Re: mount default minor version behavior

[Steve Dickson <SteveD@redhat.com>]

On 11/12/2014 10:28 AM, Trond Myklebust wrote:
> On Wed, Nov 12, 2014 at 10:10 AM, Steve Dickson <SteveD@redhat.com> wrote:
>>
>>
>> On 11/12/2014 09:31 AM, Trond Myklebust wrote:
>>>> My point is I don't think we need another variable, say
>>>>> DefaultMinVers, that defines the minor version of v4. I'm
>>>>> thinking that's its overkill and adds unnecessary complexity.
>>>>>
>>> I never said we do.
>> Ok... I misunderstood...
>>
>>>
>>> I think we're in agreement mostly; the only point where I see
>>> disagreement is when Defaultvers is unset.
>>> My position is that in that situation, we don't know what starting
>>> point to use for minor version negotiation, and so we should just
>>> default to minor version 0: if the sysadmin want a different default,
>>> then the answer is to set Defaultvers...
>> Gotta... and there is a disagreement... I saying we make the
>> default the highest supported minor version. With the
>> Linux client and server that's v4.2. So when no option is
>> given and Defaultvers is not set, try 4.2, then 4.1 and
>> then 4.0 and finally v3.
> 
> Only for Linux 3.11 and newer, and only if they enable CONFIG_NFS_V4_2
> / CONFIG_NFSD_V4_SECURITY_LABEL.
Being dynamic is never easy! ;-) 

The server has /proc/fs/nfsd/versions file that defines the
supported versions. Maybe we can come up with something 
on the client that would tell what protocols are supported...

> 
> Unless we want to have different defaults for older kernels, this sort
> of implies that we're moving in the direction of coupling the
> nfs-utils releases more tightly to the kernel version. I'm neutral to
> that, but I do want to call it out.
> 
>> But I do see your point of not having to recompile mount
>> when we want to change the default minor release so
>> how that default is set is the question... Maybe
>> an environment variable??
> 
> That's still something that requires a user or sysadmin action, and it
> wouldn't really play well with autofs and its ilk. As Marie Antoinette
> would say: "Let them edit /etc/nfsmount.conf"
Clever.. :-) 

> 
>> One down side of being the aggressive with minor version
>> negotiation is legacy servers (aka AIX). Today we
>> don't negotiate well with those types of servers...
>> Its not our fault, but is a problem...
> 
> Is this because they don't implement that part of RFC3530?
The server returns the wrong type of error when a v4
mount is done so the mount fails instead of rolling back
to v3.

steved.