Re: [PATCH v17 02/14] dm-linear: Report to the block layer that the write order is preserved

[Bart Van Assche <bvanassche@acm.org>]

On 1/17/25 10:04 AM, Mikulas Patocka wrote:
> What if you have multiple linear targets in a table? Then, the write order
> would not be preserved.

If dm-linear is used on top of zoned storage, shouldn't each target
involve a whole number of zones? Doesn't this mean that dm-linear will
preserve the write order per zone?

> How is write pipelining supposed to work with suspend/resume? dm doesn't
> preserve the order of writes in case of suspend.

That's an interesting question. I expect that the following will happen
upon resume if zoned writes would have been reordered by dm-linear:
* The block device reports one or more unaligned write errors.
* For the zones for which an unaligned write error has been reported,
   the flag BLK_ZONE_WPLUG_ERROR is set (see also patch 07/14 in this
   series).
* Further zoned writes are postponed for the BLK_ZONE_WPLUG_ERROR zones
   until all pending zoned writes have completed.
* Once all pending zoned writes have completed for a
   BLK_ZONE_WPLUG_ERROR zone, these are resubmitted. This happens in LBA
   order.
* The resubmitted writes will succeed unless the submitter (e.g. a
   filesystem) left a gap between the zoned writes. If the submitter
   does not follow the zoned block device specification, the zoned
   writes will be retried until the number of retries has been exhausted.
   Block devices are expected to set the number of retries to a small
   positive number.

Thanks,

Bart.