The udev conundrum (1)

• In response to the ADD event, some of the udev rules may attempt to open the devices to look for signatures.

• • Device-mapper devices initially have no table and are empty, so whether or not a signature is found depends on whether the rule is processed before or after the subsequent load and resume operations – a race.
  • LVM2 makes use of short-lived devices – e.g. create, wipe, destroy. But if a udev rule opens the device, it might still be open when LVM2 attempts to destroy it – the DM_DEV_REMOVE ioctl might fail.