed-by: Stefan Hajnoczi 


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[Qemu-devel] [PATCH 9/9] iotests: Add test for COR across nodes

[Max Reitz]

COR across nodes (that is, you have some filter node between the
actually COR target and the node that performs the COR) cannot reliably
work together with the permission system when there is no explicit COR
node that can request the WRITE_UNCHANGED permission for its child.
This is because COR (currently) sneaks its requests by the usual
permission checks, so it can work without a WRITE* permission; but if
there is a filter node in between, that will re-issue the request, which
then passes through the usual check -- and if nobody has requested a
WRITE_UNCHANGED permission, that check will fail.

There is no real direct fix apart from hoping that there is someone who
has requested that permission; in case of just the qemu-io HMP command
(and no guest device), however, that is not the case.  The real real fix
is to implement the copy-on-read flag through an implicitly added COR
node.  Such a node can request the necessary permissions as shown in
this test.

Signed-off-by: Max Reitz 
---
 tests/qemu-iotests/216 | 117 +
 tests/qemu-iotests/216.out |  28 +++
 tests/qemu-iotests/group   |   1 +
 3 files changed, 146 insertions(+)
 create mode 100755 tests/qemu-iotests/216
 create mode 100644 tests/qemu-iotests/216.out

diff --git a/tests/qemu-iotests/216 b/tests/qemu-iotests/216
new file mode 100755
index 00..2f34f94faa
--- /dev/null
+++ b/tests/qemu-iotests/216
@@ -0,0 +1,117 @@
+#!/usr/bin/env python
+#
+# Copy-on-read tests using a COR filter node
+#
+# Copyright (C) 2018 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 .
+#
+# Creator/Owner: Max Reitz 
+#
+# Non-shared storage migration test using NBD server and drive-mirror
+
+import iotests
+from iotests import log, qemu_img_pipe, qemu_io, filter_qemu_io
+
+# Need backing file support
+iotests.verify_image_format(supported_fmts=['qcow2', 'qcow', 'qed', 'vmdk'])
+iotests.verify_platform(['linux'])
+
+log('')
+log('=== Copy-on-read across nodes ===')
+log('')
+
+# The old copy-on-read mechanism without a filter node cannot request
+# WRITE_UNCHANGED permissions for its child.  Therefore it just tries
+# to sneak its write by the usual permission system and holds its
+# fingers crossed.  However, that sneaking does not work so well when
+# there is a filter node in the way: That will receive the write
+# request and re-issue a new one to its child, which this time is a
+# proper write request that will make the permission system cough --
+# unless there is someone at the top (like a guest device) that has
+# requested write permissions.
+#
+# A COR filter node, however, can request the proper permissions for
+# its child and therefore is not hit by this issue.
+
+with iotests.FilePath('base.img') as base_img_path, \
+ iotests.FilePath('top.img') as top_img_path, \
+ iotests.VM() as vm:
+
+log('--- Setting up images ---')
+log('')
+
+qemu_img_pipe('create', '-f', iotests.imgfmt, base_img_path, '64M')
+
+log(filter_qemu_io(qemu_io(base_img_path, '-c', 'write -P 1 0M 1M')))
+
+qemu_img_pipe('create', '-f', iotests.imgfmt, '-b', base_img_path,
+  top_img_path)
+
+log(filter_qemu_io(qemu_io(top_img_path,  '-c', 'write -P 2 1M 1M')))
+
+log('')
+log('--- Doing COR ---')
+log('')
+
+# Compare with e.g. the following:
+#   vm.add_drive_raw('if=none,node-name=node0,copy-on-read=on,driver=raw,' 
\
+#'file.driver=%s,file.file.filename=%s' %
+#   (iotests.imgfmt, top_img_path))
+# (Remove the blockdev-add instead.)
+# ((Not tested here because it hits an assertion in the permission
+#   system.))
+
+vm.launch()
+
+log(vm.qmp('blockdev-add',
+node_name='node0',
+driver='cor',
+file={
+'driver': 'raw',
+'file': {
+'driver': 'cor',
+'file': {
+'driver': 'raw',
+'file': {
+'driver': iotests.imgfmt,
+'file': {
+'driver': 'file',
+'filename': top_img_path
+