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Bug#403687 lvm2: several issues with devmapper devices

Steve asked today:
<vorlon> fjp: I'm confused why bug #403687 is marked as RC, instead of bug 

I've decided to answer by mail instead of on IRC because this issue 
probably needs some coordination between maintainers of several packages.

It looks certain that #402511, and probably also #401393 were introduced 
by this change in udev (0.103-1):
* udev.rules, devfs.rules: stop suppressing creation of dm-* devices,
  because they are needed by HAL. (Closes: #392623)

The second line in this snippet from /etc/udev/udev.rules was dropped:
# device mapper creates its own device nodes, so ignore these
KERNEL=="dm-[0-9]*",            NAME=""
KERNEL=="device-mapper",        NAME="mapper/control"

The reason I filed #402511 as important is because, although it is a clear 
regression and IMHO rather ugly, it is still mostly a cosmetic issue.
It looks like vgchange just loops over all /dev/dm-* devices and checks if 
any of them are LVM volumes, and prints an error if a device does not 

My conclusion is that udev now creates /dev/dm-* device nodes for cryto 
devices (and possibly other dm devices too), but nothing yet takes 
responsibility for _deleting_ them when the corresponding crypto devices 
are brought down [1]. This looks like a structural issue, but I have no 
idea if that should be the responsibility of the device mapper, udev or 
I also wonder what the risk is of other, not yet reported, issues 
introduced by the change in udev.

The reason I filed #403687 as RC is because IMO it is the _combination_ of 
several issues introduced by the change in udev that needs to be looked 
at before the release. I have no idea how important the HAL-support is, 
but the regressions it introduced seem serious enough to consider 
revering it.
IMO the management of /dev/dm-* devices is something that needs to be 
looked into structurally by maintainers of _all_ involved packages 
(probably also dmraid), I'll leave it to others whether that needs to be 
done before or after the release.


[1] The crypto devices in /dev/mapper/ *are* correctly removed after
S48cryptdisks has run, but the corresponding /dev/dm-* devices are not.

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