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Date: Thu, 26 Aug 2010 08:25:36 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] qdev: Reset hotplugged devices
References: <20100803161914.15514.59304.stgit@localhost6.localdomain6>	<m38w41psje.fsf@blackfin.pond.sub.org>	<1282308092.3860.0.camel@x201>	<m3tymp9tgp.fsf@blackfin.pond.sub.org>	<4C6EA5C9.8080700@codemonkey.ws>	<20100825030752.GA14605@valinux.co.jp>
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, Isaku Yamahata <yamahata@valinux.co.jp>, Alex Williamson <alex.williamson@redhat.com>, glommer@redhat.com, Markus Armbruster <armbru@redhat.com>

On 08/26/2010 08:15 AM, Avi Kivity wrote:
>  On 08/25/2010 03:55 PM, Anthony Liguori wrote:
>>
>>> Maybe we can merge the patches.
>>> As for your patch, I have some comment.
>>> - bus itself may want its own handler. At lease pci bus needs it.
>>>    And propagating reset signal to children is up to the bus 
>>> controller.
>>
>> I disagree.  Reset should be equivalent to power off + init and it's 
>> not something that can be selectively propagated.
>
> Not all busses propagate reset - SCSI is an example (I think).
>

We're talking about cold reset vs. warm reset.

In the absence of passthrough, I'm struggling to see a useful use-case 
with warm reset.  However, there are many useful things we can do 
assuming a cold reset (like MADV_DONTNEED memory on reboot).

That's not saying we shouldn't do a warm reset, but I'd like to see that 
as an incremental addition to what we have today (like introducing a 
propagating warm reset callback) and thinking through what the actual 
behavior should and shouldn't be.

Regards,

Anthony Liguori