Re: [libvirt] [PATCH v2 06/10] blockcommit: document semantics of committing active layer

On 06/06/14 00:52, Eric Blake wrote: > Now that qemu 2.0 allows commit of the active layer, people are > attempting to use virsh blockcommit and getting into a stuck > state, because libvirt is unprepared to handle the two-phase > commit required by qemu. >

> This patch adds a flag to the libvirt API that a user MUST > supply in order to acknowledge that they will be using two-phase > semantics. It might be possible to have a mode where if the > flag is omitted, we automatically do the case 2 semantics on > the user's behalf; but before that happens, I must do additional > patches to track the fact that we are doing an active commit > in the domain XML. Later patches will add support of the flag, > and once 2-phase semantics are working, we can then decide > whether to relax things to allow an omitted flag to cause an > automatic pivot. >

> + /* XXX Should we auto-pivot when COMMIT_ACTIVE is not specified? */ I think we should do it in the future and possibly document the expected behavior. > + if (!(flags & VIR_DOMAIN_BLOCK_COMMIT_ACTIVE)) { > + virReportError(VIR_ERR_INVALID_ARG, > + _("commit of '%s' active layer requires active flag"), > + disk->dst); > + goto endjob; > + } > } > > if (!topSource->backingStore) { ACK, adding the docs for the auto-pivot commit if you don't specify any flag can be postponed.