[PATCH] CTDB recovery lock with arbitrary cluster mutex

[Martin Schwenke]

On Wed, 27 Apr 2016 07:47:16 +0200, Ralph Boehme <slow at samba.org> wrote:

> On Tue, Apr 26, 2016 at 01:45:40PM +1000, Martin Schwenke wrote:
> > [Resending from correct address...can moderators please drop the other one?]
> > 
> > The attached patch set changes the CTDB recovery lock so that it can be
> > implemented using an arbitrary, external cluster mutex helper.  At the
> > configuration level this looks like:
> > 
> >   CTDB_RECOVERY_LOCK="!/path/to/my/cluster/mutex/helper [arg ...]"
> > 
> > Without the leading '!' CTDB continues to use the setting as the name
> > of a recovery lock file, which is passes to the provided fcntl(2) lock
> > helper.  
> 
> would it make sense to use a scheme similar to KRB5CCNAME? Eg
> 
> CTDB_RECOVERY_LOCK="/path/to/file"
> CTDB_RECOVERY_LOCK="FILE:/path/to/file"
> CTDB_RECOVERY_LOCK="EXTERNAL:/path/to/external_program"

We do that for CTDB_LOGGING, where we have 2 very different options...
and the possibility of others in future.

However, in this case I'm not not sure the extra verbosity would add
anything.  I don't think the 2nd option of "FILE:" makes sense because
it means there would be 2 ways of saying the same thing.  I really
want to continue to allow a bare filename to be specified, partly
because it is backward compatible and because I think that most people
will use the default helper in the medium term.

If I thought this was likely to be extended beyond the choice
between the default and an arbitrary command string, then I think that a
more general syntax would be useful.  At the moment I'm leaning towards
brevity.

If there are strong opinions then I'm happy to be convinced.  The code
change would be small and the documentation is easy to update.

peace & happiness,
martin