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

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Message-ID: <CACycT3uw6KJgTo+dBzSj07p2P_PziD+WBfX4yWVX-nDNUD2M3A@mail.gmail.com>
Date:   Tue, 1 Dec 2020 17:55:41 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.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 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.

Thanks,
Yongji