[PATCH 2/2] snapshot: enforce REVERT_FORCE on qemu

[Eric Blake <eblake@xxxxxxxxxx>]

Implements the documentation for snapshot revert vs. force.

Part of the patch tightens existing behavior (previously, reverting
to an old snapshot without <domain> was blindly attempted, now it
requires force), while part of it relaxes behavior (previously, it
was not possible to revert an active domain to an ABI-incompatible
active snapshot, now force allows this transition).

* src/qemu/qemu_driver.c (qemuDomainRevertToSnapshot): Check for
risky situations, and allow force to get past them.
---
 src/qemu/qemu_driver.c |   47 +++++++++++++++++++++++++++++++++++++----------
 1 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 5110102..efd60a7 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -9753,7 +9753,8 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
      * 7. paused   -> inactive: EVENT_STOPPED
      * 8. paused   -> running:  EVENT_RESUMED
      * 9. paused   -> paused:   none
-     * Also, several transitions occur even if we fail partway through.
+     * Also, several transitions occur even if we fail partway through,
+     * and use of FORCE can cause multiple transitions.
      */

     qemuDriverLock(driver);
@@ -9789,6 +9790,24 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
                           "yet"));
         goto cleanup;
     }
+    if (!(flags & VIR_DOMAIN_SNAPSHOT_REVERT_FORCE)) {
+        if (!snap->def->dom) {
+            qemuReportError(VIR_ERR_SNAPSHOT_REVERT_RISKY,
+                            _("snapshot lacks domain '%s' rollback details"),
+                            snap->def->name);
+            goto cleanup;
+        }
+        if (virDomainObjIsActive(vm) &&
+            !(snap->def->state == VIR_DOMAIN_RUNNING
+              || snap->def->state == VIR_DOMAIN_PAUSED) &&
+            (flags & (VIR_DOMAIN_SNAPSHOT_REVERT_RUNNING |
+                      VIR_DOMAIN_SNAPSHOT_REVERT_PAUSED))) {
+            qemuReportError(VIR_ERR_SNAPSHOT_REVERT_RISKY,
+                            _("must respawn qemu to start inactive snapshot"));
+            goto cleanup;
+        }
+    }
+

     if (vm->current_snapshot) {
         vm->current_snapshot->def->current = false;
@@ -9818,11 +9837,6 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
         VIR_FREE(xml);
         if (!config)
             goto cleanup;
-    } else {
-        /* XXX Fail if VIR_DOMAIN_REVERT_FORCE is not set, rather than
-         * blindly hoping for the best.  */
-        VIR_WARN("snapshot is lacking rollback information for domain '%s'",
-                 snap->def->name);
     }

     if (qemuDomainObjBeginJobWithDriver(driver, vm, QEMU_JOB_MODIFY) < 0)
@@ -9843,10 +9857,22 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
             /* Transitions 5, 6, 8, 9 */
             /* Check for ABI compatibility.  */
             if (config && !virDomainDefCheckABIStability(vm->def, config)) {
-                /* XXX Add VIR_DOMAIN_REVERT_FORCE to permit killing
-                 * and restarting a new qemu, since loadvm monitor
-                 * command won't work.  */
-                goto endjob;
+                if (!(flags & VIR_DOMAIN_SNAPSHOT_REVERT_FORCE)) {
+                    /* Alter existing error to give correct category. */
+                    virErrorPtr err = virGetLastError();
+                    err->code = VIR_ERR_SNAPSHOT_REVERT_RISKY;
+                    goto endjob;
+                }
+                qemuProcessStop(driver, vm, 0,
+                                VIR_DOMAIN_SHUTOFF_FROM_SNAPSHOT);
+                virDomainAuditStop(vm, "from-snapshot");
+                detail = VIR_DOMAIN_EVENT_STOPPED_FROM_SNAPSHOT;
+                event = virDomainEventNewFromObj(vm,
+                                                 VIR_DOMAIN_EVENT_STOPPED,
+                                                 detail);
+                if (event)
+                    qemuDomainEventQueue(driver, event);
+                goto load;
             }

             priv = vm->privateData;
@@ -9882,6 +9908,7 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
                 virDomainObjAssignDef(vm, config, false);
         } else {
             /* Transitions 2, 3 */
+        load:
             was_stopped = true;
             if (config)
                 virDomainObjAssignDef(vm, config, false);
-- 
1.7.4.4

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