Re: [Qemu-devel] [QEMU PATCH v10 2/3] migration: migrate QTAILQ

[Juan Quintela <quintela@redhat.com>]

Jianjun Duan <duanj@linux.vnet.ibm.com> wrote:
> Currently we cannot directly transfer a QTAILQ instance because of the
> limitation in the migration code. Here we introduce an approach to
> transfer such structures. We created VMStateInfo vmstate_info_qtailq
> for QTAILQ. Similar VMStateInfo can be created for other data structures
> such as list.
>
> This approach will be used to transfer pending_events and ccs_list in spapr
> state.
>
> We also create some macros in qemu/queue.h to access a QTAILQ using pointer
> arithmetic. This ensures that we do not depend on the implementation
> details about QTAILQ in the migration code.
>
> Signed-off-by: Jianjun Duan <duanj@linux.vnet.ibm.com>


> +
> +    trace_get_qtailq(vmsd->name, version_id);
> +    if (version_id > vmsd->version_id) {
> +        error_report("%s %s",  vmsd->name, "too new");
> +        trace_get_qtailq_end(vmsd->name, "too new", -EINVAL);
> +
> +        return -EINVAL;
> +    }
> +    if (version_id < vmsd->minimum_version_id) {
> +        error_report("%s %s",  vmsd->name, "too old");
> +        trace_get_qtailq_end(vmsd->name, "too old", -EINVAL);
> +        return -EINVAL;
> +    }
> +
> +    while (qemu_get_byte(f)) {
> +        elm = g_malloc(size);

I think this is not generic enough.  We really need to allocate a new
element, and then fill it with default values.

virtio list code use it in this way.


Thanks, Juan.