Re: [PATCH 2/2] Enable v4 mounts when either "nfsvers=4" or "vers=4" option are set (vers-02)

[Steve Dickson <SteveD@redhat.com>]

On 08/25/2009 03:32 PM, Chuck Lever wrote:
> On Aug 25, 2009, at 3:18 PM, Steve Dickson wrote:
>> On 08/25/2009 02:59 PM, Chuck Lever wrote:
>>> On Aug 25, 2009, at 1:55 PM, Steve Dickson wrote:
>>>> commit 1471d23d692efc7388794a8a3c3b9e548d1c5be8
>>>> Author: Steve Dickson <steved@redhat.com>
>>>> Date:   Tue Aug 25 12:15:18 2009 -0400
>>>>
>>>>   Make sure umount use correct fs type.
>>>>
>>>>   umounts use the fs type in /etc/mtab to determine
>>>>   which file system is being unmounted. The mtab
>>>>   entry is create during the mount. To ensure the
>>>>   correct entry is create when the fs type changes
>>>>   due to the mount options, the address of the fs_type
>>>>   variable has to be passed so it can be updated.
>>>
>>> In general, my policy is to record the user requested mount options in
>>> /etc/mtab, and let umount.nfs handle renegotiating as needed.  For
>>> version/transport this means that the server's configuration can change
>>> between the mount and the umount, and the umount will still work.
>>>
>>> Perhaps this is not a consideration for NFSv4, but leaving the mount
>>> options as specified by the user would save the need to update the fs
>>> type, and would be a consistent policy for v2, v3, and v4.  I think it
>>> would be cleaner to teach umount.nfs to do the right thing with "-t nfs
>>> -o v4" rather than rewriting the options in /etc/mtab.
>> Since nfs4 is truly a separate/different file system from nfs in the
>> kernel, I think we should continue making that distinction in system
>> files like mtab and /proc/mounts....
> 
> We are teaching mount.nfs not to care about nfs/nfs4 (at least
> externally).  Why should umount.nfs?
That's not quite accurate... IMHO.. I see it as we are teach mount.nfs to
accept new command line arguments that will cause a nfs4 file system
to be mounted... and that is done by caring which fs type mount is
dealing with... 

> 
>> Also note there is no '-o ' flag to umount so 'umount -t nfs -o v4' is
>> not valid... but 'umount -t nfs' is and works on both nfs4 and nfs
>> file systems.
> 
> Sorry I wasn't clear.  I meant that umount.nfs should be able to read a
> line in /etc/mtab that has "nfs" and "v4" and do the right thing... then
> you wouldn't have to change the fs_type in /etc/mtab at all.
Ok.. I gotta you now... and I did take a few minutes to look into what
something like this would take... I quickly came to the realization
that adding all complexity to make a system file, that nobody see or 
care about, more aesthetic really not worth it and not necessary, IMHO....

Point being,  umount is so simple when it comes to umounting a nfs4 file 
system... It basically does nothing! Which is a beautiful thing! So to added 
all the code (on both the mount and umount side) to translate
'-t nfs -o v4' into nfs4 (which  would have to happen since 
del_mtab() takes a fs type) is just not worth it... Especially when
the other option is adding no code to the umount side...  


steved.