Thanks Bart, I appreciate it.
On Fri, Jan 4, 2019 at 3:49 PM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>
> 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.
