[libvirt] [PATCH v3 13/18] snapshot: Add VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST flag

[Eric Blake]

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.  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 at redhat.com>
Reviewed-by: John Ferlan <jferlan at redhat.com>
---
 include/libvirt/libvirt-domain-snapshot.h |  3 +++
 src/libvirt-domain-snapshot.c             | 23 +++++++++++++++++++----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/libvirt/libvirt-domain-snapshot.h b/include/libvirt/libvirt-domain-snapshot.h
index d9b689abbd..7e6eff6a9a 100644
--- a/include/libvirt/libvirt-domain-snapshot.h
+++ b/include/libvirt/libvirt-domain-snapshot.h
@@ -71,6 +71,9 @@ typedef enum {
     VIR_DOMAIN_SNAPSHOT_CREATE_LIVE        = (1 << 8), /* create the snapshot
                                                           while the guest is
                                                           running */
+    VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST = (1 << 9), /* parse multiple
+                                                            snapshots in one
+                                                            API call */
 } virDomainSnapshotCreateFlags;

 /* Take a snapshot of the current VM state */
diff --git a/src/libvirt-domain-snapshot.c b/src/libvirt-domain-snapshot.c
index a647a500d6..ab94d29574 100644
--- a/src/libvirt-domain-snapshot.c
+++ b/src/libvirt-domain-snapshot.c
@@ -1,7 +1,7 @@
 /*
  * libvirt-domain-snapshot.c: entry points for virDomainSnapshotPtr APIs
  *
- * Copyright (C) 2006-2014 Red Hat, Inc.
+ * Copyright (C) 2006-2019 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -102,7 +102,7 @@ virDomainSnapshotGetConnect(virDomainSnapshotPtr snapshot)
  * @flags: bitwise-OR of virDomainSnapshotCreateFlags
  *
  * Creates a new snapshot of a domain based on the snapshot xml
- * contained in xmlDesc.
+ * contained in xmlDesc, with a top-level <domainsnapshot> element.
  *
  * If @flags is 0, the domain can be active, in which case the
  * snapshot will be a full system snapshot (capturing both disk state,
@@ -132,8 +132,17 @@ virDomainSnapshotGetConnect(virDomainSnapshotPtr snapshot)
  * guest-visible layout.  When redefining a snapshot name that does
  * not exist, the hypervisor may validate that reverting to the
  * snapshot appears to be possible (for example, disk images have
- * snapshot contents by the requested name).  Not all hypervisors
- * support these flags.
+ * snapshot contents by the requested name).  Alternatively, if @flags
+ * includes VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST (which requires
+ * VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE and is incompatible with
+ * VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT), and the domain has no existing
+ * snapshot metadata, then @xmlDesc is parsed as a top-level
+ * <snapshots> element with an optional current='name' attribute, and
+ * containing one or more <domainsnapshot> children (as produced by
+ * virDomainGetXMLDesc() with the flag VIR_DOMAIN_XML_SNAPSHOTS), to
+ * do a bulk redefine of all snapshots at once (it is unspecified
+ * which of the redefined snapshots will be used as the return value
+ * on success).  Not all hypervisors support these flags.
  *
  * If @flags includes VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA, then the
  * domain's disk images are modified according to @xmlDesc, but then
@@ -219,6 +228,9 @@ virDomainSnapshotCreateXML(virDomainPtr domain,
     VIR_REQUIRE_FLAG_GOTO(VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT,
                           VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE,
                           error);
+    VIR_REQUIRE_FLAG_GOTO(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST,
+                          VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE,
+                          error);

     VIR_EXCLUSIVE_FLAGS_GOTO(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE,
                              VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA,
@@ -226,6 +238,9 @@ virDomainSnapshotCreateXML(virDomainPtr domain,
     VIR_EXCLUSIVE_FLAGS_GOTO(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE,
                              VIR_DOMAIN_SNAPSHOT_CREATE_HALT,
                              error);
+    VIR_EXCLUSIVE_FLAGS_GOTO(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE_LIST,
+                             VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT,
+                             error);

     if (conn->driver->domainSnapshotCreateXML) {
         virDomainSnapshotPtr ret;
-- 
2.20.1