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From: John Snow <jsnow@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 2/2] atapi migration: Throw recoverable error to avoid recovery
Date: Thu, 18 Dec 2014 18:42:53 -0500	[thread overview]
Message-ID: <5493667D.60107@redhat.com> (raw)
In-Reply-To: <20141218193904.GM4744@work-vm>



On 12/18/2014 02:39 PM, Dr. David Alan Gilbert wrote:
> * Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
>> * Paolo Bonzini (pbonzini@redhat.com) wrote:
>>>
>>>
>>> On 09/12/2014 19:15, Dr. David Alan Gilbert (git) wrote:
>>>> (With the previous atapi_dma flag recovery)
>>>> If migration happens between the ATAPI command being written and the
>>>> bmdma being started, the DMA is dropped.  Eventually the guest times
>>>> out and recovers, but that can take many seconds.
>>>> (This is rare, on a pingpong reading the CD continuously I hit
>>>> this about ~1/30-1/50 migrates)
>>>>
>>>> I don't think we've got enough state to be able to recover safely
>>>> at this point, so I throw a 'medium error, no seek complete'
>>>> that I'm assuming guests will try and recover from an apparently
>>>> dirty CD.
>>>
>>
>>> Also, what is the ATAPI command that is being run?
>>
>> The command in my test case is:
>> 28 00 00 06 df b8 00 00 40 00 00 00
>> so just a standard READ (10); I guess it's possible that other OSs/operations
>> maybe doing different READ variants.
>>
>>> What is the part of the state that is not being migrated?
>>
>> I can't see lba, io_buffer_index, io_buffer_size or cd_sector_size being passed
>> to a VMSTATE_ macro; and having noticed that those are missing I didn't dig much
>> deeper.
>> (I'll admit to not really understanding the interaction between the core.c, atapi.c
>> and pci.c dma code properly to know if it can be reconstructed).
>
> Actually, another argument for this is that even if we come along and add
> the extra state as a subsection, we can still do this as a fallback when receiving
> older streams.
>

Fair enough. I vote we give this hack a shot for now, then. I can always 
put this in my basket of things to look at ($later) after I have 
finished ($other_things).

  reply	other threads:[~2014-12-18 23:43 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-09 18:15 [Qemu-devel] [PATCH 0/2] ATAPI migration fix/hack Dr. David Alan Gilbert (git)
2014-12-09 18:15 ` [Qemu-devel] [PATCH 1/2] Restore atapi_dma flag across migration Dr. David Alan Gilbert (git)
2014-12-10  5:04   ` John Snow
2014-12-09 18:15 ` [Qemu-devel] [PATCH 2/2] atapi migration: Throw recoverable error to avoid recovery Dr. David Alan Gilbert (git)
2014-12-10  6:14   ` John Snow
2014-12-10 12:05     ` Dr. David Alan Gilbert
2014-12-10 20:09     ` Dr. David Alan Gilbert
2014-12-10 22:04   ` Paolo Bonzini
2014-12-11 19:45     ` Dr. David Alan Gilbert
2014-12-18 19:39       ` Dr. David Alan Gilbert
2014-12-18 23:42         ` John Snow [this message]
2015-01-16 17:28   ` John Snow
2015-02-02 12:11     ` Kevin Wolf
2015-01-07 16:26 ` [Qemu-devel] [PATCH 0/2] ATAPI migration fix/hack Dr. David Alan Gilbert
2015-01-30 16:07   ` Dr. David Alan Gilbert

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