Re: [PATCH] rpc.nfsd: mount up nfsdfs is it doesn't appear to be mounted yet

[Steve Dickson <SteveD@redhat.com>]

On 08/31/2010 08:43 AM, Jeff Layton wrote:
> On Tue, 31 Aug 2010 08:24:57 -0400
> Steve Dickson <SteveD@redhat.com> wrote:
> 
>>
>>
>> On 08/30/2010 01:48 PM, Jeff Layton wrote:
>>> On Mon, 30 Aug 2010 12:53:16 -0400
>>> Steve Dickson <SteveD@redhat.com> wrote:
>>>>>
>>>>> Hmmm...if I had known that it was ok to stop supporting old kernels,
>>>>> the IPv6 support for rpc.nfsd would have been a heck of a lot easier to
>>>>> implement.
>>>> I thought you said the legacy interface would not work with IPV6 or
>>>> did I misunderstand you? 
>>>>
>>>
>>> Sorry, forgot to answer this part. IPv6 indeed will not work when using
>>> the legacy interface. In order to get the IPv6 code in though, I ended
>>> up rewriting a large swath of rpc.nfsd. That task would have been
>>> easier had I not needed to deal with the legacy nfsctl() interface.
>>>
>> So I'm thinking this the final nail in the coffin of the legacy interface
>> at least in rpc.nfsd. So if /proc/fs/nfsd filesystem is not or can not
>> be mounted then rpc.nfsd should fail... IMHO...
>>
>> Maybe something like:
>>
>> if (stat("/proc/fs/nfsd") < 0) {
> 
> This needs to check a file within /proc/fs/nfsd. The nfsd "dir" may
> already exist even if it's not mounted. I chose "threads" but any file
> in there would do...
> 
>>     if (system("mount /proc/fs/nfsd") < 0) {
>>         xlog(L_ERROR, "Unable to mount /proc/fs/nfsd");
>>         exit 0;
>>     }
>> }
>>
>> steved.
> 
> That will universally fail, at least on most distros.
By no means was I meaning this was working code... 
I was just trying to introduced logic of: check to see if  
/proc/fs/nfsd exists, if not, mount it. If the mount fails, exit.
Detail to be worked out later... 

> 
> 
> When you go to mount /proc/fs/nfsd, the system does a request_module()
> for nfsd.ko. On most distros (e.g. Fedora or RHEL), modprobe will then
> automatically mount up /proc/fs/nfsd. request_module will then return
> and the mount attempt will proceed. 
Yeah I know... I am one that taught modprobe how to that... at least 
in the RH distros... ;-) Although I believe the actual mechanics
have changed over the years... 

> The mount will then fail because
> it's now already mounted, and the system() call will return non-zero.
Isn't this reason to do the stat() before the mount? So you will not try to
mount the FS if is already mounted? 

> 
> That's the main reason I ignored the return code from system() in the
> original patch. What you could do is recheck whether the file exists
> after the mount attempt, and then fail if it doesn't.
My point was we need to know if the mount did or did not
work to take the appropriate action... 
 
> 
> Is that really what we want to do here though? How does ditching the
> legacy interface move us forward now? If we had decided to do this a
> year ago when I was overhauling rpc.nfsd, it might have made sense. The
> code exists now though and it works. Ripping this out seems more
> disruptive than just leaving it in.
I believe we are talking about 4 lines of code at the bottom of nfssvc_threads()
I don't think that would be too disruptive... 

steved.

> 
> To keep this on track, I think we need to treat this as 2 separate
> discussions:
> 
> 1) how to we ensure that /proc/fs/nfsd is actually mounted when
> rpc.nfsd is run?
> 
> 2) what do we do about the legacy nfsctl() interface?
> 
> These are separate but related questions...