Dm-crypt, device-mapper and sysfs

From: W. Michael Petullo
Date: Tue Nov 02 2004 - 00:41:48 EST

I am interested in allowing the Hardware Abstraction Layer (HAL) to
interface with dm-crypt devices. I would like to see hald have the
ability to automatically mount removable encrypted drives when they are
plugged in.

I have a working prototype of this idea except for one issue.
Currently, dm-crypt registers its managed devices in the kernel's
sysfs. This is good. However, unlike most of the devices in
/sys, dm-crypt devices don't have a link named device. For most
devices, this link specifies the bus the device is connected to.
On my iBook, for example, /sys/block/hda/device points to
/sys/devices/pci0002:02/0002:02:0d.0/ide0/0.0. This is my IDE bus.

Hald expects to find a link like this when it is building its device tree.

I've discussed this issue on the dm-crypt mailing list and Christophe
thinks this is a more general device-mapper issue. So I don't put words
in his mouth, here is what he said:

> dm-crypt is a device-mapper target, it doesn't do any sysfs interaction.
> There were some plans, even patches, to export more device-mapper
> functionality into sysfs. Besides, a mapped device can consist of
> several other devices and different targets. cryptsetup has the ability
> to query an existing device, it will tell you if it is a "valid
> cryptsetup'ed device". Also there a are plans to put some metadata into
> the first blocks of the device so that it can be automatically
> recognized as encrypted device.

So my question is this:

Should the device-mapper driver be modified to provide a device link?
If so, what should it point to?


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