Re: [Qemu-devel] [RFC] virtio: Report new guest memory statistics pertinent to memory ballooning (V2)

[Jamie Lokier]

Adam Litke wrote:
> +        s->stats.pswapin = has_feature(dev, VIRTIO_BALLOON_F_RPT_SWAP_OUT) ?
> +                                       dev->stats.pswapin : -1;

(etc.)

Why not simply have the guest fill in the unused fields with -1, and
say that's how "no meaningful value" is represented in the ABI?

All guests have to know about all those fields anyway, for the
structure layout.  Is there any benefit to specifying feature bits in
advance over simply storing -1 there?

-- Jamie