[libvirt] Question about fsfreeze/fsthaw API

[Eric Blake]

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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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