Re: [PATCH] dm-delay: support zoned devices

[Christoph Hellwig <hch@lst.de>]

On Fri, Mar 21, 2025 at 01:52:41PM -0400, Benjamin Marzinski wrote:
> On Fri, Mar 21, 2025 at 08:18:16AM +0100, Christoph Hellwig wrote:
> > Add support for zoned device by passing through report_zoned to the
> > underlying read device.
> > 
> > This is required to make enable xfstests xfs/311 on zoned devices.
> 
> On suspend, delay_presuspend() stops delaying and it doesn't guarantee
> that new bios coming in will always be submitted after the delayed bios
> it is flushing. That can mess things up for zoned devices. I didn't
> check if that matters for the specific test. Setting
> 
> ti->emulate_zone_append = true;
> 
> would enforce write ordering, at the expense of adding a whole other
> layer of delays to zoned dm-delay devices. Since this isn't really
> useful outside of testing, I think that could be acceptable if necessary
> (it would require us to support table reloads of zoned devices with
> emulated zone append, since tests often want to change the delay).
> However it would probably be better to see if we can just make dm-delay
> preserve write ordering during a suspend.

My use case is all about using zone append, so emulating it would be
a bit counter productive, but I'll give it a spin.  I doubt that this
test is very timing critical.