Multi-threaded daemons such as dmeventd could benefit from some improvements to libdevmapper.
WONTFIX
i) We're moth balling libdevmapper with a view to replacing it's use with a re-engineered interface (probably dmexec, see https://github.com/jthornber/deconstructed-volume-manager/blob/master/examples/dm-exec/ex13.asm). ii) dmeventd should be changed to use the new ioctl that can wait for multiple events, rather than constantly polling the status of devices.