linux-kernel - Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

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Date:   Fri, 8 Jul 2022 15:51:38 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Eugenio Perez Martin <eperezma@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>, Jason Wang <jasowang@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        kvm list <kvm@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Cindy Lu <lulu@...hat.com>,
        "Kamde, Tanuj" <tanuj.kamde@....com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        "Uminski, Piotr" <Piotr.Uminski@...el.com>,
        habetsm.xilinx@...il.com, "Dawar, Gautam" <gautam.dawar@....com>,
        Pablo Cascon Katchadourian <pabloc@...inx.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>,
        Laurent Vivier <lvivier@...hat.com>,
        Longpeng <longpeng2@...wei.com>,
        Dinan Gunawardena <dinang@...inx.com>,
        Martin Petrus Hubertus Habets <martinh@...inx.com>,
        Martin Porter <martinpo@...inx.com>,
        Eli Cohen <elic@...dia.com>, ecree.xilinx@...il.com,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Harpreet Singh Anand <hanand@...inx.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Zhang Min <zhang.min9@....com.cn>
Subject: Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

On Fri, Jul 08, 2022 at 01:38:45PM +0200, Eugenio Perez Martin wrote:
>On Tue, Jun 28, 2022 at 3:43 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
>>
>> On Thu, Jun 23, 2022 at 06:07:36PM +0200, Eugenio Pérez wrote:
>> >Userland knows if it can suspend the device or not by checking this feature
>> >bit.
>> >
>> >It's only offered if the vdpa driver backend implements the suspend()
>> >operation callback, and to offer it or userland to ack it if the backend
>> >does not offer that callback is an error.
>>
>> Should we document in the previous patch that the callback must be
>> implemented only if the drive/device support it?
>>
>
>It's marked as optional in the doc, following other optional callbacks
>like set_group_asid for example. But I'm ok with documenting this
>behavior further.
>
>> The rest LGTM although I have a doubt whether it is better to move this
>> patch after patch 3, or merge it with patch 3, for bisectability since
>> we enable the feature here but if the userspace calls ioctl() with
>> VHOST_VDPA_SUSPEND we reply back that it is not supported.
>>
>
>I'm fine with moving it, but we will have that behavior with all the
>devices anyway. Regarding userspace, we just replace ENOIOCTL with
>EOPNOTSUPP. Or I'm missing something?

Yep, you're right, this is fine! ;-)

Stefano