[libvirt] [PATCH 03/16] snapshot: Create virDomainMoment base class

[John Ferlan]

On 3/20/19 1:40 AM, Eric Blake wrote:
> Upcoming patches want to add virDomainCheckpoint that behaves very
> similarly to virDomainSnapshot; the easiest way to share common code
> is to give both classes a common base class.  Thanks to the accessor
> functions in the previous patch, we have very few changes required
> outside of datatypes.[ch].  The subclass does have to use a dummy
> field, though, to satisfy virobject's insistence on size
> differentiation for type safety.
> 
> Note that virClassNew() supports a NULL dispose method for a class
> that has nothing to clean up, but VIR_CLASS_NEW has no easy way to
> register such a class without a #define hack.
> 
> I promised my teenage daughter Evelyn that I'd give her credit for her
> contribution to this commit. I asked her "What would be a good name
> for a base class for DomainSnapshot and DomainCheckpoint". After
> explaining what a base class was (using the classic OOB Square and
> Circle inherit from Shape), she came up with "DomainMoment", which is
> way better than my initial thought of "DomainPointInTime" or
> "DomainPIT".

Maybe it was her way to ensure some sort of "mom" 'ent'ry got included
into libvirt ;-}

> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/datatypes.h               |  26 ++++++--
>  src/datatypes.c               | 110 ++++++++++++++++++++--------------
>  src/libvirt-domain-snapshot.c |   2 +-
>  3 files changed, 88 insertions(+), 50 deletions(-)
> 

[...]

> 
> 
> +/**
> + * virGetDomainMoment:
> + * @domain: the domain involved in a point-in-time moment
> + * @name: pointer to the domain moment name

 * @subclass: Either virDomainSnapshotClass or virDomainCheckpointClass

[ok that second one is eventually.... and it's only internal so
validation is left to the developer ;-}]

> + *
> + * Allocates a new concrete subclass of a domain moment object. When
> + * the object is no longer needed, virObjectUnref() must be called in
> + * order to not leak data.
> + *
> + * Returns a pointer to the domain moment object, or NULL on error.
> + */
> +static virDomainMomentPtr
> +virGetDomainMoment(virDomainPtr domain, const char *name, virClassPtr subclass)
> +{
> +    virDomainMomentPtr ret = NULL;
> +
> +    if (virDataTypesInitialize() < 0)
> +        return NULL;
> +
> +    virCheckDomainGoto(domain, error);
> +    virCheckNonNullArgGoto(name, error);
> +
> +    if (!(ret = virObjectNew(subclass)))
> +        goto error;
> +    if (VIR_STRDUP(ret->name, name) < 0)
> +        goto error;
> +
> +    ret->domain = virObjectRef(domain);
> +
> +    return ret;
> +
> + error:
> +    virObjectUnref(ret);
> +    return NULL;
> +}
> +
> +

Reviewed-by: John Ferlan <jferlan at redhat.com>

John

I have to say I did pause to stop and think about the Dispose thing...
Especially with the "parent" class having a NULL ->dispose, but also
having a klass->parent which would have the MomentDispose.


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