[CTDB] LMASTER/DMASTER implementation

[tridge at samba.org]

Alexander,

 > We started to implement LMASTER/DMASTER exchange logic in
 > http://samba.org/~ab/ctdb/

thanks, though I think the first thing we need to do to start adding
LMASTER/DMASTER logic is add the augmented header to the ltdb
records. We can't do anything sensible with LMASTER != DMASTER till we
have a place to store the location of the current DMASTER along with
the record data.

I'd suggest we need to start expanding common/ctdb_ltdb.c, and put all
the logic for dealing with the ltdb there, exposing functions for
asking for record, split into the user data and the ctdb header.

I'll be working from the spec in the "Extended Data Records" section
in the wiki. Once that's done, then I think doing the redirect will be
pretty natural in the code.

I'll probably also remove the TDB_INTERNAL flag and start using a real
tdb, but auto-generate the tdb name based on the vnn so that they
don't conflict when running all in the same directory on loopback.

Meanwhile, I'm hoping Peter might be able to make some progress at
getting the current prototype working with infiniband. The transport
layer stuff hopefully won't be changing much as we develop the higher
levels of the protocol (unless we hit a snag!).

Jim, have you started looking at the test suite? I think enough of the
API is there that you could start writing tests. They'll have to
change a lot as things develop, but it would be useful to have more
extensive tests available now.

Cheers, Tridge