Re: [dm-crypt] renaming of device

[Arno Wagner <arno@wagner.name>]

On Sun, Jan 10, 2010 at 09:33:13PM +0100, Milan Broz wrote:
> On 01/10/2010 08:49 PM, Arno Wagner wrote:
> > Just found out why I did not notice this before:
> > When the disk is not present at mount time, the 
> > respective entry is not created in /dev/scsi/
> > and you get the traditional output. I think
> > "status" should always give the traditional one 
> > as it has a fixed mapping between major/minor and 
> > device (see Documentation/devices.txt in the 
> > Linux sources), while the /dev/scsi/ entry has not.
> 
> Cryptsetup simple tries to map major:minor number back
> to device name in /dev.
> (device-mapper know only major:minor pair - see dmsetup table)
> 
> The algorithm is very simple (and was probably written before
> udev was used so these special links in /dev did not exist).

Ah, so it probably goes recursively and finds the entries
in /dev/scsi before /dev/sd<somthing>, because c comes
before d in lexicographic order.
 
> So it need to add some preferred names and not print the first entry.

Indeed. The mapping to the traditional names is static.
I can write a bit of code for it and contribute that.

> Please can you add an issue to project pages to not forget about this?
> Probably good idea to fix it in next minor release.

Done.

> p.s. while the major:minor pair is fixed to device name,
> device name is not fixed to real disk drive.
> You can add some hw, or initialise modules in different order
> and disk name changes e.g. from /dev/sdb to /dev/sdd.

I know.
 
> Usually it is better use UUID instead of device name and use blkid
> to search for device (blkid supports LUKS header).

Agreed. The issue I have is when I do manual mappings and then
want to check what I did. The problem is the the traditional
names are not directly clear from the udev scsi names.

Arno

-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
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