On Fri, Feb 5, 2016 at 2:03 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote: > 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. > Hi Olga, I understood what you said, but you cannot have multiple replies to the same RPC call. It doesn't matter if it was a replay, if the server replies AUTH_ERROR, then it is saying "I'm not executing this". 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
