On Fri, Feb 5, 2016 at 1:31 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > On Fri, Feb 5, 2016 at 12:01 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote: >> On Fri, Feb 5, 2016 at 11:44 AM, Trond Myklebust >> <trond.myklebust@xxxxxxxxxxxxxxx> wrote: >>> On Fri, Feb 5, 2016 at 10:37 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote: >>>> I have a question regarding the implementation of sunrpc use of XID >>>> when the client receives an AUTH_ERROR. The code (clnt.c line 1933) >>>> explicitly comments that a new XID should be acquired and releases the >>>> currently rpc task (and gets a new one). Why is that? Since the >>>> operation is "replayed" but with the new credentials, why shouldn't >>>> the same XID be used? >>>> >>>> The RPC RFC says that XID is used by the server to detect >>>> retransmissions. It's not clear if in the specs means "retransmission" >>>> == tcp retransmissions. If so then it explains why the client uses the >>>> same XID. >>>> >>> >>> The questions you are asking come under the header "RPC lore" rather >>> than "RPC law". The use of XIDs as a basis for replay caching is not >>> speced out in any RFC. The closest thing we have in the form of >>> documentation is Ric Werme's presentation at the 1996 Connectathon: >>> http://nfsv4bat.org/Documents/ConnectAThon/1996/werme1.pdf >>> >>> Basically, those comments are there in the Linux code to denote issues >>> found when interoperability testing with server implementations that >>> are probably now long dead, but might still be in use somewhere. >> >> Would you consider changing this to use the same XID in case of >> redoing the operation due to the AUTH_ERROR? >> >> The issue it causes (one of the) server's implementation is of the >> following nature: >> 1. client sends an operation to the server. the server process the >> operation but before replying back to the server has an issue and >> resets the connection. >> 2. client re-establishes the connection and replays the RPC. the >> server now fails with the AUTH_ERROR. >> 3. client establishes a new connection and replays the same NFS >> operation over the new XID. The server cached the operation but since >> the last operation arrives with the new XID it won't find the entry in >> the cache. It's problematic when the operation is like REMOVE. >> >> I realize this is why nfs4.1 session were introduce to solve these >> non-idenpotency issues but using the same XID seems like the right >> idea since it is the same operation. >> >> If you don't have objections to the change, I can ask on the IETF list >> to see if any servers will object to such change. > > What you describe is a clear and obvious server bug. It is not a > client bug, and is not something that I'd find acceptable as > justification for changing the client code. > > The server should not be replying AUTH_ERROR and then processing the > RPC anyway. That's not behaviour that is sanctioned by the RPC spec. Perhaps I wasn't clear let me try again. In the first step, the server processes request and does not reply with an AUTH_ERROR but instead resets a connection but it has already populated it's replay cache. Client reestablishes connection resends exactly the same bytes but gets back an AUTH_ERROR (server does not process the operation). It's the recovery from this error that's in question. > > Cheers > Trond -- 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
