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;
Regards,
--
Prerna Saxena
Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India