Re: [Qemu-devel] [question] live migration about redir-usb

[linzhecheng <linzhecheng@huawei.com>]

> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@redhat.com]
> Sent: Monday, November 26, 2018 4:50 PM
> To: linzhecheng <linzhecheng@huawei.com>
> Cc: qemu-devel@nongnu.org; wangxin (U) <wangxinxin.wang@huawei.com>;
> Zhoujian (jay) <jianjay.zhou@huawei.com>
> Subject: Re: [Qemu-devel] [question] live migration about redir-usb
> 
> On Mon, Nov 26, 2018 at 06:53:23AM +0000, linzhecheng wrote:
> >
> >
> > > -----Original Message-----
> > > From: Gerd Hoffmann [mailto:kraxel@redhat.com]
> > > Sent: Monday, November 26, 2018 2:46 PM
> > > To: linzhecheng <linzhecheng@huawei.com>
> > > Cc: qemu-devel@nongnu.org; wangxin (U)
> <wangxinxin.wang@huawei.com>;
> > > Zhoujian (jay) <jianjay.zhou@huawei.com>
> > > Subject: Re: [Qemu-devel] [question] live migration about redir-usb
> > >
> > > On Mon, Nov 26, 2018 at 02:29:12AM +0000, linzhecheng wrote:
> > > > Hi, Gerd
> > > > I have read this discussion thread about live migration in tcp mode.
> > > > https://bugzilla.redhat.com/show_bug.cgi?id=1254971
> > > > Only spice redirection supports live migration not, but why not tcp mode?
> > > > Does usbredirserver not support it or qemu?
> > >
> > > usbredirserver.
> > >
> > > spice client holds a connection to both source and target host for a
> > > seamless connection handover, and usb-redir needs that too to hand
> > > over the usb device without interruption.
> > >
> > > usbredirserver can't do that.
> 
> > So if we realize the handover between src and dst chardev of qemu, we
> > can do live migration in tcp mode.
> 
> > Is it similar with openvswtich who both accept the connection of src and dst
> qemu?
> 
> It is more complicated than just accepting two connections.  Network can just
> throw away packages if needed, typicaly they will be resent by the guest.  That
> doesn't work with usb, you must properly keep track of every in-flight usb
> transfer.
Why will network throw away packets? I think inflight usb
 Packets have already been tracked by redir-usb in live migration. What's more do we have to do?

> 
> What exactly do you want do?
Realize live migration for redir-usb in tcp mode.
> 
> Maybe it will be simpler to build a stripped-down spice client with only the usb
> redir code, which doesn't require a UI and which you can start from the
> command line like usbredirserver?  Most spice client code is actually in shared
> libraries, so it should not be too much work.
> 
> cheers,
>   Gerd