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SubjectRe: [PATCH v3 0/6] virtio_balloon: virtio 1 support
On Tue, 14 Apr 2015 11:21:11 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index f81b220..164e0c2 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -52,15 +52,31 @@ struct virtio_balloon_config {
> #define VIRTIO_BALLOON_S_MEMTOT 5 /* Total amount of memory */
> #define VIRTIO_BALLOON_S_NR 6
>
> +/*
> + * Memory statistics structure.
> + * Driver fills an array of these structures and passes to device.
> + *
> + * NOTE: fields are laid out in a way that would make compiler add padding
> + * between and after fields, so we have to use compiler-specific attributes to
> + * pack it, to disable this padding. This also often causes compiler to
> + * generate suboptimal code.
> + *
> + * We maintain this for backwards compatibility, but don't follow this example.

s/this/the existing statistics structure/

> + *
> + * Do something like the below instead:

If you want to implement a similar structure, do...

Just that nobody gets the idea that they are supposed to implement new
balloon statistics ;)

> + * struct virtio_balloon_stat {
> + * __virtio16 tag;
> + * __u8 reserved[6];
> + * __virtio64 val;
> + * };

(...)

> @@ -225,13 +219,8 @@ static inline void update_stat(struct virtio_balloon *vb, int idx,
> u16 tag, u64 val)
> {
> BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
> - if (virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) {
> - vb->stats[idx].tag = cpu_to_le32(tag);
> - vb->stats[idx].val = cpu_to_le64(val);
> - } else {
> - vb->legacy_stats[idx].tag = tag;
> - vb->legacy_stats[idx].val = val;
> - }
> + vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);

Seems that nobody seemed to care much about statistics...

> + vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
> }
>
> #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
>

With these changes merged in:

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>



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