On Thu, May 30, 2019 at 1:05 PM Tom Talpey <tom@xxxxxxxxxx> wrote: > > On 5/29/2019 8:41 PM, NeilBrown wrote: > > I've also re-arrange the patches a bit, merged two, and remove the > > restriction to TCP and NFSV4.x,x>=1. Discussions seemed to suggest > > these restrictions were not needed, I can see no need. > > I believe the need is for the correctness of retries. Because NFSv2, > NFSv3 and NFSv4.0 have no exactly-once semantics of their own, server > duplicate request caches are important (although often imperfect). > These caches use client XID's, source ports and addresses, sometimes > in addition to other methods, to detect retry. Existing clients are > careful to reconnect with the same source port, to ensure this. And > existing servers won't change. Retries are already bound to the same connection so there shouldn't be an issue of a retransmission coming from a different source port. > Multiple connections will result in multiple source ports, and possibly > multiple source addresses, meaning retried client requests may be > accepted as new, rather than having any chance of being recognized as > retries. > > NFSv4.1+ don't have this issue, but removing the restrictions would > seem to break the downlevel mounts. > > Tom. >
