vhost-net devices might keep track of last descriptors indices by
themselves, and assuming they initially start at 0, but that is not the
case for vhost-scsi. Initial last descriptor indices are set via
VHOST_USER_SET_VRING_BASE message, and we cannot possibly predict what
will they be. Setting these to vqueue->used->idx is also not an option,
because there might be some yet unprocessed requests between these and
the actual last_idx. This patch adds API for getting/setting last
descriptor indices of vrings, so that they can be synchronized between
user-device and rte_vhost.
The last_idx flow could be as following:
* vhost start
* received SET_VRING_BASE msg, last_idx is set on rte_vhost side
* created user-device, last_idx pulled from rte_vhost
* requests are being processed by user-device, last_idx changes
* destroyed user-device, last_idx pushed to rte_vhost
* *at this point, vrings could be recreated and another SET_VRING_BASE
message could arrive, so last_idx would be set*
* recreated user-device, last_idx pulled from rte_vhost
Change-Id: I247ba4e461a2a2b524ccade364f5b7bf260f7538
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
52b10970c4