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 > > > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
