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Old 09-25-2012, 09:34 PM
"Kasatkin, Dmitry"
 
Default bufio & write completion indication

Hi,

I have a question.

How dm target can be sure that data really have been written to storage?

- for remaped request
bio_end really indicates that?
or data can be stuck in block buffers?

- for bufio requests
dm_bufio_write_dirty_buffers() provides that ?


Thanks,
Dmitry

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Old 09-25-2012, 11:07 PM
Mikulas Patocka
 
Default bufio & write completion indication

On Wed, 26 Sep 2012, Kasatkin, Dmitry wrote:

> Hi,
>
> I have a question.
>
> How dm target can be sure that data really have been written to storage?
>
> - for remaped request
> bio_end really indicates that?
> or data can be stuck in block buffers?

No. When bio_endio is called, data may still be in hardware cache in the
disk and not yet written to the disk. After you receive bio_endio for a
write bio, you must submit another bio with REQ_FLUSH flag to flush the
hardware cache (or you can use blkdev_issue_flush to send it).

> - for bufio requests
> dm_bufio_write_dirty_buffers() provides that ?

Yes. dm_bufio_write_dirty_buffers calls dm_bufio_issue_flush and
dm_bufio_issue_flush flushes the hardware cache.

Mikulas

>
> Thanks,
> Dmitry
>

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