[dm-crypt] renaming of device

Ross Boylan ross at biostat.ucsf.edu
Sat Jan 16 01:30:11 CET 2010

On Fri, 2010-01-15 at 04:58 +0100, Arno Wagner wrote:
> Good idea, but no. Must be something in the udev configuration
> after all. Not that I found anything. Or anything in the logs.
> Hmm. Oh, well. It is not that important. But I really hate this
> badly documented obscure "automagical" stuff. As soon as anything
> breaks, it really sucks. 
> On the side of where cryptsetup finds the device for a specific
> major and minor number, it is indeed a simple recursive directory
> traversal. Unfortunately it is in libdevmapper.c, i.e. in the 
> system lib of that name. That means it cannot easily be changed.
I have a comment and a question.

The comment is that I think udev on Debian has some private place that
it stashes away mappings so that network cards (for sure) and disks (I
think) have stable names.  I think it's a Debian-specific feature,
though other distros may do something similar.

The question concerns the use of major:minor to identify devices.  I
thought the same physical device can have different major:minor on
different boots.*  Is that so, and if so, can it cause problems for
dm-crypt, such as causing it to pick the wrong underlying volume?

I'm pretty ignorant in this area so a) take what I say with a grain of
salt and b) I'd appreciate any wisdom.


Ross Boylan

*I think the Debian stuff stabilizes the relation between physical
devices and names like /dev/sdd, but not necessarily physical devices
and major:minor.

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