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Date:   Wed, 9 Sep 2020 16:25:34 -0400
To:     Anna Schumaker <schumaker.anna@gmail.com>
Cc:     "J. Bruce Fields" <bfields@redhat.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v5 2/5] NFSD: Add READ_PLUS data support
Message-ID: <20200909202534.GC3894@fieldses.org>
References: <20200908162559.509113-1-Anna.Schumaker@Netapp.com>
 <20200908162559.509113-3-Anna.Schumaker@Netapp.com>
 <20200908194245.GB6256@pick.fieldses.org>
 <CAFX2Jfkt0Qv1oO6iEr21N3zjkvE7VyKQQ47g2vQ4PHV6xmgrSg@mail.gmail.com>
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From:   bfields@fieldses.org (J. Bruce Fields)
Sender: linux-nfs-owner@vger.kernel.org
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On Wed, Sep 09, 2020 at 12:53:18PM -0400, Anna Schumaker wrote:
> On Tue, Sep 8, 2020 at 3:42 PM J. Bruce Fields <bfields@redhat.com> wrote:
> >
> > On Tue, Sep 08, 2020 at 12:25:56PM -0400, schumaker.anna@gmail.com wrote:
> > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > >
> > > This patch adds READ_PLUS support for returning a single
> > > NFS4_CONTENT_DATA segment to the client. This is basically the same as
> > > the READ operation, only with the extra information about data segments.
> > >
> > > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > >
> > > ---
> > > v5: Fix up nfsd4_read_plus_rsize() calculation
> > > ---
> > >  fs/nfsd/nfs4proc.c | 20 +++++++++++
> > >  fs/nfsd/nfs4xdr.c  | 83 ++++++++++++++++++++++++++++++++++++++++++++--
> > >  2 files changed, 101 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > index eaf50eafa935..0a3df5f10501 100644
> > > --- a/fs/nfsd/nfs4proc.c
> > > +++ b/fs/nfsd/nfs4proc.c
> > > @@ -2591,6 +2591,19 @@ static inline u32 nfsd4_read_rsize(struct svc_rqst *rqstp, struct nfsd4_op *op)
> > >       return (op_encode_hdr_size + 2 + XDR_QUADLEN(rlen)) * sizeof(__be32);
> > >  }
> > >
> > > +static inline u32 nfsd4_read_plus_rsize(struct svc_rqst *rqstp, struct nfsd4_op *op)
> > > +{
> > > +     u32 maxcount = svc_max_payload(rqstp);
> > > +     u32 rlen = min(op->u.read.rd_length, maxcount);
> > > +     /*
> > > +      * Worst case is a single large data segment, so make
> > > +      * sure we have enough room to encode that
> > > +      */
> >
> > After the last patch we allow an unlimited number of segments.  So a
> > zillion 1-byte segments is also possible, and is a worse case.
> >
> > Possible ways to avoid that kind of thing:
> >
> >         - when encoding, stop and return a short read if the xdr-encoded
> >           result would exceed the limit calculated here.
> 
> Doesn't this happen automatically through calls to xdr_reserve_space()?

No, xdr_reserve_space() will keep us from running out of buffer
completely, but it won't check that ops come in under the estimates made
in read_plus_rsize().

--b.

