With upcoming event index patch we will need
to keep track of how many descriptor chains we
have really put into the avail vring. This patch
is a step towards that.
Our virtio layer abstracts away descriptor chains
as "requests". We can start requests, add descriptors
to them, and finally flush them. So far we used to put
any descriptors directly into the virtqueue desc ring,
and made them visible to the device only through
virtqueue_req_flush().
All of our virtio bdev modules currently flush the
virtqueue after adding each single request, but the
docs for the virtio API say it's possible to start
multiple subsequent requests and flush them all at
once. This was conceptually broken so far and only
the last request would be exposed to the device.
It's now fixed and subsequent requests are put
into the avail vring as soon as they're complete
(either the next request is started, or the
virtqueue is flushed).
Change-Id: I76b7db88ab094c38430edd8ff0e65681775dcb31
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/415590
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
587002f511