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Date: Mon, 11 Oct 2010 09:51:14 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] monitor: add usb_detach
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To: Alon Levy <alevy@redhat.com>
Cc: qemu-devel@nongnu.org

On 10/10/10 13:12, Alon Levy wrote:
>
> ----- "Anthony Liguori"<anthony@codemonkey.ws>  wrote:
>
>> How is this different than usb_del?  Is it that it detaches it but
>> does
>> not delete the device?
>
> yes. There is no usb_attach command because it was harder to write (can't
> use the bus.addr since a detached device doesn't have them) and I didn't
> need it right now, my device attaches itself based on a external event.

Which points out a problem with this patch:  It should better not use 
bus.addr.  addr isn't fixed and even can be uninitialized.  Yes, usb_del 
uses it (for historical reasons).  But we better should not use it in 
new code.  Better use the device id (like device_del).  Which will work 
for usb_attach too.

Next question:  What is the use case?  attach/detach is used by devices 
internally.  usb-host does attach/detach when devices get plugged-in and 
-out on the host.  The ccid device does simliar things on vsclient 
connect/disconnect.  So toggeling the attach state via monitor easily 
could have unwanted side effects ...

cheers,
   Gerd