Re: [PATCH] nfsd: allow SCSI layout support without Block layout

From: "J. Bruce Fields" <bfields@fieldses.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Benjamin Coddington <bcodding@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	xfs@oss.sgi.com
Subject: Re: [PATCH] nfsd: allow SCSI layout support without Block layout
Date: Wed, 6 Jul 2016 18:41:41 -0400	[thread overview]
Message-ID: <20160706224141.GA21982@fieldses.org> (raw)
In-Reply-To: <20160706221648.GE12670@dastard>

On Thu, Jul 07, 2016 at 08:16:48AM +1000, Dave Chinner wrote:
> On Wed, Jul 06, 2016 at 08:43:26AM -0400, J. Bruce Fields wrote:
> > On Wed, Jul 06, 2016 at 05:58:09AM -0400, Benjamin Coddington wrote:
> > > On 6 Jul 2016, at 5:19, Dave Chinner wrote:
> > > 
> > > >On Tue, Jul 05, 2016 at 09:48:47PM -0400, Benjamin Coddington wrote:
> > > >>We shouldn't have to configure both NFSD_BLOCKLAYOUT and
> > > >>NFSD_SCSILAYOUT if
> > > >>all we want are SCSI layouts on the server, so define the xfs export
> > > >>operations for either configuration.
> > > >>
> > > >>Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> > > >
> > > >I don't really like exploding config option dependencies into
> > > >subsystems that aren't actually related to the config options.
> > > >It's confusing enough laready that we've got XFS code dependent on
> > > >PNFSD config options without adding more to it. Instead, I'd
> > > >suggest this should be resolved in the kconfig files. i.e. make
> > > >CONFIG_NFSD_SCSILAYOUT=y select CONFIG_NFSD_BLOCKLAYOUT to resolve
> > > >the config dependency at config time.
> > > 
> > > But the point is to leave CONFIG_NFSD_BLOCKLAYOUT undefined
> > > otherwise knfsd
> > > will advertise block layouts to clients -- which we don't want.
> 
> Pnfsd layout is determined at compile time?

On the server side it's currently controlled just by that and by a
single off-or-on "pnfs" option.  Well, and client behavior also
determines which one's actually negotiated in practice.

> That's seems less than useful to me for distros wanting to support for
> multiple layout types in the one kernel. i.e. Shouldn't the layout to
> be advertised be something like a per-export configuration option
> rather than determined at compile time define?

Yes, eventually we'll want something like that.  For now it's not
terribly interesting.

> > > Would a third define specific for xfs_export_operations that gets
> > > set in kconfig files work for you?  Something like XFS_PNFS_EXPORT_OPS.
> >
> > That makes sense to me....
> 
> Sounds good, but I'd drop the "XFS_" prefix because when multiple
> filesytems end up supporting it, we don't want to have to select
> every single one of them from the PNFSD config options...

OK.

--b.

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