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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [RFC] virtio: Report new guest memory statistics pertinent to memory ballooning (V2) |
Date: | Mon, 09 Nov 2009 15:15:30 -0600 |
User-agent: | Thunderbird 2.0.0.23 (X11/20090825) |
Jamie Lokier wrote:
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?
Features are negotiated. It lets a host advertise the support of a feature and it lets the guest acknowledge it's support of a feature.
Most importantly, why invent a new mechanism when we already have one? -- Regards, Anthony Liguori
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