Re: [PATCH] null_blk: add zoned config support information

Bart Van Assche
2019-01-04T20:49:38Z

On Fri, 2019-01-04 at 15:37 -0500, John Pittman wrote:
> Thanks Bart; I made the changes and sent them in as a v2, I'm sure you
> already saw. I have a quick, unrelated question if you have a moment.
> In testing the null_blk driver, I found that trim commands sent by fio
> were rejected due to lack of support. Tracking down Shaohua's commit
> 306eb6b4a ("nullb: support discard"), he mentions that "discard makes
> sense for memory backed disk". Just to see what would happen, I
> edited the source to make discard a configurable parameter at
> modprobe, and after the edit & build, the trim commands submitted
> fine. Does this sort of change make sense? I mean the ability to do
> discard to null_blk without it being memory backed; solely for
> testing/benchmarking purposes. I haven't found any good instructions
> on creating a memory backed or discard enabled null_blk device from
> the command line, so I assume a higher level driver would have to hook
> in and enable these features manually. Thanks for your time and any
> information.

Hi John,

Jens as the block layer maintainer has the last word about this. Personally
I would welcome that functionality. Before discard functionality was removed
from the brd driver I used the brd driver to test the discard functionality
in storage target stacks. If discard functionality would be added to the
null_blk driver then that would make it possible to use that driver for
testing the discard functionality in e.g. LIO. See also commit f09a06a193d9
("brd: remove discard support").

I'm not sure that we need a modprobe parameter to enable or disable trim
functionality in the null_blk driver. I'm fine with always enabling trim
functionality in that driver.

Bart.