Re: [Qemu-devel] Some confusion about live migration of usb device

[gerd hoffmann]

On Thu, Sep 06, 2018 at 10:23:45PM +0800, CheneyLin wrote:
> 
> 
> 
> > -----原始邮件-----
> > 发件人: "gerd hoffmann" <address@hidden>
> > 发送时间: 2018-09-06 21:52:23 (星期四)
> > 收件人: linzhecheng <address@hidden>
> > 抄送: "wangxin (U)" <address@hidden>, CheneyLin <address@hidden>, 
> > "address@hidden" <address@hidden>
> > 主题: Re: [Qemu-devel] Some confusion about live migration of usb device
> > 
> > On Thu, Sep 06, 2018 at 12:10:08PM +0000, linzhecheng wrote:
> > > You had said that copying vmstate of usb-host is pointless, so just 
> > > unpulg and plug it after migration is all right,
> > >  but will other usb devices like usb-storage devices lose pending 
> > > USBPackets then?  
> > 
> > Ah, emulated usb devices.  The usb host adapters will re-submit any
> > unfinished usb transfers on the target machine.
> You mean target vm usb controllers will re-submit them? 

Yes.

> And what about usb-redir, btw?

Basically the same.  But some extra care is needed to make sure the
physical device will not see requests twice when the target starts
replaying unfinished requests.  All usb requests get a unique tag
(USBPacket->id) so the usbredir server (typically spice client) has a
chance to handle this correctly.

cheers,
  Gerd