[Drbd-dev] [PATCH 22/23] drbd: implement REQ_OP_WRITE_ZEROES

[Christoph Hellwig]

On Thu, Mar 30, 2017 at 12:06:41PM +0200, Lars Ellenberg wrote:
> On Thu, Mar 23, 2017 at 10:33:40AM -0400, Christoph Hellwig wrote:
> > It seems like DRBD assumes its on the wire TRIM request always zeroes data.
> > Use that fact to implement REQ_OP_WRITE_ZEROES.
> > 
> > XXX: will need a careful audit from the drbd team!
> 
> Thanks, this one looks ok to me.

So the DRBD protocol requires the TRIM operation to always zero?

> The real question for me is, will the previous one (21/23)
> return != 0 (some EOPNOTSUPP or else) to DRBD in more situations than
> what we have now?

No, blkdev_issue_zeroout should never return -EOPNOTSUPP.

> Will it make an fstrim cause thinly provisioned
> devices to suddenly be fully allocated?

Not for SCSI devices.  Yes for dm-thinp until it implements
REQ_OP_WRITE_ZEROES, which will hopefully be soon.