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From: Markus Armbruster <armbru@redhat.com>
References: <20110601181255.077fb5fd@doriath> <4DE6B087.6010708@codemonkey.ws>
Date: Mon, 06 Jun 2011 13:13:07 +0200
In-Reply-To: <4DE6B087.6010708@codemonkey.ws> (Anthony Liguori's message of
	"Wed, 01 Jun 2011 16:35:03 -0500")
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Subject: Re: [Qemu-devel] QMP: RFC: I/O error info & query-stop-reason
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, jdenemar@redhat.com, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>

Anthony Liguori <anthony@codemonkey.ws> writes:

> On 06/01/2011 04:12 PM, Luiz Capitulino wrote:
>> Hi there,
>>
>> There are people who want to use QMP for thin provisioning. That's, the VM is
>> started with a small storage and when a no space error is triggered, more space
>> is allocated and the VM is put to run again.
>>
>> QMP has two limitations that prevent people from doing this today:
>>
>> 1. The BLOCK_IO_ERROR doesn't contain error information
>>
>> 2. Considering we solve item 1, we still have to provide a way for clients
>>     to query why a VM stopped. This is needed because clients may miss the
>>     BLOCK_IO_ERROR event or may connect to the VM while it's already stopped
>>
>> A proposal to solve both problems follow.
>>
>> A. BLOCK_IO_ERROR information
>> -----------------------------
>>
>> We already have discussed this a lot, but didn't reach a consensus. My solution
>> is quite simple: to add a stringfied errno name to the BLOCK_IO_ERROR event,
>> for example (see the "reason" key):
>>
>> { "event": "BLOCK_IO_ERROR",
>>     "data": { "device": "ide0-hd1",
>>               "operation": "write",
>>               "action": "stop",
>>               "reason": "enospc", }
>
> you can call the reason whatever you want, but don't call it
> stringfied errno name :-)

Care to explain why?