Re: [PATCH/RFC nfs-utils] nfsdcltrack: read configuration from a file

[Jeff Layton <jlayton@redhat.com>]

On Fri, 2016-11-11 at 09:17 +1100, NeilBrown wrote:
> On Fri, Nov 11 2016, Jeff Layton wrote:
> 
> > 
> > On Thu, 2016-11-10 at 15:58 +1100, NeilBrown wrote:
> > > 
> > > As nfsdcltrack is normally run directly from the kernel
> > > there is no opportunity to change the default
> > > storage directory.  This can be useful in a cluster to
> > > locate the "storage directory" on shared storage.
> > > 
> > > The easiest alternative is to allow configuration to be read from a
> > > file, particularly as nfs-utils already has code for parsing a config file.
> > > 
> > > So read the config file "/etc/nfs.conf" (or as set by ./configure) and
> > > look for "storagedir" and "debug" in the "nfsdcltrack" section.
> > > These values can still be over-ridden by command line options.
> > > 
> > > A generic name (nfs.conf) was changes for the config file so that
> > > other daemons can be enhanced to read configuration from there.
> > > This may be easier than passing command line arguments through systemd.
> > > 
> > I like the basic idea, but I'm not so sure we want to use a generic
> > config file like this. What else do you envision using this file?
> 
> See https://lwn.net/Articles/584373/ and surrounds (included where I
> said that I wouldn't be providing patches:-).
> 
> I'm not happy with current mechanisms for passing configuration from a
> configurator gui, through systemd, to various daemons.  Having a common
> config file, rather having to stitch together command-line args, feels
> like it might be a step in the right direction.  Given that I was adding
> a config file, I thought that leaving it open-ended might be a good
> idea.
> 
> We already have /etc/nfsmount.conf and /etc/idmapd.conf.
> How many more do we want?
> I note that that idmapd.conf contains Pipefs-Directory.  Various
> other daemons need to know where that is.  Wouldn't it be nice if they
> all read the one config file?
> 
> I haven't resolved in my mind where the "impedance matching" should
> happen.  To explain:
> Different distros put their configuration in different places
> (/etc/sysconfig/nfs /etc/defaults/nfs) and use different names for the
> same value.  These files are all "name=val" files, without the [section]
> headings of conf files.
> What is the best way to get the config from there to the local variables
> inside the various programs?
> 
> Currently a systemd service runs a script which reads the configuration
> file and writes out an environment file for systemd to read, which
> provides command-line args for each daemon.  I'd rather something more
> direct.
> 
> If the parsing of /etc/nfs.conf allowed
>   name=$var
> to extract 'var' from the environment, then (almost) each distro
> could have a static /etc/nfs.conf which listed which configuration
> variables affected which settings.  Then systemd could read the
> original configuration file to set up the environment, then each tool
> would read /etc/nfs.conf to extract the desired parts of the environment.
> 
> Except that wouldn't work for nfsdcltrack as we cannot easily control
> it's environment.  And there would probably be other things that didn't
> quite work right.

That could be remedied though it would take code changes in nfsdcltrack.

> 
> Maybe the best thing is for the configurator-gui to be required to run
> some post-processing thing which creates /etc/nfs.conf.
> Then of course, it could just create systemd drop-in files which
> created all the required arguments - then tells systemd to re-read those
> files.  So maybe this is only useful for programs that aren't run via
> systemd.
> 
> I'm as yet far from certain as to what I want, but keeping things
> extensible seems like a generally good principle.
> 

Agreed.

> > 
> > 
> > That said, if we are going to do this, we should probably make it clear
> > that it's for server-side configuration. Maybe "nfsd.conf" or
> > "nfs-server.conf" would be a better name?
> 
> Why only server-side?  rpc-gssd needs configuration too.  It and
> svcgssd (where used) are needed on both server and client (for
> NFSv4.0).
> 

I was thinking that we already had nfsmount.conf, so making this about
server-side configuration would be more intuitive for users. You do have
a good point about rpc.gssd though.

Regardless, I do applaud the idea making the setup of NFS clients and
servers less "fiddly". Once you get beyond a very basic setup,
administering NFS as a service (client or server) is rather difficult
today.

Transitioning to a more unified configuration scheme seems like it would
be good. Maybe we could even come up with a way to subsume nfsmount.conf
as well?

-- 
Jeff Layton <jlayton@redhat.com>