Eric Blake d16e5b15ed snapshots: Add flag to guarantee topological sort ... When using virDomainSnapshotCreateXML with the REDEFINE flag on multiple snapshot metadata XML descriptions, we require that a child cannot be redefined before its parent. Since libvirt already tracks a DAG, it is more convenient if we can ensure that virDomainListAllSnapshots() and friends have a way to return data in an order that we can directly reuse, rather than having to post-process the data ourselves to reconstruct the DAG. Add VIR_DOMAIN_SNAPSHOT_LIST_TOPOLOGICAL as our new guarantee (well, a guarantee at the time of the API call conclusion; there's always a possible TOCTTOU race where someone redefining snapshots in between the API results and the client actually using the list might render the list out-of-date). Four listing APIs are directly benefitted by the new flag; additionally, since we document that the older racy ListNames interfaces should be sized by using the same flags on their Num counterparts, the Num interfaces must document when they accept (and ignore) the flag. We could have supported the new flag just for the ListAll APIs (to discourage people from using the older racy Num/ListNames APIs), but it feels weird to special-case this flag value as being applicable to only a subset of the API while all other List-related flags are trivially applicable to all 6. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>		2019-03-12 20:38:53 -05:00
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libvirt	snapshots: Add flag to guarantee topological sort	2019-03-12 20:38:53 -05:00