Re: [nfs-utils PATCH] retry on EPERM from NFSv4 mount attempt

[Neil Brown <neilb@suse.de>]

On Tue, 24 Nov 2009 15:56:16 -0500
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> On Tue, Nov 24, 2009 at 09:29:47AM -0500, Steve Dickson wrote:
> > >  So I think we need to fall back on EPERM as well.  See below.
> > I already posted this patch on the v4 mailing list
> > http://linux-nfs.org/pipermail/nfsv4/2009-November/011595.html
> > but it got shot down...  at least that's how I interpreted the
> > responses... 

Thanks for the reference ... clearly I am not keeping up with my
nfs mailing lists....


> > 
> > But I do thing we need this, since there are so many server 
> > that will simple break if we don't... Agreed?

Agreed that we certainly need something.  We cannot expect people to
reconfigure their servers because they installed new software on the
client.

> 
> My position is that servers should either a) turn off NFSv4 or b) add
> a pseudoroot, and that we should modify initscripts to make this
> harder to screw up.

In the ideal world, yes.  Maybe this is best done in the kernel?
Can we synthesis an RPC-protocol-not-supported error if and NFSv4
request arrives from a client for which no pseudo-root is configured?

> 
> (For now (without automatic pseudoroot creation) we should by default
> be running rpc.nfsd with -N 4; and adding the v4 support should be
> something administrators do when they add a pseudoroot.)

Hind sight is 20/20 they say.  We probably should have done this, but
I think it is now too late to do anything useful in the init scripts.

> 
> ((If this is really totally unfeasible, then I should quickly cue up a
> revert for the patch I have queued for 2.6.33 which changes this error
> again, to SERVERFAULT....))

Maybe - maybe not.

The situation on the client is that for a command that has
traditionally always performed a v3 or (before that) a v2 mount, we are
now trying a v4 mount.
I see that v4 attempt as opportunistic.  If anything goes wrong I think
it is reasonable to go back to "the old way".

So I think this piece of code in mount.nfs should retry on any error at
all, so it would not matter whether you change again to SERVERFAULT.

But I think the best fix for the kernel is to get nfsd4_proc_compound
to return RPC_PROG_MISMATCH if there is no pseudo root, and then get
svc_process_common to handle this and fake up appropriate min/max
version numbers.

Thanks,
NeilBrown