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

[Paolo Bonzini]

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