libsed in mdadm

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

Hello,
IMSM/VROC is going to support self-encrypted drives. With this feature you need
to unlock the drives during boot-up in UEFI first. It is kind of protection
from physical stealing.

To ensure security, Linux have to respect that. It means that we need to
determine if the drive support locking and do not allow to mix locked and
unlocked drives in one IMSM array.

To grab that information we will need to impose the "magic commands" to the
drives. There is a libsed library, designed for such purposes:
https://github.com/sedcli/sedcli

So far I know, this library is not released under distributions (not handled by
package managers) and that will bring not user friendly dependency- you will
need to compile and install the lib first to build mdadm.

The sedcli project is maintained in Intel, currently it is not in active
development but there are no plans to drop it, interest around it is growing as
you can see. It seems to be great opportunity for this project to
become integrated with mainstream distributions when mdadm will start to
require it.

So, my questions are: Are we fine with adding this dependency? Are there big
cons you see?
Obviously, I will make it optional like libudev is.

I can try to re-implement the functionality I need in mdadm but it is like
reinventing the wheel.

Any feedback will be appreciated.
Mariusz