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Re: [libvirt] [PATCHv2 03/13] snapshot: use metaroot node to simplify management



On 06/15/2012 10:21 AM, Eric Blake wrote:

> 
>>> +    flags ^= VIR_DOMAIN_SNAPSHOT_LIST_ROOTS;
>>
>> I'm not quite sure what's the meaning of this statement. It efectively
>> negates the VIR_DOMAIN_SNAPSHOT_LIST_ROOTS flag, but the original code
>> filtered it out.
> 
> ^= toggles, not clears.  Due to (in hind-sight, a rather poor) choice on
> my part in 0.9.7 when adding the ability to list children, we are stuck
> with the following two bits with opposite meanings:

> 
>> ACK if the flag masking issue gets cleared. The metaroot approach is
>> nice and consistent.

It turns out that 3-5 are also independent of Peter's series, so I will
push those shortly as well.

> 
> Then, assuming my explanation is okay, I will resolve this by adding
> more comments to the code.

Here's what I'm squashing in.

diff --git i/src/conf/domain_conf.c w/src/conf/domain_conf.c
index c7437af..43872d1 100644
--- i/src/conf/domain_conf.c
+++ w/src/conf/domain_conf.c
@@ -14272,8 +14272,9 @@ static void
virDomainSnapshotObjListCopyNames(void *payload,

     if (data->oom)
         return;
-    /* LIST_ROOTS/LIST_DESCENDANTS was handled by caller,
-     * LIST_METADATA is a no-op if we get this far.  */
+    /* LIST_ROOTS/LIST_DESCENDANTS was handled by the choice of
+     * iteration made in the caller, and LIST_METADATA is a no-op if
+     * we get this far.  */
     if ((data->flags & VIR_DOMAIN_SNAPSHOT_LIST_LEAVES) && obj->nchildren)
         return;

@@ -14289,6 +14290,9 @@ int
virDomainSnapshotObjListGetNames(virDomainSnapshotObjListPtr snapshots,
                                      char **const names, int maxnames,
                                      unsigned int flags)
 {
+    /* LIST_ROOTS and LIST_DESCENDANTS have the same bit value, but
+     * opposite semantics.  Toggle here to get the correct traversal
+     * on the metaroot.  */
     flags ^= VIR_DOMAIN_SNAPSHOT_LIST_ROOTS;
     return virDomainSnapshotObjListGetNamesFrom(&snapshots->metaroot,
names,
                                                 maxnames, flags);
@@ -14336,8 +14340,9 @@ static void virDomainSnapshotObjListCount(void
*payload,
     virDomainSnapshotObjPtr obj = payload;
     struct virDomainSnapshotNumData *data = opaque;

-    /* LIST_ROOTS/LIST_DESCENDANTS was handled by caller,
-     * LIST_METADATA is a no-op if we get this far.  */
+    /* LIST_ROOTS/LIST_DESCENDANTS was handled by the choice of
+     * iteration made in the caller, and LIST_METADATA is a no-op if
+     * we get this far.  */
     if ((data->flags & VIR_DOMAIN_SNAPSHOT_LIST_LEAVES) && obj->nchildren)
         return;
     data->count++;
@@ -14346,6 +14351,9 @@ static void virDomainSnapshotObjListCount(void
*payload,
 int virDomainSnapshotObjListNum(virDomainSnapshotObjListPtr snapshots,
                                 unsigned int flags)
 {
+    /* LIST_ROOTS and LIST_DESCENDANTS have the same bit value, but
+     * opposite semantics.  Toggle here to get the correct traversal
+     * on the metaroot.  */
     flags ^= VIR_DOMAIN_SNAPSHOT_LIST_ROOTS;
     return virDomainSnapshotObjListNumFrom(&snapshots->metaroot, flags);
 }

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org



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