Re: [dm-devel] [PATCH v2 0/3] Fix dm-crypt zoned block device support

[Mikulas Patocka <mpatocka@redhat.com>]

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

> > 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.
> 
> > 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


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