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Re: [libvirt] [PATCH 2/4] snapshot: track qemu snapshot relations



On Fri, Oct 07, 2011 at 06:05:55PM -0600, Eric Blake wrote:
> Maintain the parent/child relationships of all qemu snapshots.
> 
> * src/qemu/qemu_driver.c (qemuDomainSnapshotLoad): Populate
> relationships after loading.
> (qemuDomainSnapshotCreateXML): Set relations on creation; tweak
> redefinition to reuse existing object.
> (qemuDomainSnapshotReparentChildren, qemuDomainSnapshotDelete):
> Clear relations on delete.
> ---
>  src/qemu/qemu_driver.c |   72 ++++++++++++++++++++++++++++++++++++++---------
>  1 files changed, 58 insertions(+), 14 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 5db67b8..501a3fc 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -376,6 +376,10 @@ static void qemuDomainSnapshotLoad(void *payload,
>          vm->current_snapshot = NULL;
>      }
> 
> +    if (virDomainSnapshotUpdateRelations(&vm->snapshots) < 0)
> +        VIR_ERROR(_("Snapshots have inconsistent relations for domain %s"),
> +                  vm->def->name);
> +

 Hum, so we error out but continue with possibly inconsistent metadata,
isn't that risky ? What would be the cost or failing the load here and
consequences of lack of metadata ?

>      /* FIXME: qemu keeps internal track of snapshots.  We can get access
>       * to this info via the "info snapshots" monitor command for running
>       * domains, or via "qemu-img snapshot -l" for shutoff domains.  It would
> @@ -9148,6 +9152,7 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
>      virDomainSnapshotDefPtr def = NULL;
>      bool update_current = true;
>      unsigned int parse_flags = 0;
> +    virDomainSnapshotObjPtr other = NULL;
> 
>      virCheckFlags(VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE |
>                    VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT |
> @@ -9190,8 +9195,6 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
>          goto cleanup;
> 
>      if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE) {
> -        virDomainSnapshotObjPtr other = NULL;
> -
>          /* Prevent circular chains */
>          if (def->parent) {
>              if (STREQ(def->name, def->parent)) {
> @@ -9267,7 +9270,12 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
>                  update_current = true;
>                  vm->current_snapshot = NULL;
>              }
> -            virDomainSnapshotObjListRemove(&vm->snapshots, other);
> +            /* Drop and rebuild the parent relationship, but keep all
> +             * child relations by reusing snap.  */
> +            virDomainSnapshotDropParent(&vm->snapshots, other);
> +            virDomainSnapshotDefFree(other->def);
> +            other->def = NULL;
> +            snap = other;
>          }
>          if (def->state == VIR_DOMAIN_DISK_SNAPSHOT && def->dom) {
>              if (virDomainSnapshotAlignDisks(def,
> @@ -9309,7 +9317,9 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
>          }
>      }
> 
> -    if (!(snap = virDomainSnapshotAssignDef(&vm->snapshots, def)))
> +    if (snap)
> +        snap->def = def;
> +    else if (!(snap = virDomainSnapshotAssignDef(&vm->snapshots, def)))
>          goto cleanup;
>      def = NULL;
> 
> @@ -9366,11 +9376,25 @@ cleanup:
>      if (vm) {
>          if (snapshot && !(flags & VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA)) {
>              if (qemuDomainSnapshotWriteMetadata(vm, snap,
> -                                                driver->snapshotDir) < 0)
> +                                                driver->snapshotDir) < 0) {
>                  VIR_WARN("unable to save metadata for snapshot %s",
>                           snap->def->name);
> -            else if (update_current)
> -                vm->current_snapshot = snap;
> +            } else {
> +                if (update_current)
> +                    vm->current_snapshot = snap;
> +                if (snap->def->parent) {
> +                    other = virDomainSnapshotFindByName(&vm->snapshots,
> +                                                        snap->def->parent);
> +                    snap->parent = other;
> +                    other->nchildren++;
> +                    snap->sibling = other->first_child;
> +                    other->first_child = snap;
> +                } else {
> +                    vm->snapshots.nroots++;
> +                    snap->sibling = vm->snapshots.first_root;
> +                    vm->snapshots.first_root = snap;
> +                }
> +            }
>          } else if (snap) {
>              virDomainSnapshotObjListRemove(&vm->snapshots, snap);
>          }
> @@ -10062,9 +10086,10 @@ cleanup:
> 
>  struct snap_reparent {
>      struct qemud_driver *driver;
> -    const char *parent;
> +    virDomainSnapshotObjPtr parent;
>      virDomainObjPtr vm;
>      int err;
> +    virDomainSnapshotObjPtr last;
>  };
> 
>  static void
> @@ -10080,9 +10105,10 @@ qemuDomainSnapshotReparentChildren(void *payload,
>      }
> 
>      VIR_FREE(snap->def->parent);
> +    snap->parent = rep->parent;
> 
> -    if (rep->parent != NULL) {
> -        snap->def->parent = strdup(rep->parent);
> +    if (rep->parent) {
> +        snap->def->parent = strdup(rep->parent->def->name);
> 
>          if (snap->def->parent == NULL) {
>              virReportOOMError();
> @@ -10091,6 +10117,9 @@ qemuDomainSnapshotReparentChildren(void *payload,
>          }
>      }
> 
> +    if (!snap->sibling)
> +        rep->last = snap;
> +
>      rep->err = qemuDomainSnapshotWriteMetadata(rep->vm, snap,
>                                                 rep->driver->snapshotDir);
>  }
> @@ -10175,22 +10204,37 @@ static int qemuDomainSnapshotDelete(virDomainSnapshotPtr snapshot,
>              }
>              vm->current_snapshot = snap;
>          }
> -    } else {
> +    } else if (snap->nchildren) {
>          rep.driver = driver;
> -        rep.parent = snap->def->parent;
> +        rep.parent = snap->parent;
>          rep.vm = vm;
>          rep.err = 0;
> +        rep.last = NULL;
>          virDomainSnapshotForEachChild(&vm->snapshots, snap,
>                                        qemuDomainSnapshotReparentChildren,
>                                        &rep);
>          if (rep.err < 0)
>              goto endjob;
> +        /* Can't modify siblings during ForEachChild, so do it now.  */
> +        if (snap->parent) {
> +            snap->parent->nchildren += snap->nchildren;
> +            rep.last->sibling = snap->parent->first_child;
> +            snap->parent->first_child = snap->first_child;
> +        } else {
> +            vm->snapshots.nroots += snap->nchildren;
> +            rep.last->sibling = vm->snapshots.first_root;
> +            vm->snapshots.first_root = snap->first_child;
> +        }
>      }
> 
> -    if (flags & VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY)
> +    if (flags & VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY) {
> +        snap->nchildren = 0;
> +        snap->first_child = NULL;
>          ret = 0;
> -    else
> +    } else {
> +        virDomainSnapshotDropParent(&vm->snapshots, snap);
>          ret = qemuDomainSnapshotDiscard(driver, vm, snap, true, metadata_only);
> +    }
> 
>  endjob:
>      if (qemuDomainObjEndJob(driver, vm) == 0)

  Okay, the main problem is making sure we keep the metadata on all
  operations that are needed, Load/Create/Delete and Reparent sounds
  right,

  ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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