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Re: [Qemu-devel] virtio-9p: hot-plug/unplug about virtio-9p device
From: |
Greg Kurz |
Subject: |
Re: [Qemu-devel] virtio-9p: hot-plug/unplug about virtio-9p device |
Date: |
Fri, 12 Jan 2018 11:48:19 +0100 |
On Thu, 11 Jan 2018 10:23:32 +0800
sochin.jiang <address@hidden> wrote:
> On 2018/1/8 18:10, Greg Kurz wrote:
> > On Tue, 19 Dec 2017 13:41:12 +0800
> > sochin.jiang <address@hidden> wrote:
> >
> >> Hi, guys.
> >>
> >> I'm looking for the hot-plug/unplug features of virtio-9p device
> >> recently, and found there's a lack of support.
> >>
> >> I am wondering why ? Is there a reason. Actually, I write a qmp
> >> command to support fsdev_add, then a device_add qmp will
> >>
> >> successfully add a virtio-9p device(just like virtio-blk).
> >>
> >> Whether there is some concerns that we haven't support this ? hope for
> >> a reply, thanks.
> >>
> >>
> >> sochin.
> >>
> > Hi Sochin,
> >
> > I've just discovered this mail by chance. Please note I'm the only active
> > maintainer for virtio-9p. You really should check the content of MAINTAINERS
> > and Cc the appropriate people. :)
> >
> > Now, back to your question. Yes, there's only some partial support for
> > hot-plug/unplug. Mostly because nobody cared to work on it I guess.
> >
> > So, indeed, we don't have fsdev_add/fsdev_del, ie, we can only rely on
> > shared directories specified on the QEMU command line.
> >
> > On the virtio-9p device side, hotplug is supported, ie, device_add virtio-9p
> > works as expected.
> >
> > Hot-unplug is different as it requires some coordination with the guest. The
> > current status is that it requires the 9p shared directory to be unmounted
> > in the guest: if you do device_del while the directory is mounted in a linux
> > guest, you'll get these messages in the guest syslog:
> >
> > kernel:9pnet_virtio virtio2: p9_virtio_remove: waiting for device in use.
> >
> > If the 9p directory is unmounted at some point, then the hot unplug
> > sequence will eventually succeed.
> >
> > But this shouldn't be done like this: the guest should cancel inflight
> > requests and cause any new I/O requests in the guest to fail right away.
> > I have a tentative patch for the linux driver I can share if you want.
> >
> > Cheers,
> >
> > --
> > Greg
> >
> > .
> >
>
>
> Thanks, Greg.
>
> Indeed, I got those error messages while trying to do device_del with
> shared directory mounted in the guest. I really would like to see you patch
> for linux driver.
>
I'll try to send it soon.
> About virtio-9p, we are actually considering to use it for hypervisor-based
> container,
Something like Intel's Clear Containers ?
> a support of hotplug/unplug will be better, also I believe there will be more
> people to work on it.
That's good news !
Cheers,
--
Greg
>
>
> Sochin.
>
>
>