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SubjectRe: [PATCH v2 1/6] virtio_balloon: transitional interface
Date
"Michael S. Tsirkin" <mst@redhat.com> writes:
> Virtio 1.0 doesn't include a modern balloon device.
> But it's not a big change to support a transitional
> balloon device: this has the advantage of supporting
> existing drivers, transparently.

You decided to fix the packed struct...

> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 6a356e3..574267f 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -77,7 +77,7 @@ struct virtio_balloon {
>
> /* Memory statistics */
> int need_stats_update;
> - struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
> + struct virtio_balloon_stat_modern stats[VIRTIO_BALLOON_S_NR];
>
> /* To register callback in oom notifier call chain */
> struct notifier_block nb;
> @@ -269,7 +269,11 @@ static void stats_handle_request(struct virtio_balloon *vb)
> vq = vb->stats_vq;
> if (!virtqueue_get_buf(vq, &len))
> return;
> - sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
> + sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> + else
> + sg_init_one(&sg, &vb->stats->tag, sizeof(vb->stats) -
> + offsetof(typeof(*vb->stats, tag);

This makes it compile, but definitely won't work.

> virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> virtqueue_kick(vq);
> }
> @@ -283,21 +287,30 @@ static void virtballoon_changed(struct virtio_device *vdev)
>
> static inline s64 towards_target(struct virtio_balloon *vb)
> {
> - __le32 v;
> s64 target;
> + u32 num_pages;
>
> - virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages, &v);
> + virtio_cread(vb->vdev, struct virtio_balloon_config,
> + num_pages, &num_pages);
>
> - target = le32_to_cpu(v);
> + /* Legacy balloon config space is LE, unlike all other devices. */
> + if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
> + num_pages = le32_to_cpu((__force le32)num_pages);
> +
> + target = num_pages;
> return target - vb->num_pages;
> }
>
> static void update_balloon_size(struct virtio_balloon *vb)
> {
> - __le32 actual = cpu_to_le32(vb->num_pages);
> + u32 actual = vb->num_pages;
> +
> + /* Legacy balloon config space is LE, unlike all other devices. */
> + if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
> + actual = (__force u32)cpu_to_le32(num_pages);
>
> - virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
> - &actual);
> + virtio_cwrite(vb->vdev, struct virtio_balloon_config,
> + actual, &actual);
> }

Final line is gratitous reformatting.

I would leave the device *exactly* as is, ugly structure packing and
all.

Cheers,
Rusty.


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