Re: [nfs-utils PATCH] systemd: add generators for the rpc_pipefs mountpoint

[Steve Dickson <SteveD@RedHat.com>]

On 03/29/2017 06:59 PM, Scott Mayhew wrote:
> On Wed, 29 Mar 2017, Steve Dickson wrote:
> 
>>
>>
>> On 03/29/2017 02:02 PM, Scott Mayhew wrote:
>>> On Wed, 29 Mar 2017, Steve Dickson wrote:
>>>
>>>> Hello,
>>>>
>>>> On 03/28/2017 09:37 AM, Scott Mayhew wrote:
>>>>> The nfs.conf and idmapd.conf files both have config options for the
>>>>> pipefs mountpoint.  Currently, changing these from the defaults also
>>>>> requires manually overriding the systemd unit files that are hard-coded
>>>>> to mount the filesystem on /var/lib/nfs/rpc_pipefs.
>>>> The Pipefs-Directory config variable is not documented in either
>>>> idmapd.conf(5) or rpc.idmapd(8) or nfsidmap(5) so the only way
>>>> to know about it as to read the code. I would not call that
>>>> a supported interface and can easily be removed. IMHO.
>>>> The same thing goes for the Cache-Expiration variable. 
>>>
>>> So you're saying to document the Pipefs-Directory and Cache-Expiration
>>> variables, not remove them... right?  I think they should be documented
>>> in idmapd.conf(5) since the other pages both refer to idmapd.conf(5).
>> I'm saying since they are not documented interfaces so we can
>> move them out of idmapd.conf and into nfs.conf
> 
> But what is gained by doing that, really?  And "not documented" is not
> quite the same thing as "unknown".  The RHEL 4 idmapd.conf used to even
> include the Pipefs-Directory parameter, and I see references to it in
> both Red Hat bugzillas and knowledge articles.
What is gained is we are starting to move all the 
server configurations to one file. This is upstream
so these changes are not going make a difference to
legacy OS.

Plus I'm guess nobody ever changed Pipefs-Directory config
because nobody knew what it did. It is a pretty low level
knob.
 
> 
>>>>
>>>>>
>>>>> This patch adds two generators to create drop-in config files to
>>>>> override the dependencies for the systemd units that require the pipefs.
>>>>> There are two because rpc.idmapd uses a separate configuration file.  If
>>>>> idmapd's configurations are ever folded into the nfs.conf, then the
>>>>> idmapd-rpc-pipefs-generator.c can be deleted and generate=1 can be
>>>>> specified for idmapd in rpc-pipefs-generator.c.
>>>> So I'm thinking we just read Pipefs-Directory out of 
>>>> one spot that would be /etc/nfs.conf.
>>>
>>> I agree but then rpc.idmapd and nfsidmap should be modified to read
>>> /etc/nfs.conf instead of /etc/idmapd.conf by default, but that could be
>>> confusing unless some of the section names and/or variable names from
>>> /etc/idmapd.conf were changed up a bit.  That's quite a bit more than
>>> I'm trying to accomplish here.
>> I'm not saying move them all just move Pipefs-Directory into /etc/nfs.conf.
>> Move them would be a pain and I agree, well beyond the cope of what you
>> are trying to do here.
>>
>> Yes, this means rpc.idmap would have to read out of two config files
>> but in time that could change and looking at the code reading
>> out of second config file does seems too difficult.
>>
> I'm not saying it would be difficult reading those two settings out of a
> different config file, I just don't see the need for it.
Again, to start the migration of all server knobs to move
to one config file. 

> 
> If you could specify the parameter once and only once, and have all the
> programs that use that parameter use the same value, then I think maybe
> it'd be a good idea, particularly for the pipefs filesystem where it
> probably doesn't make sense to have multiple filesystems mounted on
> different mountpoints...  but there's no support for 'global' settings
> in nfs.conf (maybe that's a good idea though).
Well in the nfs.conf man page "introduce a section called global". So
maybe now is the time to do that.

> 
>>
>>>
>>>> That way we would only 
>>>> have to support one of these generators.
>>>
>>> If your issue is that there are two generators then I can fold them into
>>> single one... then if the idmapd.conf ever get folded into nfs.conf it's
>>> simply a matter of deleting a few lines of code.  The only reason I made
>>> two generators is becuase it made more sense to me that way.  I'm fine
>>> either way.
>>>
>>>>
>>>> Also please document the Pipefs-Directory variable in both
>>>> the nfs.conf man page and in the example nfs.conf file
>>>> in the git tree. 
>>>
>>> It's actually already documented in both, under the gssd section.
>> Perfect... Just cut/past from the gssd section and add a 
>> idmapd section to the examples in nfs.conf showing the
>> default value.
>>
>>>
>>>>
>>>>>
>>>>> This patch also adds a unit file to mount the pipefs on /run/rpc_pipefs,
>>>>> since that is the most logical alternate location for the pipefs
>>>>> filesystem.  Users wanting to use some other location besides
>>>>> /var/lib/nfs/rpc_pipefs or /run/rpc_pipefs would have to create their
>>>>> own systemd mount unit file, but the generators would take care of the
>>>>> rest.
>>>> I'm not sure I understand why this new unit file, run-rpc_pipefs.mount,
>>>> is needed, especially since it is not being install (aka no updates
>>>> to the Makefile.am files).
>>>
>>> I forgot to update the Makefile.am by mistake.  I definitely want the
>>> new unit file.  The idea is to give users a choice between
>>> /var/lib/nfs/rpc_pipes and /run/rpc_pipefs without requiring them to go
>>> manually messing around with systemd configs.
>> Hmm... Why would users care and would a user do the switch via 
>> a systemd command?
> 
> Most users probably don't care.  But the pacemaker cluster resource
> agents do a bind mount over top of /var/lib/nfs.  In order to do that,
> they unmount the pipefs, do the bind mount, and then remount the pipefs.
> If unmounting the pipefs fails then the cluster has a tendency to fall
> apart.  By moving the pipefs out of /var/lib/nfs then that's one less
> thing to worry about.
For the HA world, moving the pipefs to /run makes thing much easier.
I get it... 

> 
> The way the switch is done is edit the nfs.conf and idmapd.conf and then
> either reboot, or do a 'systemctl daemon-reload' and then restart idmapd
> and gssd.
To me it seems more straightforward to change the all the daemons
to read from one file so only that file needs to be changed. 
 
> 
>> Also who is going to create that directory?
> 
> systemd creates the directory automatically.
>>
>> The point of all this is I don't think we needed two generator.
>> I would rather make changes to where (undocumented) config
>> knobs are read to avoid the second generator.
>  
> I've already boiled it down to one generator.  Does that make a
> difference?
I didn't know that... but still I would like to take any and all
opportunity to migrate things in one config file. 

steved.

> 
> -Scott
>>
>> steved.