[libvirt] [PATCHv3 29/43] snapshot: allow halting after snapshot

[Eric Blake]

Since a snapshot is fully recoverable, it is useful to have a
snapshot as a means of hibernating a guest, then reverting to
the snapshot to wake the guest up.  This mode of usage is
similar to 'virsh save/virsh restore', except that virsh
save uses an external file while virsh snapshot keeps the
vm state internal to a qcow2 file.

In the usage pattern of snapshot/revert for hibernating a guest,
there is no need to keep the guest running between the two points
in time, especially since that would generate runtime state that
would just be discarded.  Add a flag to make it possible to
stop the domain after the snapshot has completed.

* include/libvirt/libvirt.h.in (VIR_DOMAIN_SNAPSHOT_CREATE_HALT):
New flag.
* src/libvirt.c (virDomainSnapshotCreateXML): Document it.
* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateXML)
(qemuDomainSnapshotCreateActive): Implement it.
---
 include/libvirt/libvirt.h.in |    5 +++++
 src/libvirt.c                |   15 ++++++++++++++-
 src/qemu/qemu_driver.c       |   33 +++++++++++++++++++++++++++++----
 3 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
index 49fe6b3..e07dc20 100644
--- a/include/libvirt/libvirt.h.in
+++ b/include/libvirt/libvirt.h.in
@@ -2559,6 +2559,11 @@ typedef struct _virDomainSnapshot virDomainSnapshot;
  */
 typedef virDomainSnapshot *virDomainSnapshotPtr;

+typedef enum {
+    VIR_DOMAIN_SNAPSHOT_CREATE_HALT = (1 << 0), /* Stop running guest after
+                                                   snapshot is complete */
+} virDomainSnapshotCreateFlags;
+
 /* Take a snapshot of the current VM state */
 virDomainSnapshotPtr virDomainSnapshotCreateXML(virDomainPtr domain,
                                                 const char *xmlDesc,
diff --git a/src/libvirt.c b/src/libvirt.c
index 2c84e7e..ffd27bc 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -15464,11 +15464,24 @@ error:
  * virDomainSnapshotCreateXML:
  * @domain: a domain object
  * @xmlDesc: string containing an XML description of the domain
- * @flags: unused flag parameters; callers should pass 0
+ * @flags: bitwise-OR of virDomainSnapshotCreateFlags
  *
  * Creates a new snapshot of a domain based on the snapshot xml
  * contained in xmlDesc.
  *
+ * If @flags is 0, the domain can be active, in which case the
+ * snapshot will be a system checkpoint (both disk state and runtime
+ * VM state such as RAM contents), where reverting to the snapshot is
+ * the same as resuming from hibernation (TCP connections may have
+ * timed out, but everything else picks up where it left off); or
+ * the domain can be inactive, in which case the snapshot includes
+ * just the disk state prior to booting.
+ *
+ * If @flags includes VIR_DOMAIN_SNAPSHOT_CREATE_HALT, then the domain
+ * will be inactive after the snapshot completes, regardless of whether
+ * it was active before; otherwise, a running domain will still be
+ * running after the snapshot.  This flag is invalid on transient domains.
+ *
  * Returns an (opaque) virDomainSnapshotPtr on success, NULL on failure.
  */
 virDomainSnapshotPtr
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index a8cd9f8..ae63a02 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -8608,7 +8608,8 @@ static int
 qemuDomainSnapshotCreateActive(virConnectPtr conn,
                                struct qemud_driver *driver,
                                virDomainObjPtr *vmptr,
-                               virDomainSnapshotObjPtr snap)
+                               virDomainSnapshotObjPtr snap,
+                               unsigned int flags)
 {
     virDomainObjPtr vm = *vmptr;
     qemuDomainObjPrivatePtr priv = vm->privateData;
@@ -8638,6 +8639,24 @@ qemuDomainSnapshotCreateActive(virConnectPtr conn,
     qemuDomainObjEnterMonitorWithDriver(driver, vm);
     ret = qemuMonitorCreateSnapshot(priv->mon, snap->def->name);
     qemuDomainObjExitMonitorWithDriver(driver, vm);
+    if (ret < 0)
+        goto cleanup;
+
+    if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_HALT) {
+        virDomainEventPtr event;
+
+        event = virDomainEventNewFromObj(vm, VIR_DOMAIN_EVENT_STOPPED,
+                                         VIR_DOMAIN_EVENT_STOPPED_FROM_SNAPSHOT);
+        qemuProcessStop(driver, vm, 0, VIR_DOMAIN_SHUTOFF_FROM_SNAPSHOT);
+        virDomainAuditStop(vm, "from-snapshot");
+        /* We already filtered the _HALT flag for persistent domains
+         * only, so this end job never drops the last reference.  */
+        ignore_value(qemuDomainObjEndJob(driver, vm));
+        resume = false;
+        vm = NULL;
+        if (event)
+            qemuDomainEventQueue(driver, event);
+    }

 cleanup:
     if (resume && virDomainObjIsActive(vm) &&
@@ -8649,7 +8668,7 @@ cleanup:
                         _("resuming after snapshot failed"));
     }

-    if (qemuDomainObjEndJob(driver, vm) == 0) {
+    if (vm && qemuDomainObjEndJob(driver, vm) == 0) {
         /* Only possible if a transient vm quit while our locks were down,
          * in which case we don't want to save snapshot metadata.  */
         *vmptr = NULL;
@@ -8672,7 +8691,7 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
     char uuidstr[VIR_UUID_STRING_BUFLEN];
     virDomainSnapshotDefPtr def = NULL;

-    virCheckFlags(0, NULL);
+    virCheckFlags(VIR_DOMAIN_SNAPSHOT_CREATE_HALT, NULL);

     qemuDriverLock(driver);
     virUUIDFormat(domain->uuid, uuidstr);
@@ -8683,6 +8702,12 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
         goto cleanup;
     }

+    if (!vm->persistent && (flags & VIR_DOMAIN_SNAPSHOT_CREATE_HALT)) {
+        qemuReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                        _("cannot halt after transient domain snapshot"));
+        goto cleanup;
+    }
+
     if (!(def = virDomainSnapshotDefParseString(xmlDesc, 1, NULL, 0, 0)))
         goto cleanup;

@@ -8730,7 +8755,7 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
             goto cleanup;
     } else {
         if (qemuDomainSnapshotCreateActive(domain->conn, driver,
-                                           &vm, snap) < 0)
+                                           &vm, snap, flags) < 0)
             goto cleanup;
     }

-- 
1.7.4.4