Re: [PATCH 15/16] nfsd: Fixes for nfsd4_encode_read_plus_data()

[Chuck Lever <chucklever@gmail.com>]

> On Dec 9, 2020, at 11:39 AM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Wed, 2020-12-09 at 11:16 -0500, Chuck Lever wrote:
>> Hey-
>> 
>>> On Dec 9, 2020, at 9:48 AM, trondmy@kernel.org wrote:
>>> 
>>> From: Trond Myklebust <trond.myklebust@hammerspace.com>
>>> 
>>> Ensure that we encode the data payload + padding, and that we
>>> truncate
>>> the preallocated buffer to the actual read size.
>> 
>> Did you intend to merge 15/16 and 16/16 through your tree?
> 
> No. They can go through the nfsd tree. I included them here because
> they are necessary in order to pass the xfstests.

Would it be OK if they went in 5.11-rc? I've got the initial
merge tag prepared already. If they can't wait, let me know.


>> Can the patch descriptions say a little more about why these
>> changes are necessary? If they fix a misbehavior, describe
>> the problem.
> 
> It's the same problem and solution that exists in the READ code.
> 
> nfsd_readv() doesn't necessarily return the same number of bytes that
> we requested and preallocated buffer space for. So to deal with that,
> we have to truncate the preallocated buffer.

Huh. I thought it was doing that already? Oh, that's just for
the cases where the server returns an error status. The
READ_PLUS encoder incorrectly does not do that truncation for
short READs... got it.


> Finally, we have to write zeros into the padding bytes after the read
> buffer.

Right. Then the problem statement is that the server's READ_PLUS
XDR encoder isn't padding the read buffer properly.

Quibble: perhaps these are two separate issues that each deserve
their own patches with Fixes: tags (and if you re-post these,
please add a Fixes: tag to 16/16 too).

Thanks!


>>> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
>>> ---
>>> fs/nfsd/nfs4xdr.c | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>> 
>>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>>> index 833a2c64dfe8..26f6e277101d 100644
>>> --- a/fs/nfsd/nfs4xdr.c
>>> +++ b/fs/nfsd/nfs4xdr.c
>>> @@ -4632,6 +4632,7 @@ nfsd4_encode_read_plus_data(struct
>>> nfsd4_compoundres *resp,
>>>                             resp->rqstp->rq_vec, read->rd_vlen,
>>> maxcount, eof);
>>>         if (nfserr)
>>>                 return nfserr;
>>> +       xdr_truncate_encode(xdr, starting_len + 16 +
>>> xdr_align_size(*maxcount));
>>> 
>>>         tmp = htonl(NFS4_CONTENT_DATA);
>>>         write_bytes_to_xdr_buf(xdr->buf, starting_len,      &tmp,  
>>> 4);
>>> @@ -4639,6 +4640,10 @@ nfsd4_encode_read_plus_data(struct
>>> nfsd4_compoundres *resp,
>>>         write_bytes_to_xdr_buf(xdr->buf, starting_len + 4,  &tmp64,
>>> 8);
>>>         tmp = htonl(*maxcount);
>>>         write_bytes_to_xdr_buf(xdr->buf, starting_len + 12, &tmp,  
>>> 4);
>>> +
>>> +       tmp = xdr_zero;
>>> +       write_bytes_to_xdr_buf(xdr->buf, starting_len + 16 +
>>> *maxcount, &tmp,
>>> +                              xdr_pad_size(*maxcount));
>>>         return nfs_ok;
>>> }
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com

--
Chuck Lever
chucklever@gmail.com