[libvirt] Question about fsfreeze/fsthaw API

Doug Goldstein cardoe at gentoo.org
Thu Nov 7 19:05:42 UTC 2013


On Thu, Nov 7, 2013 at 11:39 AM, Eric Blake <eblake at redhat.com> wrote:
> On 11/06/2013 05:31 PM, Tomoki Sekiyama wrote:
>> Hi all,
>>
>> Is there any plans to add APIs to execute fsfreeze/fsthaw in qemu guests?
>> (something like virDomainFSFreeze(domain,timeout,flags) and
>>                 virDomainFSThaw(domain,timeout,flags))
>
> I'm wondering if it might be better to have a single command with a
> callback argument, something like:
>
> virDomainQuiese(domain, timeout, callback, opaque, flags)
>
> which calls callback(domain, opaque) at the right point in time.  I'm
> just a bit worried that since the freeze/thaw sequence is already
> handled as a pair by the QUIESCE flag of snapshot creation that exposing
> it as two non-atomic APIs may lead to inconsistent states that we'd have
> a hard time tracking which commands are allowed in which state.  With
> only a single command and a callback, we have guaranteed semantics that
> all other API are locked out by our normal job mechanism, and that we
> can pair the freeze/thaw under the hood just as we do in snapshots.

I think this is a much better approach. We could arguably refactor the
snapshot code to use this as well.

-- 
Doug Goldstein




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