[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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: Mon, 8 Jan 2018 11:10:39 +0100

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.



reply via email to

[Prev in Thread] Current Thread [Next in Thread]