Re: [libvirt] [PATCH v3 13/18] snapshot: Add VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST flag
On Mon, Mar 04, 2019 at 09:34:40PM -0600, Eric Blake wrote:
Continue the work of the previous patch in making it possible
to copy the state of a transient domain with snapshots from one
host to another, by allowing the destination to perform bulk
redefines. Note that the destination still has to do separate
calls for creating/defining the domain first, and then redefining
the snapshots (that is, there is intentional asymmetry between
dumping the list in virDomainGetXMLDesc() but redefining it via
virDomainSnapshotCreateXML()), but this is better than the
previous state of having to make multiple REDEFINE calls.
What is the intention behind the assymetry?
It feels odd to request the list by a flag to virDomainGetXMLDesc
(because we're not going to reuse the whole <domain>, just the
<snapshots> sub-element here). Having a counterpart to the API doing the
redefine would only mean two calls (GetXMLDesc, GetSnapshots) instead of
getting every snapshot separately.
Also, virDomainSnapshotCreateXML is designed for a single snapshot,
using a flag to turn it into a different API ('virDomainSnapshotsCreateXML'?
'virDomainSnapshotsRedefine'?) leads to strangeness like returning
a single snapshot while making no guarantees on which one it is
or a repetition of this pattern:
if (flags & REDEFINE_LIST) {
/* ... */
goto cleanup; /* <- no fallthrough here */
}
Jano
The
bulk flag requires no pre-existing snapshot metadata (as that
makes life much easier if there is a failure encountered partway
through the list processing - simply remove all other snapshot
metadatas), and makes no guarantees on which snapshot (when there
are multiple) will actually be returned.
Actual driver implementations will be in later patches.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
Reviewed-by: John Ferlan <jferlan(a)redhat.com>
---
include/libvirt/libvirt-domain-snapshot.h | 3 +++
src/libvirt-domain-snapshot.c | 23 +++++++++++++++++++----
2 files changed, 22 insertions(+), 4 deletions(-)
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