Re: [Qemu-devel] [PATCH] usb-host: insert usb device into hostdevs to be scaned

[CheneyLin]

> -----原始邮件-----
> 发件人: "Gerd Hoffmann" <address@hidden>
> 发送时间: 2018-08-16 21:01:31 (星期四)
> 收件人: linzhecheng <address@hidden>
> 抄送: "wangxin (U)" <address@hidden>, "address@hidden" <address@hidden>
> 主题: Re: [Qemu-devel] [PATCH] usb-host: insert usb device into hostdevs to be 
> scaned
> 
> > > Hmm, needs_autoscan is a fixed property of the device (depending on
> > > configuration), it should not be switched on and off.
> > > 
> > > What problem you are trying to solve?
> > I'm trying to live migrate a vm to local host, but found the host-usb 
> > device was removed then.
> > Is it possible not to remove it after migrating vm?
> 
> Why live-migrate to localhost?  That is rather tricky due to both source
> and target qemu accessing host resources at the same time, and I guess
> this is the reason you are seeing the problems here.
Thanks for your reply, but I'm still confused about these issues:
1. If local live migration is not supported for host-usb device, why we have to 
detach it and
rescan it in usb_host_post_load_bh? If a device's property *needs_autoscan* is 
false, how can we scan it(because
we have detached it)? 
2. Normal live migration between two remote hostes makes a vm access diffrent 
host usb devices, how can
we copy states and data of them? 
> 
> If it is for QA purposes I'd suggest to use two machines for actual live
> migration tests, or store the live migration stream in a file so the two
> qemu instances never run at the same time (this is what "virsh save" is
> doing).
> 
> cheers,
>   Gerd
>