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Date: Mon, 06 Jun 2011 17:54:53 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 05/18] ide: Turn debug messages into
	assertions
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To: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org

Am 01.06.2011 15:44, schrieb Luiz Capitulino:
> On Thu, 26 May 2011 18:12:08 -0300
> Luiz Capitulino <lcapitulino@redhat.com> wrote:
> 
>> On Thu, 19 May 2011 14:33:19 +0200
>> Kevin Wolf <kwolf@redhat.com> wrote:
>>
>>> These printfs aren't really debug messages, but clearly indicate a bug if they
>>> ever become effective.
>>
>> Then we have a bug somewhere, starting a VM with:
>>
>>  # qemu -hda disks/test.img -enable-kvm -m 1G -cdrom /dev/sr0
>>
>> Where the host's CDROM is empty, triggers one of these asserts:
>>
>>  qmp-unstable/hw/ide/pci.c:299: bmdma_cmd_writeb: Assertion `bm->bus->dma->aiocb == ((void *)0)'
> 
> I found out why this is happening. I'm passing '-snapshot' to the command-line,
> sorry for not mentioning it (I forgot I was using my devel alias).

Okay, so I think we have at least two problems here:

* qcow2 doesn't implement bdrv_is_inserted, so the IDE emulation thinks
  there is a medium when there isn't. Reading produces only errors.

* This seems to be an error case where bdrv_aio_readv fails
  immediately. In this case, qcow2 calls the callback directly, but it
  should use a bottom half. This leads to an unexpected state in IDE
  and lets the assertion fail.

I think we must fix the latter. Not sure what to do about the former,
it's probably similar to forwarding bdrv_eject().

Kevin