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Re: [libvirt] [PATCHv3 03/43] snapshot: properly revert qemu to offline snapshots



On Wed, Aug 24, 2011 at 09:22:20AM -0600, Eric Blake wrote:
> qemuDomainSnapshotRevertInactive has the same FIXMEs as
> qemuDomainSnapshotCreateInactive, so algorithmic fixes to properly
> handle partial loop iterations should be applied later to both
> functions, but we're not making the situation any worse in
> this patch.
> 
> * src/qemu/qemu_driver.c (qemuDomainRevertToSnapshot): Use
> qemu-img rather than 'qemu -loadvm' to revert to offline snapshot.
> (qemuDomainSnapshotRevertInactive): New helper.
> ---
>  src/qemu/qemu_driver.c |   65 +++++++++++++++++++++++++++++++++++++++++------
>  1 files changed, 56 insertions(+), 9 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 7950aff..1caa870 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -8738,6 +8738,52 @@ cleanup:
>      return xml;
>  }
> 
> +/* The domain is expected to be locked and inactive. */
> +static int
> +qemuDomainSnapshotRevertInactive(virDomainObjPtr vm,
> +                                 virDomainSnapshotObjPtr snap)
> +{
> +    const char *qemuimgarg[] = { NULL, "snapshot", "-a", NULL, NULL, NULL };
> +    int ret = -1;
> +    int i;
> +
> +    qemuimgarg[0] = qemuFindQemuImgBinary();
> +    if (qemuimgarg[0] == NULL) {
> +        /* qemuFindQemuImgBinary set the error */
> +        goto cleanup;
> +    }
> +
> +    qemuimgarg[3] = snap->def->name;
> +
> +    for (i = 0; i < vm->def->ndisks; i++) {
> +        /* FIXME: we also need to handle LVM here */
> +        /* FIXME: if we fail halfway through this loop, we are in an
> +         * inconsistent state.  I'm not quite sure what to do about that
> +         */
> +        if (vm->def->disks[i]->device == VIR_DOMAIN_DISK_DEVICE_DISK) {
> +            if (!vm->def->disks[i]->driverType ||
> +                STRNEQ(vm->def->disks[i]->driverType, "qcow2")) {
> +                qemuReportError(VIR_ERR_OPERATION_INVALID,
> +                                _("Disk device '%s' does not support"
> +                                  " snapshotting"),
> +                                vm->def->disks[i]->info.alias);
> +                goto cleanup;
> +            }
> +
> +            qemuimgarg[4] = vm->def->disks[i]->src;
> +
> +            if (virRun(qemuimgarg, NULL) < 0)
> +                goto cleanup;
> +        }
> +    }
> +
> +    ret = 0;
> +
> +cleanup:
> +    VIR_FREE(qemuimgarg[0]);
> +    return ret;
> +}

I know that virRun is implemented in terms of virCommand, but should
be we aiming to convert virRun uses over to directly use virCommand ?

> @@ -8844,14 +8890,9 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>                                               VIR_DOMAIN_EVENT_STARTED_FROM_SNAPSHOT);
>          }
>      } else {
> -        /* qemu is a little funny with running guests and the restoration
> -         * of snapshots.  If the snapshot was taken online,
> -         * then after a "loadvm" monitor command, the VM is set running
> -         * again.  If the snapshot was taken offline, then after a "loadvm"
> -         * monitor command the VM is left paused.  Unpausing it leads to
> -         * the memory state *before* the loadvm with the disk *after* the
> -         * loadvm, which obviously is bound to corrupt something.
> -         * Therefore we destroy the domain and set it to "off" in this case.
> +        /* Newer qemu -loadvm refuses to revert to the state of a snapshot
> +         * created by qemu-img snapshot -c.  If the domain is running, we
> +         * must take it offline; then do the revert using qemu-img.
>           */
> 
>          if (virDomainObjIsActive(vm)) {
> @@ -8861,6 +8902,12 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>                                               VIR_DOMAIN_EVENT_STOPPED,
>                                               VIR_DOMAIN_EVENT_STOPPED_FROM_SNAPSHOT);
>              if (!vm->persistent) {
> +                /* XXX it should be impossible to create an offline snapshot
> +                 * of a transient domain.  Once we fix 'undefine' to convert
> +                 * a defined domain back to transient, that transition should
> +                 * be rejected if any offline snapshots exist.  For now, we
> +                 * just stop the transient domain and quit, without reverting
> +                 * any disk state.  */
>                  if (qemuDomainObjEndJob(driver, vm) > 0)
>                      virDomainRemoveInactive(&driver->domains, vm);
>                  vm = NULL;
> @@ -8868,7 +8915,7 @@ static int qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>              }
>          }
> 
> -        if (qemuDomainSnapshotSetCurrentActive(vm, driver->snapshotDir) < 0)
> +        if (qemuDomainSnapshotRevertInactive(vm, snap) < 0)
>              goto endjob;
>      }
> 

ACK

Daniel
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