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

[linzhecheng]

> -----Original Message-----
> From: gerd hoffmann [mailto:address@hidden
> Sent: Friday, September 07, 2018 2:23 PM
> To: CheneyLin <address@hidden>
> Cc: linzhecheng <address@hidden>; wangxin (U)
> <address@hidden>; address@hidden
> Subject: Re: [Qemu-devel] Some confusion about live migration of usb device
> 
> 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.
I got it! Thank you for patiently answering my questions.
> 
> cheers,
>   Gerd