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[Qemu-devel] [Bug 1721788] Re: Failed to get shared "write" lock with 'q
From: |
Daniel Berrange |
Subject: |
[Qemu-devel] [Bug 1721788] Re: Failed to get shared "write" lock with 'qemu-img info' |
Date: |
Fri, 06 Oct 2017 14:28:37 -0000 |
The QEMU process that has the disk image open may be doing I/O that
causes qcow2 metadata to be changed. Such changes could confuse the
'qemu-img' process it is was reading the metadata at the same time it
was being changed, causing bad data to be printed or worse. So requiring
a write lock is the 'safe' thing to do for reliability in the worst
case. You can override this by passing '--force-share' arg though.
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https://bugs.launchpad.net/bugs/1721788
Title:
Failed to get shared "write" lock with 'qemu-img info'
Status in QEMU:
New
Bug description:
When running 'qemu-img info test.qcow2' while test.qcow2 is currently
used by a Qemu process, I get the error
qemu-img: Could not open 'test.qcow2': Failed to get shared "write"
lock.
Why does displaying information about a disk image need a write lock for the
file?
Steps to reproduce:
qemu-img create -f qcow2 test.qcow2 10M
qemu-system-x86_64 -nographic -drive file=test.qcow2
qemu-img info test.qcow2
The above was tested with Qemu version 2.10.0
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