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

[Alasdair G Kergon]

On Sun, Jan 14, 2007 at 11:08:53PM +0100, David Härdeman wrote:
> 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.

http://lkml.org/lkml/2006/9/14/305

> 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
 
Sort of, but that page is incomplete and misses some important subtleties.
Userspace udev will *only* act on the KOBJ_CHANGE events.
(Add events will continue to be ignored.)
Udev will notify libdevmapper as the last thing it does.

Alasdair
-- 
agk at redhat.com