Re: [libvirt] [PATCH 1/2] Storage: Suppress metadata refresh for volumes being built.

On Tuesday 05 May 2015 01:52 PM, Ján Tomko wrote: > On Tue, May 05, 2015 at 08:43:21AM +0530, Prerna Saxena wrote: >> Libvirt periodically calls 'stat' on all volumes in a storage pool, >> to update fields such as 'target.allocation'. >> >> The operation doesnt make sense for a volume which is curently being allocated. > From the comments in the storage driver, the point of allowing refresh > for a volume that is currently being allocated is to track the progress > of the allocation. > >> Also, the 'target.allocation' sub-field is taken into account while copying a raw image. >> To suppress any (potential) corruption, libvirt must not attempt to refresh a volume currently being built. > What would be the corruption? > > We do not allow using a volume that is currently building as a > source for cloning the volume - storageVolCreateXMLFrom checks for > origvol->building: > > if (origvol->building) { > virReportError(VIR_ERR_OPERATION_INVALID, > _("volume '%s' is still being allocated."), > origvol->name); > goto cleanup; > } > While running libvirt on PowerPC, I saw an interesting scenario. The 'target.allocation' field seemed to change for a volume getting allocated, and this would lead to incomplete copy. This would happen at random intervals, not deterministically. While looking through the code, I found this to be the other place in code where the same field seemed to change without a lock. Hence the patch. I have sent the second patch which fixes the erring code too : - remain = vol->target.allocation; + remain = inputvol->target.capacity;