[libvirt] [PATCHv3 13/43] snapshot: prevent stranding snapshot data on domain destruction

[Eric Blake]

On 08/24/2011 10:56 AM, Eric Blake wrote:
>>> + VIR_DOMAIN_DESTROY_SNAPSHOTS_FULL = (1<< 2), /* If last use of domain,
>>> + then also remove any
>>> + snapshot data */
>
> But I am starting to be convinced by your assertion that this is
> dangerous - there is no way to cleanly report partial failure with a
> flag like this, which means that in the failure case, it did not add any
> convenience, but made things worse.

[perhaps this email is more for my reference than anything else, since I 
am using the giant thread and all replies in it to track what I still 
need to do before v4 is ready...]

https://www.redhat.com/archives/libvir-list/2011-August/msg01355.html

had more arguments on which flags are most appropriate; the consensus 
there was that snapshot metadata should be automatically deleted on the 
last reference to a domain (such as shutting down a transient domain), 
and that only undefine of a persistent domain should fail because 
snapshot metadata exists (for all other situations, the auto-deletion of 
metadata is sufficient).  Meanwhile, I also need to guarantee that it is 
possible to reload snapshot state from external sources (i.e. allow a 
snapshot redefinition to reinstate metadata).  My holdup for posting a 
v4 of this series is getting all that added, but I will keep my git 
repository up-to-date with the latest state of my series as I keep 
posting stream-of-development patches as replies into this v3 series.

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