• Neil Brown's avatar
    [PATCH] kNFSd: Giant patch importing NFSv4 server functionality · b59e9ac5
    Neil Brown authored
    Now that all the hooks are in place, this large patch imports all
    of the new code for the NFSv4 server.
    
    This patch makes almost no changes to the existing nfsd codebase
    (these have been taken care of by the preceding patches).
    
    One aspect of the NFSv4 code deserves comment.  The most natural scheme
    for processing a COMPOUND request would seem to be:
      1a. XDR decode phase, decode args of all operations
      2a. processing phase, process all operations
      3a. XDR encode phase, encode results of all operations
    
    However, we use a scheme which works as follows:
      1b. XDR decode phase, decode args of all operations
      2b. For each operation,
            process the operation
            encode the result
    
    To see what is wrong with the first scheme, consider a COMPOUND
    of the form READ REMOVE.  Since the last bit of processing for
    the READ request occurs in XDR encode, we might discover in step
    3a that the READ request should return an error.  Therefore, the
    REMOVE request should not be processed at all.  This is a fatal
    problem, since the REMOVE was already been done in step 2a!
    
    Another type of problem would occur in a COMPOUND of the form
    READ WRITE.  Assume that both operations succeed.  Under scheme
    (a), the WRITE is actually performed _before_ the READ (since
    the "real" READ is really done during XDR encode).  This is
    certainly incorrect if the READ and WRITE ranges overlap.
    
    These examples might seem a little artificial, but nevertheless
    it does seem that in order to process a COMPOUND correctly in
    all cases, we need to use scheme (b) instead of scheme (a).
    
    (To construct less artificial examples, just substitute GETATTR
     for READ in the examples above.  This works because the "real"
     GETATTR is done during XDR encode: one would really have to
     bend over backwards in order to arrange things otherwise.)
    b59e9ac5
nfs4xdr.c 45.3 KB