On Sun, Mar 25 2012 at 7:54pm -0400, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Sun, Mar 25 2012 at 6:46pm -0400, > Amar Mudrankit <amar.mudrankit@xxxxxxxxx> wrote: > > > Hi all, > > > > I am building an experimental device mapper target which is supposed to > > receive > > all TRIM requests (REQ_DISCARD). Irrespective of whether underlying actual > > physical block device supports discards or not, my device mapper target > > should > > receive REQ_DISCARD bios. > > I'm just curious but: what will your target do in general? > > > In my target, I set: > > > > ti->num_discard_requests = 1; > > ti->discards_supported = 1; > > You'll also want to set ti->discards_supported > > see: http://git.kernel.org/linus/4c259327 ah, I now see you already did set discards_supported. > > So, if my device mapper target does not implement iterate_devices function > > (used to set max_discard_sectors based on underlying physical device's > > discard > > support) or underlying physical device does not support discards, then there > > is no way for device mapper target to set max_discard_sectors more than 0 > > to receive REQ_DISCARD commands. > > > > Is this analysis correct? Or I am missing something? > > All DM targets should implement .iterate_devices -- intent is to iterate > over all data devices. > > You'll also want to implement .io_hints to set limits->max_discard_sectors > (like drivers/md/dm-thin.c does). BTW, the dm-thin.c discard changes will be merged in 3.4, you can see the relevant patches here: http://people.redhat.com/agk/patches/linux/editing/dm-thin-support-discards.patch http://people.redhat.com/agk/patches/linux/editing/dm_thin-add-pool-target-flags-to-control-discard.patch -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
