On 3/20/19 4:28 PM, John Ferlan wrote:
>
>
> On 3/20/19 1:40 AM, Eric Blake wrote:
>> Rather than allowing a leaky abstraction where multiple drivers have
>> to open-code operations that update the relations in a
>> virDomainSnapshotObjList, it is better to add accessor functions so
>> that updates to relations are maintained closer to the internals. The
>> goal here is to avoid access to, nchildren, first_child, or sibling
>> outside of the lowest level functions, making it easier to refactor
>> later on. While many of the conversions are fairly straightforward,
>> the MoveChildren refactoring can be a bit interesting to follow.
>
> Understatement ;-) Some black magic occurs
>
> The qemuDomainSnapshotReparentChildren "snap->parent = rep->parent" gets
> replaced by the new for loop... Tough to see without watching really
> closely.
>
>> +/* Take all children of @from and convert them into children of @to. */
>> +void
>> +virDomainSnapshotMoveChildren(virDomainSnapshotObjPtr from,
>> + virDomainSnapshotObjPtr to)
>> +{
>> + virDomainSnapshotObjPtr child;
>> + virDomainSnapshotObjPtr last;
>> +
>> + for (child = from->first_child; child; child = child->sibling) {
>> + child->parent = to;
>> + if (!child->sibling)
>> + last = child;
>> + }
>> + to->nchildren += from->nchildren;
>> + last->sibling = to->first_child;
>
> Silly Coverity compiler gets quite confused thinking that @last couldn't
> be set while not considering the above loop couldn't end without it
> unless of course from->first_child == NULL I suppose, which would be a
> different issue. Still if before the for loop we check "if
> (!from->first_child) return;", then coverity is happy.
Good find from Coverity. If there are no children to move, I do need the
early exit, so I'll squash that in.
>
>> + to->first_child = from->first_child;
>> + from->nchildren = 0;
>> + from->first_child = NULL;
>
> Or virDomainSnapshotDropChildren... Still makes sense, albeit new. Seems
> to make VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY processing unnecessary.
> It's not a problem but perhaps worthy of a mention.
I'll call out more details in the commit message.
>> - if (snapshots->metaroot.nchildren || snapshots->current) {
>> + if (virDomainSnapshotObjListSize(snapshots)) {
>
> The only way the call could return < 0 from virHashSize is if @snapshots
> == NULL... Just noting it - no problem.
Yeah, we don't want to continue with either a -1 error (which shouldn't
happen in practice) or a > 0 result (more likely); but adding '!= 0'
does appear to make it clearer that I thought about both directions.
>
>> virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>> _("bulk define of snapshots only possible with "
>> "no existing snapshot"));
>
> Reviewed-by: John Ferlan <jferlan@xxxxxxxxxx>
>
> John
>
> BTW: There could have been 3 patches out of this, but I'm fine with 1.
I ended up splitting into two - everything else is simple, and then
MoveChildren in isolation.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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