On Fri, 2019-01-04 at 15:37 -0500, John Pittman wrote: +AD4 Thanks Bart+ADs I made the changes and sent them in as a v2, I'm sure you +AD4 already saw. I have a quick, unrelated question if you have a moment. +AD4 In testing the null+AF8-blk driver, I found that trim commands sent by fio +AD4 were rejected due to lack of support. Tracking down Shaohua's commit +AD4 306eb6b4a (+ACI-nullb: support discard+ACI), he mentions that +ACI-discard makes +AD4 sense for memory backed disk+ACI. Just to see what would happen, I +AD4 edited the source to make discard a configurable parameter at +AD4 modprobe, and after the edit +ACY build, the trim commands submitted +AD4 fine. Does this sort of change make sense? I mean the ability to do +AD4 discard to null+AF8-blk without it being memory backed+ADs solely for +AD4 testing/benchmarking purposes. I haven't found any good instructions +AD4 on creating a memory backed or discard enabled null+AF8-blk device from +AD4 the command line, so I assume a higher level driver would have to hook +AD4 in and enable these features manually. Thanks for your time and any +AD4 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+AF8-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 (+ACI-brd: remove discard support+ACI). I'm not sure that we need a modprobe parameter to enable or disable trim functionality in the null+AF8-blk driver. I'm fine with always enabling trim functionality in that driver. Bart.
