[libvirt] [RFC PATCH] snapshot: better virsh handling of missing current, parent

[Eric Blake]

On 10/04/2011 12:54 PM, Laine Stump wrote:
> On 09/30/2011 12:19 PM, Eric Blake wrote:
>> Previously, virsh 'snapshot-parent' and 'snapshot-current' were
>> completely silent in the case where the code conclusively proved
>> there was no parent or current snapshot, but differed in exit
>> status; this silence caused some confusion on whether the commands
>> worked. Furthermore, commit d1be48f introduced a regression where
>> snapshot-parent would leak output about an unknown function, but
>> only on the first attempt, when talking to an older server that
>> lacks virDomainSnapshotGetParent. This changes things to consistenly
>> report an error message and exit with status 1 when no snapshot
>> exists, and to avoid leaking unknown function warnings when using
>> fallbacks.
>>
>> Preferences? (I guess mine is approach 1, by evidence of this patch).
>
>
> The code all looks fine, so ACK to that. Not being very familiar with
> the snapshot stuff, I can't say that I have an valid opinion on whether
> it's better to log an error or exit silently when there is no parent. I
> guess I would defer to your opinion, since you're the person who's spent
> the most time dealing with snapshots lately :-)

I went ahead and pushed this as-is, on the basis that a common usage 
pattern, virsh snapshot-revert dom $(virsh snapshot-current --name), 
will do the right thing when there is no stdout, whether or not stderr 
was supplied, but having stderr available can help understand the 
situation when using the command in isolation.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org