On Tue, Oct 04, 2016 at 04:39:28PM -0700, Andy Grover wrote: > devicemapper is using uevents for: > a. dm-verity detected corruption > b. dm-multipath: path failed or reinstated > c. dm device renamed > d. there's also some use in md and bcache. > > devicemapper uses DM_EVENT ioctl (yuck) for: > 1. dm-thin pool data/metadata filling up (hit a threshold) > 2. dm-cache is now clean > 3. dm-log flushed or log failed > 4. dm-raid error detected or sync complete > there doesn't seem to be much technical differentiation between the > two lists. The distinction in dm is that events in the first category may affect the availability of the device: they represent major (and hopefully rare) changes. Events in the second category are just notifications: no impact on /dev, no need to trigger udev rules, and their use will continue to be extended, and (rarely at the moment) could be frequent (which is no problem for the existing polling-based mechanism). > Instead of using uevent for everything, we could go to a separate > genetlink for 1-4 instead of making them use uevent like a-d, but we'd > end up with two different userspace notification techniques. We see these as two different categories of notifications, and prefer the greater flexibility a mechanism independent of uevents would provide. The team has discussed several alternatives over the years but didn't make a decision as we've not yet reached a point where we're straining the existing mechanism too far. Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
