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[Qemu-devel] Re: virtio: Add memory statistics reporting to the balloon

From: Juan Quintela
Subject: [Qemu-devel] Re: virtio: Add memory statistics reporting to the balloon driver (V8)
Date: Tue, 09 Mar 2010 14:51:31 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Adam Litke <address@hidden> wrote:
> The changes in V8 of this patch are related to the monitor infrastructure.  No
> changes to the virtio interface core have been made since V4.  This is 
> intended
> to apply on top of my API for asynchronous monitor commands patch.

I know that I am late reviewing this.  Once told that, it has some
issues with migration.

>  typedef struct VirtIOBalloon
>  {


> +    MonitorCompletion *stats_callback;

Notice this stats_callback.

typedef void (MonitorCompletion)(void *opaque, QObject *ret_data);

> +    void *stats_opaque_callback_data;
>  } VirtIOBalloon;

It don't update the version field, should be two (that is easy to fix).

>      qemu_put_be32(f, s->num_pages);
>      qemu_put_be32(f, s->actual);
> +    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_elem,
>      sizeof(VirtQueueElement));

We send a struct directly, migration inter-architectures is broken (not
that virtio drivers in general are good here).

> +    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
> +    qemu_put_buffer(f, (uint8_t *)&s->stats_callback,
> sizeof(MonitorCompletion));

We send a pointer to one function.

> +    qemu_put_buffer(f, (uint8_t *)&s->stats_opaque_callback_data,
> sizeof(void));

And a pointer to one opaque.

Any recompilation/etc would break migration.  I have tried to understand
what happened with monitor async commands, and my head exploded in

Is there any written explanation of what are we trying to do here?

Later, Juan.

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