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

[Chuck Lever <chuck.lever@oracle.com>]

> On May 25, 2016, at 2:48 PM, bfields@fieldses.org wrote:
> 
> 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?)

To make changes that can survive a server reboot,
you have to update /etc/exports.


> --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
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--
Chuck Lever