Re: [Qemu-block] [Qemu-devel] [PATCH 2/6] libqos: add virtio used ring support

[Fam Zheng]

On Wed, 06/28 19:47, Stefan Hajnoczi wrote:
> Existing tests do not touch the virtqueue used ring.  Instead they poll
> the virtqueue ISR register and peek into their request's device-specific
> status field.
> 
> It turns out that the virtqueue ISR register can be set to 1 more than
> once for a single notification (see commit
> 83d768b5640946b7da55ce8335509df297e2c7cd "virtio: set ISR on dataplane
> notifications").  This causes problems for tests that assume a 1:1
> correspondence between the ISR being 1 and request completion.
> 
> Peeking at device-specific status fields is also problematic if the
> device has no field that can be abused for EINPROGRESS polling
> semantics.  This is the case if all the field's values may be set by the
> device; there's no magic constant left for polling.
> 
> It's time to process the used ring for completed requests, just like a
> real virtio guest driver.  This patch adds the necessary APIs.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Fam Zheng <address@hidden>