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Date: Mon, 11 Oct 2010 07:02:46 -0400 (EDT)
From: Alon Levy <alevy@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] monitor: add usb_detach
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: qemu-devel@nongnu.org


----- "Gerd Hoffmann" <kraxel@redhat.com> wrote:

> 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
> 

debugging. naturally when developing the ccid I had cases where I'd
rather detach the device then bring down qemu. since there is no way
currently to add/remove chardev's from monitor, removing/adding
a device is not enough to reset a device state to the state right
after start.

> could have unwanted side effects ...
> 
> cheers,
>    Gerd