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Re: [libvirt] [PATCHv4 34/51] snapshot: store qemu domain details in xml

On 09/01/2011 10:25 PM, Eric Blake wrote:
When reverting to a snapshot, the inactive domain configuration
has to be rolled back to what it was at the time of the snapshot.
Additionally, if the VM is active and the snapshot was active,
this now adds a failure if the two configurations are ABI
incompatible, rather than risking qemu confusion.

A future patch will add a VIR_DOMAIN_SNAPSHOT_FORCE flag, which
will be required for two risky code paths - reverting to an
older snapshot that lacked full domain information, and reverting
from running to a live snapshot that requires starting a new qemu
process.  Any reverting that stops a running vm is also a form
of data loss (discarding the current running state to go back in
time), but as that is what reversion usually implies, it is
probably not worth requiring a force flag.

* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateXML): Copy out
(qemuDomainRevertToSnapshot): Perform ABI compatibility checks.
  src/qemu/qemu_driver.c |   77 +++++++++++++++++++++++++++++++++++++++--------
  1 files changed, 64 insertions(+), 13 deletions(-)

I'm squashing in these additional safety checks, now that domain snapshot redefine is also a place where ABI compatibility matters.

diff --git i/src/qemu/qemu_driver.c w/src/qemu/qemu_driver.c
index ea11d0b..7028d72 100644
--- i/src/qemu/qemu_driver.c
+++ w/src/qemu/qemu_driver.c
@@ -8826,6 +8826,13 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,

         /* Check that any replacement is compatible */
+        if (def->dom &&
+            memcmp(def->dom->uuid, domain->uuid, VIR_UUID_BUFLEN)) {
+            qemuReportError(VIR_ERR_INVALID_ARG,
+ _("definition for snapshot %s must use uuid %s"),
+                            def->name, uuidstr);
+            goto cleanup;
+        }
         other = virDomainSnapshotFindByName(&vm->snapshots, def->name);
         if (other) {
             if ((other->def->state == VIR_DOMAIN_RUNNING ||
@@ -8838,7 +8845,17 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
                 goto cleanup;
-            /* XXX Ensure ABI compatibility before replacing anything.  */
+            if (other->def->dom) {
+                if (def->dom) {
+                    if (!virDomainDefCheckABIStability(other->def->dom,
+                                                       def->dom))
+                        goto cleanup;
+                } else {
+                    /* Transfer the domain def */
+                    def->dom = other->def->dom;
+                    other->def->dom = NULL;
+                }
+            }
             if (other == vm->current_snapshot) {
                 update_current = true;
                 vm->current_snapshot = NULL;

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

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