On Tue, Jan 29, 2019 at 12:11:55PM +0800, Stefan Hajnoczi wrote:
> On Tue, Jan 22, 2019 at 04:31:47PM +0800, elohi...@gmail.com wrote:
> > +typedef struct DescState {
> > + uint8_t inuse;
> > + uint8_t version;
> > + uint16_t used_idx;
> > + uint16_t avail_idx;
> > + uint16_t reserved;
> > +} DescState;
> > +
> > +typedef struct QueueRegion {
> > + uint8_t valid;
what's this?
> > + uint16_t desc_num;
there's padding before this field. Pls make it explicit.
> > + DescState desc[0];
> > +} QueueRegion;
> > +
> > +The struct DescState is used to describe one head-descriptor's state. The
> > +fields have following meanings:
> > +
> > + inuse: Indicate whether the descriptor is inuse or not.
inuse by what?
> > +
> > + version: Indicate whether we have an atomic update to used ring and
> > + inflight buffer when slave crash at that point. This field should be
> > + increased by one before and after this two updates. An odd version
> > + indicates an in-progress update.
I'm not sure I understand what does the above say. Also does this
require two atomics? Seems pretty expensive. And why is it called
version?
> > +
> > + used_idx: Store old index of used ring before we update used ring and
> > + inflight buffer so that slave can know whether an odd version inflight
> > + head-descriptor in inflight buffer is processed or not.
Here too.
> > +
> > + avail_idx: Used to preserve the descriptor's order in avail ring so
> > that
> > + slave can resubmit descriptors in order.
Why would that be necessary?
>
> Will a completely new "packed vring" inflight shm layout be necessary to
> support the packed vring layout in VIRTIO 1.1?
>
> https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html#x1-610007
Probably.
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MST
