[PATCH] udevdb prototype

[PATCH] udevdb prototype

Here's an "idea" of what I had in mind for udevdb. Let me preface the
code with a few remarks:

1) I was expecting to write this udevdb for udev to keep track of
devices. I was planning an external package that depends upon udev
to provide an external API to the udevdb database. The calls for the
interface would be read only access. Not sure how you want to do
packaging, if having a separate package is ok or having it included
in udev.

2) I created it as it is because udev isn't a daemon. So, the open
database call doesn't take any parameters. My plan was to create a
udevdb_init function that took arguments for initializing the db
to start, where you could specify in memory only or a file location.
This can all be filled in.

3) I hacked the Makefile to get it to work. Not sure how you'd want
that in the future.

4) This assumes TDB has been installed elsewhere, you would need to
edit your Makefile and point it to the header and library locations.
How do you want to do TDB in udev? Do you want to just reference it
and make udev dependent on that package being installed. Or should
we do what samba does and include a limited tdb version in udev?

5) Again, I hacked udev into your existing code. In the future, I'd
probably make a function around the filling out the udevice before
calling the store command. Didn't know if you wanted to change
your add device function to use struct udevice rather than having
everything separate.

6) Not sure what we should include in the udevice structure that's stored
by udev. I made a stab at a first shot - we can add and remove of course,
this was a first pass. I've come to realize - with you including libsysfs
in udev, the "external" interface that references udevdb could make
use of getting information from through libsysfs from sysfs and doesn't
need to be in udevdb.

7) I could write a namedevdb for namedev's device management if you
wanted.