[dm-crypt] renaming of device

Milan Broz mbroz at redhat.com
Sat Jan 16 09:39:58 CET 2010


On 01/16/2010 03:46 AM, Arno Wagner wrote:
> It does. Each possible /dev/sd<x> has a defined, fixed 
> major/minor, see Documentation/devices.txt in a Linux kernel 
> source tree.

so long thread:-)

Well, the situation is more complicated.

If cryptsetup uses only "real" block devices (like /dev/sdaX),
then fix to display proper device is is trivial.
(Parsing is in cryptsetup internal, not system libdevmapper currently.)

But if you have stacked devices "virtual block devices"
(crypt over MD or over LVM) it can be different - you want to see
/dev/VG/LV as device, not /dev/dm-X.

(btw dm-X names are not persistent and were intended to be kernel internal
only, unfortunately now are visible in userspace because of unified
udev event processing. And renaming these nodes to me more user-frientdly
in kernel is not easy because of various name length limits and different
approach for renaming of active DM devices) 

But the real problem now is that device-mapper library is just
in process of transition to udev (all nodes and symlinks will be created
by udev and not internally in libdevmapper).
And this changed (unified) some nodes to symlinks and vice versa.

With various maintainer's udev rules in various ditributions it creates nice
mix and Debian usually modifies even default rules for dm devices.

(Actually if you have an udev rule, which creates another node and not
symlink in /dev/scsi/..., it is  probably not correct, it should be symlink.)

Anyway, I'll plan to fix it somehow in next minor release of cryptsetup
(1.1.1 probably).

Milan


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