[PATCH 1/2] qemu: introduce locking option for disk source of qemu
Daniel P. Berrangé
berrange at redhat.com
Mon Jan 25 09:35:42 UTC 2021
On Sat, Jan 23, 2021 at 11:12:15AM +0100, Peter Krempa wrote:
> On Fri, Jan 22, 2021 at 21:32:05 -0500, Masayoshi Mizuma wrote:
> > From: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> > Introduce locking option for disk source of qemu.
> > It may be useful to avoid file lock issues.
> Lock issues usually mean that you are doing something wrong.
> > locking option supports three switches; 'auto', 'on' and 'off'.
> > The default behaivor will work if locking option isn't set.
> > Example of the usage:
> > <disk type='file' device='disk'>
> > <driver name='qemu' type='qcow2' cache='none'/>
> > <source file='/tmp/QEMUGuest1.img' locking='off'/>
> > <target dev='hda' bus='ide'/>
> > <address type='drive' controller='0' bus='0' target='0' unit='0'/>
> > </disk>
> > Signed-off-by: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> > ---
> > docs/schemas/domaincommon.rng | 9 +++++++++
> > src/conf/domain_conf.c | 8 ++++++++
> > src/conf/storage_source_conf.c | 9 +++++++++
> > src/conf/storage_source_conf.h | 14 ++++++++++++++
> > src/libvirt_private.syms | 1 +
> > src/qemu/qemu_block.c | 5 +++++
> > 6 files changed, 46 insertions(+)
> Few quick notes:
> - I'm not entirely persuaded that we should at this at all
> - qemu locking works to prevent user mistakes
> - you really need to know what to expect if you use images which are
> used by multiple VMs
> - you really need to add some form of justification, the current one
> definitely is insufficient and thus I'm inclined to NACKing the
> concept of enabling setting of the locks completely
I agree - we should be providing higher level conceptual logic that
indirectly maps into the different locking states.
For example we have <readonly/> and <shareable/> elements that
influence the type of locks held. A flag to unconditionally
disable locking entirely feels like it is just hacking around
some undefined problem that should be fixed in a better way.
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