Re: Configuring fs_locations on Linux upstream server pseudo fs for session trunking

["bfields@fieldses.org" <bfields@fieldses.org>]

On Wed, May 25, 2016 at 05:29:35PM +0000, Adamson, Andy wrote:
> Anna Schumaker who reviewed my client side session trunking patchset, wants a full featured version of both the client and the server session trunking pieces before accepting the session trunking feature upstream. To that end, I want to implement the server mountd V4ROOT processing of an fs_locations configuration to satisfy an fs_locations request on the pseudo fs.
> 
> The forwarded message is from an email stream between Bruce, Chuck and I concerning the server pseufo fs fs_locations configuration that I’m now sharing with the list.
> 
> Some background:
> 
> The recent "NFSV4.1,2 session trunking” Version-5 patch set sent to the list notes (in patch 00/10):
> 
> The pseudo-fs GETATTR(fs_locations) probe session trunking
> was tested against a Linux server with a pseudo-fs
> export stanza (e.g. a stanza with the fsid=0 or fsid=root
> export option) and a replicas= export option
> (replicas=<path1>@<server1>:<path2>@<server2>..)
> Note that this configuration is for testing only. A future
> patchset will add the replicas= configuration to the
> NFSEXP_V4ROOT nfsd and mountd processing.
> 
> 
> There are several ideas on how to accomplish mountd/V4ROOT fs_locations configuration in the forwarded message. See inline.
> 
> 
> > Begin forwarded message:
> > 
> > From: Chuck Lever <chuck.lever@oracle.com>
> > Subject: Re: Configuring fs_locations on Linux upstream server
> > Date: May 6, 2016 at 4:31:00 PM EDT
> > To: "J. Bruce Fields" <bfields@fieldses.org>
> > Cc: "Adamson, Andy" <William.Adamson@netapp.com>
> > 
> > 
> >> On May 6, 2016, at 4:16 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >> 
> >> On Fri, May 06, 2016 at 02:20:12PM -0400, Chuck Lever wrote:
> >>> Seems like when a server does not return a list, that is
> >>> information the client can use: basically, there is no
> >>> ability to do any session trunking. It has to be set up
> >>> explicitly; is that a bad thing, operationally?
> >> 
> >> I like the idea of it being opt in on the server.
> >> 
> >> Suppose the server transparently starts advertising all available
> >> addresses for session trunking.  It's not hard to imagine cases where
> >> that would go wrong.  E.g., maybe the server has the odd wireless or
> >> 100Mb or other interface that happens to work but that's slow.  Then
> >> somebody upgrades their server and performance goes down and it may take
> >> them a while to figure out why.  Whereas if they'd had to opt in they'd
> >> probably have avoided advertising an inappropriate interface.  Or at
> >> least they'd have a better chance of figuring out that turning on
> >> trunking was what caused the problem.
> >> 
> >> I'd rather not force people to export "/" explicitly, though.  It's fine
> >> for testing, but:
> >> 
> >> 	- I don't think we give a way to do an explicit V4ROOT export,
> >> 	  so they'd be exposing their entire root partition.  We could
> >> 	  fix that, but
> >> 	- the pseudofs just seems to me like something people shouldn't
> >> 	  normally have to think about.  It's a protocol implementation
> >> 	  detail, I'd rather hide it.  It'd be to easy to configure it a
> >> 	  little wrong, I think.
> >> 
> >> We can still do this by adding a replicas= option to the / export, but
> >> we can let rpc.mountd do that internally instead of making the admin add
> >> it to /etc/exports.
> >> 
> >> But then you still need a way for the admin to tell rpc.mountd to cook
> >> up the replicas= option.....  I'm not sure what that should look like.
> 
> Idea 1: extra syntax in /etc/exports

It's not really export-specific information.  I wonder if it'd be better
to pass it on the rpc.nfsd commandline?

	rpc.nfsd --multipath-set="192.168.0.1,192.168.0.2"

(and then that can be configured in /etc/sysconfig/nfs or whatever)?

> >> Maybe some extra syntax in /etc/exports, but what do they need to give
> >> us--just one list of IP addresses?  Chuck, any ideas?
> 
> Idea 2: xattr attached to “/"
> 
> > 
> > How about using the same approach used for junctions:
> > put the list in an xattr attached to / ? mountd can
> > extract that when the kernel asks for help satisfying
> > a GETATTR(fs_locations) on V4ROOT.

I don't think that works.  "/" isn't a good place to put configuration.
It could be read-only, among other things.

> Idea 3: new /etc/ config file
> > 
> > Or it could be put in a separate config file in /etc.
> > You might want to specify more than just the i/f list
> > here; for instance, the security policy for the
> > pseudofs, or a constant fsid UUID, among other things.
> 
> 
> API to update the i/f list.  This is not about where to hold fs_locations config info, but rather how to insert the (changed) info into the running system.
> 
> > 
> > Also, I suggested to Andy earlier:
> > 
> >> I find myself leaning towards mechanisms that are easy
> >> both for admins and for programs (ie, an API). Perhaps
> >> one day you might want to add a command that updates the
> >> i/f list from the scripts in /etc/sysconfig/network-scripts,
> >> for instance.
> >> 
> >> As part of an ifup:
> >> 
> >> nfspfs add <addr>
> >> 
> >> and ifdown:
> >> 
> >> nfspfs remove <addr>
> >> 
> >> I wrote some Python code to manipulate entries in
> >> /etc/exports, now found in fedfs-utils. It's icky.
> > 
> > I think we should move away from "edit this file
> > and save it, then restart rpc.xyzpdq". Build some
> > command line interfaces for this.

I'm OK with that.

(Note do have that for information in /etc/exports--we have exportfs.
Is there a reason that didn't work for fedfs-utils?)

--b.

> > 
> > And as you have suggested many times: separate
> > policy from mechanism. /etc/exports is the
> > mechanism.
> > 
> > --
> > Chuck Lever
> 
> Bruce - do you have a preference between #1 and #2 or #3 (or another idea?)
> 
> Thanks
> 
> —>Andy