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

From: Pavel Butsykin
Subject: Re: [Qemu-devel] [PATCH 1/3] ide: don't loose pending dma state
Date: Thu, 24 Mar 2016 12:24:25 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

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

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).


You mean to do something like that:

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


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