Bug#403687: [david@hardeman.nu: Re: Bug #406697 - Device nodes are not removed when devices are brought down]

[David Härdeman]

I'll forward the same message to this bug that I forwarded to #406697 
(which is now closed). Feel free to substitute "cryptsetup" for 
lvm or any other suitable packages in the text below...

...

udev currently receives uevents from the kernel when a new device-mapper 
device mapping is created and creates a /dev/dm-* node. libdevmapper 
knows when devices are created/removed and creates the /dev/mapper/* 
nodes.

However, the kernel will not (AFAIK) send uevents when device-mapper 
mappings are renamed, changed or removed, so udev is not able to remove 
the devices when appropriate.

So the "fix" would be to add support for those uevents to the kernel 
and to change udev to act on them. Ideally it would create the /dev/dm-* 
devices and symlinks in /dev/mapper/*. 

Once that is in place, node creation can be removed from libdevmapper 
(meaning it will have to wait for the nodes to magically appear 
instead).

There is a writeup on this with some more details at:
https://wiki.ubuntu.com/UdevDeviceMapper

However, I can't see that anything needs to be done in cryptsetup 
(except making sure that all works when/if this behaviour is changed in 
libdevmapper).

-- 
David Härdeman