From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: Re: [PATCH] vhost: add API for getting last_idx of vrings
Date: Wed, 28 Mar 2018 10:57:14 +0200
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References: <20180305155959.21212-1-tomaszx.kulasek@intel.com>
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Cc: daniel.verkamp@intel.com, james.r.harris@intel.com,
 pawelx.wodkowski@intel.com, dev@dpdk.org,
 Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
To: Tomasz Kulasek <tomaszx.kulasek@intel.com>, yliu@fridaylinux.org
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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.stojaczyk@intel.com>
> Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@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