> 
> >         - round SEEK_HOLE results up to the nearest (say) 512 bytes, and
> >           SEEK_DATA result down to the nearest 512 bytes.  May also need
> >           some logic to avoid encoding 0-length segments.
> >         - talk to linux-fsdevel, see if we can get a minimum hole
> >           alignment guarantee from filesystems.
> >
> > I'm thinking #1 is simplest.
> >
> > --b.
> >
> > > +     u32 seg_len = 1 + 2 + 1;
> > > +
> > > +     return (op_encode_hdr_size + 2 + seg_len + XDR_QUADLEN(rlen)) * sizeof(__be32);
> > > +}
> > > +
> > >  static inline u32 nfsd4_readdir_rsize(struct svc_rqst *rqstp, struct nfsd4_op *op)
> > >  {
> > >       u32 maxcount = 0, rlen = 0;
> > > @@ -3163,6 +3176,13 @@ static const struct nfsd4_operation nfsd4_ops[] = {
> > >               .op_name = "OP_COPY",
> > >               .op_rsize_bop = nfsd4_copy_rsize,
> > >       },
> > > +     [OP_READ_PLUS] = {
> > > +             .op_func = nfsd4_read,
> > > +             .op_release = nfsd4_read_release,
> > > +             .op_name = "OP_READ_PLUS",
> > > +             .op_rsize_bop = nfsd4_read_plus_rsize,
> > > +             .op_get_currentstateid = nfsd4_get_readstateid,
> > > +     },
> > >       [OP_SEEK] = {
> > >               .op_func = nfsd4_seek,
> > >               .op_name = "OP_SEEK",
> > > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > > index 0be194de4888..26d12e3edf33 100644
> > > --- a/fs/nfsd/nfs4xdr.c
> > > +++ b/fs/nfsd/nfs4xdr.c
> > > @@ -2173,7 +2173,7 @@ static const nfsd4_dec nfsd4_dec_ops[] = {
> > >       [OP_LAYOUTSTATS]        = (nfsd4_dec)nfsd4_decode_notsupp,
> > >       [OP_OFFLOAD_CANCEL]     = (nfsd4_dec)nfsd4_decode_offload_status,
> > >       [OP_OFFLOAD_STATUS]     = (nfsd4_dec)nfsd4_decode_offload_status,
> > > -     [OP_READ_PLUS]          = (nfsd4_dec)nfsd4_decode_notsupp,
> > > +     [OP_READ_PLUS]          = (nfsd4_dec)nfsd4_decode_read,
> > >       [OP_SEEK]               = (nfsd4_dec)nfsd4_decode_seek,
> > >       [OP_WRITE_SAME]         = (nfsd4_dec)nfsd4_decode_notsupp,
> > >       [OP_CLONE]              = (nfsd4_dec)nfsd4_decode_clone,
> > > @@ -4597,6 +4597,85 @@ nfsd4_encode_offload_status(struct nfsd4_compoundres *resp, __be32 nfserr,
> > >               return nfserr_resource;
> > >       p = xdr_encode_hyper(p, os->count);
> > >       *p++ = cpu_to_be32(0);
> > > +     return nfserr;
> > > +}
> > > +
> > > +static __be32
> > > +nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> > > +                         struct nfsd4_read *read,
> > > +                         unsigned long maxcount,  u32 *eof)
> > > +{
> > > +     struct xdr_stream *xdr = &resp->xdr;
> > > +     struct file *file = read->rd_nf->nf_file;
> > > +     int starting_len = xdr->buf->len;
> > > +     __be32 nfserr;
> > > +     __be32 *p, tmp;
> > > +     __be64 tmp64;
> > > +
> > > +     /* Content type, offset, byte count */
> > > +     p = xdr_reserve_space(xdr, 4 + 8 + 4);
> > > +     if (!p)
> > > +             return nfserr_resource;
> > > +
> > > +     read->rd_vlen = xdr_reserve_space_vec(xdr, resp->rqstp->rq_vec, maxcount);
> > > +     if (read->rd_vlen < 0)
> > > +             return nfserr_resource;
> > > +
> > > +     nfserr = nfsd_readv(resp->rqstp, read->rd_fhp, file, read->rd_offset,
> > > +                         resp->rqstp->rq_vec, read->rd_vlen, &maxcount, eof);
> > > +     if (nfserr)
> > > +             return nfserr;
> > > +
> > > +     tmp = htonl(NFS4_CONTENT_DATA);
> > > +     write_bytes_to_xdr_buf(xdr->buf, starting_len,      &tmp,   4);
> > > +     tmp64 = cpu_to_be64(read->rd_offset);
> > > +     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);
> > > +     return nfs_ok;
> > > +}
> > > +
> > > +static __be32
> > > +nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
> > > +                    struct nfsd4_read *read)
> > > +{
> > > +     unsigned long maxcount;
> > > +     struct xdr_stream *xdr = &resp->xdr;
> > > +     struct file *file;
> > > +     int starting_len = xdr->buf->len;
> > > +     int segments = 0;
> > > +     __be32 *p, tmp;
> > > +     u32 eof;
> > > +
> > > +     if (nfserr)
> > > +             return nfserr;
> > > +     file = read->rd_nf->nf_file;
> > > +
> > > +     /* eof flag, segment count */
> > > +     p = xdr_reserve_space(xdr, 4 + 4);
> > > +     if (!p)
> > > +             return nfserr_resource;
> > > +     xdr_commit_encode(xdr);
> > > +
> > > +     maxcount = svc_max_payload(resp->rqstp);
> > > +     maxcount = min_t(unsigned long, maxcount,
> > > +                      (xdr->buf->buflen - xdr->buf->len));
> > > +     maxcount = min_t(unsigned long, maxcount, read->rd_length);
> > > +
> > > +     eof = read->rd_offset >= i_size_read(file_inode(file));
> > > +     if (!eof) {
> > > +             nfserr = nfsd4_encode_read_plus_data(resp, read, maxcount, &eof);
> > > +             segments++;
> > > +     }
> > > +
> > > +     if (nfserr)
> > > +             xdr_truncate_encode(xdr, starting_len);
> > > +     else {
> > > +             tmp = htonl(eof);
> > > +             write_bytes_to_xdr_buf(xdr->buf, starting_len,     &tmp, 4);
> > > +             tmp = htonl(segments);
> > > +             write_bytes_to_xdr_buf(xdr->buf, starting_len + 4, &tmp, 4);
> > > +     }
> > >
> > >       return nfserr;
> > >  }
> > > @@ -4974,7 +5053,7 @@ static const nfsd4_enc nfsd4_enc_ops[] = {
> > >       [OP_LAYOUTSTATS]        = (nfsd4_enc)nfsd4_encode_noop,
> > >       [OP_OFFLOAD_CANCEL]     = (nfsd4_enc)nfsd4_encode_noop,
> > >       [OP_OFFLOAD_STATUS]     = (nfsd4_enc)nfsd4_encode_offload_status,
> > > -     [OP_READ_PLUS]          = (nfsd4_enc)nfsd4_encode_noop,
> > > +     [OP_READ_PLUS]          = (nfsd4_enc)nfsd4_encode_read_plus,
> > >       [OP_SEEK]               = (nfsd4_enc)nfsd4_encode_seek,
> > >       [OP_WRITE_SAME]         = (nfsd4_enc)nfsd4_encode_noop,
> > >       [OP_CLONE]              = (nfsd4_enc)nfsd4_encode_noop,
> > > --
> > > 2.28.0
> > >
> >