Re: [PATCH/RFC] NFS: handle NFSv4.1 server that doesn't support NFS4_OPEN_CLAIM_DELEG_CUR_FH

[NeilBrown <neilb@suse.de>]

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On Thu, Dec 19 2019, Trond Myklebust wrote:

> On Thu, 2019-12-19 at 13:56 +1100, NeilBrown wrote:
>> On Wed, Dec 18 2019, Trond Myklebust wrote:
>> 
>> > On Thu, 2019-12-19 at 09:47 +1100, NeilBrown wrote:
>> > > If an NFSv4.1 server doesn't support NFS4_OPEN_CLAIM_DELEG_CUR_FH
>> > > (e.g. Linux 3.0), and a newer NFS client tries to use it to claim
>> > > an open before returning a delegation, the server might return
>> > > NFS4ERR_BADXDR.
>> > > That is what Linux 3.0 does, though the RFC doesn't seem to be
>> > > explicit
>> > > on which flags must be supported, and what error can be returned
>> > > for
>> > > unsupported flags.
>> > 
>> > NFS4ERR_BADXDR is defined in RFC5661, section 15.1.1.1 as meaning
>> > 
>> > "The arguments for this operation do not match those specified in
>> > the
>> > XDR definition."
>> > 
>> > That's clearly not the case here, so I'd chalk this down to a
>> > fairly
>> > blatant server bug, at which point it makes no sense to fix it in
>> > the
>> > client.
>> 
>> Ok, but the RFC seems to suggest it is OK to not support this flag,
>> so
>> suppose I fixed the server to return NFS4ERR_NOTSUPP instead.
>> The client still wouldn't handle this response gracefully.
>> 
>
> NFS4ERR_NOTSUPP is wrong too as the OPEN operation is clearly
> supported. The only error that might make sense is NFS4ERR_INVAL:
>
> "15.1.1.4.  NFS4ERR_INVAL (Error Code 22)
>
>    The arguments for this operation are not valid for some reason, even
>    though they do match those specified in the XDR definition for the
>    request."
>
> That said, why do we care about supporting NFSv4.1 on this server? It
> is clearly broken.

I care about it because a customer has a support contract, but that
isn't your problem.

I would think "we" care about it because we want to support the spec,
and the spec (RFC 5661 section 2.4) says:

                                                        where the server
   supports neither the CLAIM_DELEGATE_PREV nor CLAIM_DELEG_CUR_FH claim
   types

Also you have code in the client to handle the possibility that an
NFSv4.1 or later server might not handle some features of OPEN.
Three separate features are grouped under "NFS_CAP_ATOMIC_OPEN_V1":
If this isn't set, we fall back:

        case NFS4_OPEN_CLAIM_FH:
                return NFS4_OPEN_CLAIM_NULL;
        case NFS4_OPEN_CLAIM_DELEG_CUR_FH:
                return NFS4_OPEN_CLAIM_DELEGATE_CUR;
        case NFS4_OPEN_CLAIM_DELEG_PREV_FH:
                return NFS4_OPEN_CLAIM_DELEGATE_PREV;

However nfs4_map_atomic_open_claim() is not called when
NFS4_OPEN_CLAIM_DELEG_CUR_FH is tried, and fails.  This appears
to be an omission in the code.

Thanks,
NeilBrown

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