Re: [PATCH 0/2] showmount bug fixes

[Steve Dickson <SteveD@redhat.com>]

On 01/07/2010 01:38 PM, Chuck Lever wrote:
> 
> On Jan 7, 2010, at 12:52 PM, Steve Dickson wrote:
> 
>>
>>
>> On 01/07/2010 11:26 AM, Chuck Lever wrote:
>>> Hi Steve-
>>>
>>> As promised, a couple of bug fixes for the recent improvements to the
>>> showmount command.
>>>
>>> ---
>>>
>>> Chuck Lever (2):
>>>      showmount: Use CLNT_CONTROL for version fallback
>> Why is calling CLNT_CONTROL() verses calling clnt_create again
>> so much better?? In between failures the server status could
>> change so why not just ping it again??
>>
> 
> The clnt_create(3) library call is quite heavyweight.  It does a DNS
> lookup via its own transport socket, a GETPORT via its own transport
> socket, then creates and connects a socket to do the application's RPC
> work.
> 
> Each time showmount calls clnt_create(3), the library will set up a
> socket for the DNS lookup (usually but not always UDP), set up a socket
> to do a GETPORT, and then set up a third socket for the MNTPROC_EXPORT
> request.  That's three sockets, each time through your retry loop.
> 
> When contacting a MNTv1-only server over TCP, the showmount command can
> leave up to six TCP sockets in TIME_WAIT (not counting sockets used for
> DNS) for 120 seconds after the command exits, if it doesn't use
> CLNT_CONTROL.
Now really... who do you know that runs an v2 only server... 
I would call that badly misconfigured server... and I just
don't think it happens...because if it did, the bug would have
become much more prevalent a long time ago...  

Remember the goal of this patch is to deal with v3 only servers...
plus I kinda like the idea having applications re-querying the
server since configuration do indeed change... 

steved.
 

> 
> In the TCP case, CLNT_CONTROL leaves the application's transport socket
> connected.  This means showmount doesn't perform any additional DNS or
> GETPORT requests (it does just one of each), and then one transport
> socket is used for all the MNTPROC_EXPORT request retries.  Thus, with
> CLNT_CONTROL, showmount uses one TCP socket for a single GETPORT, and
> one socket to do the MNTPROC_EXPORT requests.
> 
> So in every case, showmount will use just two transport sockets (not
> counting the DNS query).  It's behavior is no different than your
> original patch if the server supports MNTv3, but much more efficient for
> the MNTv1-only case.
> 
> Leaving multiple sockets in TIME_WAIT is a regression from the original
> showmount behavior, hence this bug fix.  If a customer reported this
> problem, you wouldn't hesitate to apply this fix.  I'm not sure why you
> find this controversial.
> 
> -- 
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
> 
> 
>