Re: [PATCH 3/3] qemuSnapshotCreate: Don't insert snapshot into list with VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA

[Peter Krempa]

On Tue, Jan 11, 2022 at 15:53:22 +0100, Michal Prívozník wrote:
> On 1/11/22 10:53, Peter Krempa wrote:

[...]

> > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2039131
> > Signed-off-by: Peter Krempa 
> > ---
> >  src/qemu/qemu_snapshot.c | 25 +++--
> >  1 file changed, 15 insertions(+), 10 deletions(-)
> > 
> > diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
> > index 9a5d3e60aa..e9fc9051c1 100644
> > --- a/src/qemu/qemu_snapshot.c
> > +++ b/src/qemu/qemu_snapshot.c
> > @@ -1756,7 +1756,7 @@ qemuSnapshotCreate(virDomainObj *vm,
> > virQEMUDriverConfig *cfg,
> > unsigned int flags)
> >  {
> > -
> > +g_autoptr(virDomainMomentObj) noMetadataSnap = NULL;
> 
> Nitpick, this variable is used as a bool later, which creates double
> negative conditions like !noMetadataSnap. But I'm failing to suggest
> anything better.

I went with 'tmpsnap'. It is indeed temporary ;)

Re: [PATCH 3/3] qemuSnapshotCreate: Don't insert snapshot into list with VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA

[Michal Prívozník]

On 1/11/22 10:53, Peter Krempa wrote:
> Our approach to snapshots without metadata was to insert them to the
> snapshot list and then later remove them from the list when the flag is
> present.
> 
> This quirky logic was broken in a recent refactor of the snapshot code
> causing that the snapshot stayed inserted in the snapshot list.
> 
> Recent refactor of the snapshot code didn't faithfully relocate this
> logic to the new function.
> 
> Rather than attempting to restore the quirky logic of adding and then
> removing the object, don't add the snapshot into the list at all when
> the user doesn't want metadata.
> 
> We achieve this by creating a temporary 'virDomainMomentObj' wrapper
> which is not inserted into the list and using that instead of calling
> virDomainSnapshotAssignDef.
> 
> Fixes: 9bad0fb809b
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2039131
> Signed-off-by: Peter Krempa 
> ---
>  src/qemu/qemu_snapshot.c | 25 +++--
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
> index 9a5d3e60aa..e9fc9051c1 100644
> --- a/src/qemu/qemu_snapshot.c
> +++ b/src/qemu/qemu_snapshot.c
> @@ -1756,7 +1756,7 @@ qemuSnapshotCreate(virDomainObj *vm,
> virQEMUDriverConfig *cfg,
> unsigned int flags)
>  {
> -
> +g_autoptr(virDomainMomentObj) noMetadataSnap = NULL;

Nitpick, this variable is used as a bool later, which creates double
negative conditions like !noMetadataSnap. But I'm failing to suggest
anything better.

Michal

[PATCH 3/3] qemuSnapshotCreate: Don't insert snapshot into list with VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA

[Peter Krempa]

Our approach to snapshots without metadata was to insert them to the
snapshot list and then later remove them from the list when the flag is
present.

This quirky logic was broken in a recent refactor of the snapshot code
causing that the snapshot stayed inserted in the snapshot list.

Recent refactor of the snapshot code didn't faithfully relocate this
logic to the new function.

Rather than attempting to restore the quirky logic of adding and then
removing the object, don't add the snapshot into the list at all when
the user doesn't want metadata.

We achieve this by creating a temporary 'virDomainMomentObj' wrapper
which is not inserted into the list and using that instead of calling
virDomainSnapshotAssignDef.

Fixes: 9bad0fb809b
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2039131
Signed-off-by: Peter Krempa 
---
 src/qemu/qemu_snapshot.c | 25 +++--
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
index 9a5d3e60aa..e9fc9051c1 100644
--- a/src/qemu/qemu_snapshot.c
+++ b/src/qemu/qemu_snapshot.c
@@ -1756,7 +1756,7 @@ qemuSnapshotCreate(virDomainObj *vm,
virQEMUDriverConfig *cfg,
unsigned int flags)
 {
-
+g_autoptr(virDomainMomentObj) noMetadataSnap = NULL;
 virDomainMomentObj *snap = NULL;
 virDomainMomentObj *current = NULL;
 virDomainSnapshotPtr ret = NULL;
@@ -1767,16 +1767,20 @@ qemuSnapshotCreate(virDomainObj *vm,
 if (qemuSnapshotPrepare(vm, def, ) < 0)
 return NULL;

-if (!(snap = virDomainSnapshotAssignDef(vm->snapshots, def)))
-return NULL;
-
-virObjectRef(def);
+if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA) {
+snap = noMetadataSnap = virDomainMomentObjNew();
+snap->def = >parent;
+} else {
+if (!(snap = virDomainSnapshotAssignDef(vm->snapshots, def)))
+return NULL;

-current = virDomainSnapshotGetCurrent(vm->snapshots);
-if (current) {
-snap->def->parent_name = g_strdup(current->def->name);
+if ((current = virDomainSnapshotGetCurrent(vm->snapshots))) {
+snap->def->parent_name = g_strdup(current->def->name);
+}
 }

+virObjectRef(def);
+
 /* actually do the snapshot */
 if (virDomainObjIsActive(vm)) {
 if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY ||
@@ -1804,7 +1808,7 @@ qemuSnapshotCreate(virDomainObj *vm,
 }
 }

-if (!(flags & VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA)) {
+if (!noMetadataSnap) {
 qemuSnapshotSetCurrent(vm, snap);

 if (qemuSnapshotCreateWriteMetadata(vm, snap, driver, cfg) < 0)
@@ -1818,7 +1822,8 @@ qemuSnapshotCreate(virDomainObj *vm,
 return ret;

  error:
-virDomainSnapshotObjListRemove(vm->snapshots, snap);
+if (!noMetadataSnap)
+virDomainSnapshotObjListRemove(vm->snapshots, snap);
 return NULL;
 }

-- 
2.31.1