netdev - Re: [External] Re: [PATCH 0/7] Introduce vdpa management tool

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Message-ID: <594b2086-802f-1053-2866-a25d4a327876@redhat.com>
Date:   Wed, 2 Dec 2020 13:48:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     Parav Pandit <parav@...dia.com>,
        virtualization@...ts.linux-foundation.org,
        "Michael S. Tsirkin" <mst@...hat.com>, elic@...dia.com,
        netdev@...r.kernel.org
Subject: Re: [External] Re: [PATCH 0/7] Introduce vdpa management tool


On 2020/12/1 下午5:55, Yongji Xie wrote:
> On Tue, Dec 1, 2020 at 2:25 PM Jason Wang <jasowang@...hat.com> wrote:
>>
>> On 2020/11/30 下午3:07, Yongji Xie wrote:
>>>>> Thanks for adding me, Jason!
>>>>>
>>>>> Now I'm working on a v2 patchset for VDUSE (vDPA Device in Userspace)
>>>>> [1]. This tool is very useful for the vduse device. So I'm considering
>>>>> integrating this into my v2 patchset. But there is one problem：
>>>>>
>>>>> In this tool, vdpa device config action and enable action are combined
>>>>> into one netlink msg: VDPA_CMD_DEV_NEW. But in vduse case, it needs to
>>>>> be splitted because a chardev should be created and opened by a
>>>>> userspace process before we enable the vdpa device (call
>>>>> vdpa_register_device()).
>>>>>
>>>>> So I'd like to know whether it's possible (or have some plans) to add
>>>>> two new netlink msgs something like: VDPA_CMD_DEV_ENABLE and
>>>>> VDPA_CMD_DEV_DISABLE to make the config path more flexible.
>>>>>
>>>> Actually, we've discussed such intermediate step in some early
>>>> discussion. It looks to me VDUSE could be one of the users of this.
>>>>
>>>> Or I wonder whether we can switch to use anonymous inode(fd) for VDUSE
>>>> then fetching it via an VDUSE_GET_DEVICE_FD ioctl?
>>>>
>>> Yes, we can. Actually the current implementation in VDUSE is like
>>> this.  But seems like this is still a intermediate step. The fd should
>>> be binded to a name or something else which need to be configured
>>> before.
>>
>> The name could be specified via the netlink. It looks to me the real
>> issue is that until the device is connected with a userspace, it can't
>> be used. So we also need to fail the enabling if it doesn't opened.
>>
> Yes, that's true. So you mean we can firstly try to fetch the fd
> binded to a name/vduse_id via an VDUSE_GET_DEVICE_FD, then use the
> name/vduse_id as a attribute to create vdpa device? It looks fine to
> me.


Yes, something like this. The anonymous fd will be created during 
dev_add() and the fd will be carried in the msg to userspace.

Thanks


>
> Thanks,
> Yongji
>