This is a demo/test program for a proposed dm event mechanism using poll().

Steps:

• Build and boot a kernel with the poll DM event patches
• install device-mapper-devel.
• compile this program with make
• Set up some dm devices that might generate an event, such as a thin LV on a massively-underprovisioned thinpool
• run this
• start using the thin LV, it should generate a low-water event, and this should tell you that and print its status