Re: [Qemu-devel] [PATCH 1/3] ide: don't loose pending dma state

From: Pavel Butsykin <pbutsykin@virtuozzo.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	"Denis V. Lunev" <den@openvz.org>,
	qemu-devel@nongnu.org
Cc: John Snow <jsnow@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/3] ide: don't loose pending dma state
Date: Thu, 24 Mar 2016 12:24:25 +0300	[thread overview]
Message-ID: <56F3B249.50605@virtuozzo.com> (raw)
In-Reply-To: <56F2FDE5.5020908@redhat.com>

On 23.03.2016 23:34, Paolo Bonzini wrote:
>
>
> On 23/03/2016 11:26, Denis V. Lunev wrote:
>> If the migration occurs after the IDE DMA has been set up but before it
>> has been initiated, the state gets lost upon save/restore. Specifically,
>> ->dma_cb callback gets cleared, so, when the guest eventually starts bus
>> mastering, the DMA never completes, causing the guest to time out the
>> operation.
>>
>> OTOH all the infrastructure is already in place to restart the DMA if
>> the migration happens while the DMA is in progress.
>>
>> So reuse that infrastructure, by calling the DMA callback with an
>> artificial error code in pre_save if the callback is already set but
>> DMAING is clear. The callback then sets bus->error_status to indicate
>> the need for restart; however since DMAING is clear the state upon
>> restore will be exactly "ready forDMA" as before the save.
>
> Could you just use the dma_cmd field to build the error_status?
>
> For extra points, make ide_handle_rw_error convert IDE_DMA_* to
> IDE_RETRY_* so that the callers only need to pass in IDE_RETRY_DMA (like
> they only need to pass in IDE_RETRY_PIO).
>
> Paolo
>
You mean to do something like that:

ide_handle_rw_error(s, -ret, s->dma_cmd | IDE_RETRY_DMA)

?