Hi Tomasz,

On 03/05/2018 04:59 PM, Tomasz Kulasek wrote:
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.


Signed-off-by: Dariusz Stojaczyk <dariuszx.stojac...@intel.com>
Signed-off-by: Tomasz Kulasek <tomaszx.kula...@intel.com>
---
  lib/librte_vhost/rte_vhost.h | 24 ++++++++++++++++++++++++
  lib/librte_vhost/vhost.c     | 27 +++++++++++++++++++++++++++
  2 files changed, 51 insertions(+)


I agree with the patch, but it is missing the declaration of the new API
in rte_vhost_version.map.

Thanks,
Maxime

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