Bug 1226996

Summary:	qcow2: Fix minimum L2 cache size
Product:	Red Hat Enterprise Linux 7	Reporter:	Kevin Wolf <kwolf>
Component:	qemu-kvm-rhev	Assignee:	Hanna Czenczek <hreitz>
Status:	CLOSED ERRATA	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	7.2	CC:	huding, juzhang, virt-maint, xfu, xwei
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	qemu-kvm-rhev-2.3.0-3.el7	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2015-12-04 16:43:32 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Kevin Wolf 2015-06-01 15:37:36 UTC

The minimum L2 table cache size for qcow2 is incorrectly defined as 1. It needs
to be at least 2 for COW operations on L2 tables to work (this happens with
internal snapshots); otherwise an abort() is triggered.

The problem can be reproduced as follows:

$ qemu-img create -f qcow2 /tmp/test.qcow2 -o cluster_size=1M 64M
Formatting '/tmp/test.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1048576 lazy_refcounts=off refcount_bits=16
$ qemu-io -c 'write 0 1M' /tmp/test.qcow2
wrote 1048576/1048576 bytes at offset 0
1 MiB, 1 ops; 0.0836 sec (11.952 MiB/sec and 11.9524 ops/sec)
$ qemu-img snapshot -c test /tmp/test.qcow2
$ qemu-io -c 'write 0 1M' /tmp/test.qcow2
Aborted (core dumped)

Comment 1 Miroslav Rezanina 2015-06-19 11:09:13 UTC

Fix included in qemu-kvm-rhev-2.3.0-3.el7

Comment 3 Xiaoqing Wei 2015-07-03 05:42:49 UTC

on qemu-kvm-rhev-2.3.0-7.el7
[root@dhcp-11-50 ~]# qemu-img create -f qcow2 /tmp/test.qcow2 -o cluster_size=1M 64M
Formatting '/tmp/test.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1048576 lazy_refcounts=off refcount_bits=16
[root@dhcp-11-50 ~]# qemu-io -c 'write 0 1M' /tmp/test.qcow2
wrote 1048576/1048576 bytes at offset 0
1 MiB, 1 ops; 0.1905 sec (5.248 MiB/sec and 5.2480 ops/sec)
[root@dhcp-11-50 ~]# qemu-img snapshot -c test /tmp/test.qcow2
[root@dhcp-11-50 ~]# qemu-io -c 'write 0 1M' /tmp/test.qcow2
wrote 1048576/1048576 bytes at offset 0
1 MiB, 1 ops; 0.2569 sec (3.892 MiB/sec and 3.8915 ops/sec)


 downgrade to qemu-kvm-rhev-2.3.0-2.el7

[root@dhcp-11-50 ~]# qemu-img create -f qcow2 /tmp/test.qcow2 -o cluster_size=1M 64M
Formatting '/tmp/test.qcow2', fmt=qcow2 size=67108864 encryption=off cluster_size=1048576 lazy_refcounts=off refcount_bits=16
[root@dhcp-11-50 ~]# qemu-io -c 'write 0 1M' /tmp/test.qcow2
wrote 1048576/1048576 bytes at offset 0
1 MiB, 1 ops; 0.3554 sec (2.813 MiB/sec and 2.8131 ops/sec)
[root@dhcp-11-50 ~]# qemu-img snapshot -c test /tmp/test.qcow2
[root@dhcp-11-50 ~]# qemu-io -c 'write 0 1M' /tmp/test.qcow2
Aborted (core dumped)



move to VERIFIED

Comment 5 errata-xmlrpc 2015-12-04 16:43:32 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2546.html