Re: mount default minor version behavior

[Steve Dickson <SteveD@redhat.com>]

On 11/11/2014 03:43 PM, Trond Myklebust wrote:
> On Tue, Nov 11, 2014 at 2:16 PM, Steve Dickson <SteveD@redhat.com> wrote:
>>
>>
>> On 11/11/2014 10:01 AM, Trond Myklebust wrote:
>>> One thing you should note when doing this: the current parser for
>>> /etc/nfsmount.conf does not support minor versions. I think it needs
>>> to, so that we can continue to use it to set defaults.
>> Well setting Nfsvers=4.1 will give you a v4.1 mounts (assuming
>> the server supports v4.1. but setting Defaultvers=4.1 does
>> give you a v4.0 mount, which will need to be fixed.
>>
>>>
>>> ...and to answer your questions above, I think that we should be able
>>> to specify a 'default nfsv4 minor version' in /etc/nfsmount.conf, and
>>> then negotiate down from there.
>>> IOW: extend the 'Defaultvers' and 'Nfsvers' options to support 4.0,
>>> 4.1, 4.2,....
>> Well Defaultvers is a negotiation with the server, Nfsvers is not.
>> So when Nfsvers set set there is no  negotiation, they get what is
>> set to (aka 3, 4, 4.0, 4.1, just like the command line).
>>
>> With  Defaultvers its a negotiation so set it to highest
>> version and let it go... I'm not sure we need another
>> variable to complicate things...
>>
>>>
>>> The result should be that If I do 'mount -t nfs' with no '-overs'
>>> option, then we start at 4.1 (if that is the default in
>>> /etc/nfsmount.conf) and then try 4.0, 3, 2 in that order.
>>> If I do 'mount -t nfs -overs=4', then again consult /etc/nfsmount.conf;
>>> - if there is a default matching a v4 minor version, then start at
>>> that and negotiate down (but stop at 4.0).
>> Again, I'm thinking this type of  complexity is not needed (especially
>> from a testing matrix point of view).
>>
>> besides, if someone is specifying a version on the command line, is most likely
>> they are not going to be using /etc/nfsmount.conf as all...
>>
>>> - if there is no default in /etc/nfsmount.conf, then perhaps assume a
>>> default of 0(????)
>> I'm thinking why not default to the better minor version?? 4.1 => 4.0 => 3
> 
> So at which minor version do you start? 4.10, 4.100?...
The highest one.... Set Defaultvers to the highest version
(including minor version) and then let the negotiations happen. 

> We don't want to have to recompile mount every time we add a new minor
> version in order to bump the maximum number, which is why I think we
> want to use /etc/nfsmount.conf and Defaultvers to define that (and
> assume '0' if undefined).
I agree. The fact that you can't set DefaultVers=4.2 and then 
negotiated down to what both sides support (even if its v3)
is a problem and needs to be fixed. 

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.

steved.