Re: [libvirt] Question about fsfreeze/fsthaw API

On Thu, Nov 7, 2013 at 11:39 AM, Eric Blake <eblake(a)redhat.com&gt; 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.