On Mon, 19 Apr 2021, Damien Le Moal wrote:

quoted

I would say that it is incompatible with all dm targets - even the linear 
target is changing the sector number and so it may redirect the write 
outside of the range specified in dm-table and cause corruption.

DM remapping of BIO sectors is zone compatible because target entries must be
zone aligned. In the case of zone append, the BIO sector always point to the
start sector of the target zone. DM sector remapping will remap that to another
zone start as all zones are the same size. No issue here. We extensively use
dm-linear for various test environment to reduce the size of the device tested
(to speed up tests). I am confident there are no problems there.

quoted

Instead of complicating device mapper with imperfect support, I would just 
disable REQ_OP_ZONE_APPEND on device mapper at all.

That was my initial approach, but for dm-crypt only since other targets that
support zoned devices are fine. However, this breaks zoned block device
requirement that zone append be supported so that users are presented with a
uniform interface for different devices. So while simple to do, disabling zone
append is far from ideal.

So, we could enable it for the linear target and disable for all other 
targets?

I talked with Milan about it and he doesn't want to add more bloat to the 
crypt target. I agree with him.

Mikulas