On Fri, Aug 28, 2020 at 6:19 PM J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
>
> On Mon, Aug 17, 2020 at 12:53:09PM -0400, schumaker.anna@xxxxxxxxx wrote:
> > From: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
> >
> > But only one of each right now. We'll expand on this in the next patch.
> >
> > Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
> > ---
> > fs/nfsd/nfs4xdr.c | 51 ++++++++++++++++++++++++++++++++++-------------
> > 1 file changed, 37 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > index 2fa39217c256..3f4860103b25 100644
> > --- a/fs/nfsd/nfs4xdr.c
> > +++ b/fs/nfsd/nfs4xdr.c
> > @@ -4373,7 +4373,7 @@ nfsd4_encode_offload_status(struct nfsd4_compoundres *resp, __be32 nfserr,
> > static __be32
> > nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> > struct nfsd4_read *read,
> > - unsigned long maxcount, u32 *eof)
> > + unsigned long *maxcount, u32 *eof)
> > {
> > struct xdr_stream *xdr = &resp->xdr;
> > struct file *file = read->rd_nf->nf_file;
> > @@ -4384,19 +4384,19 @@ nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> > __be64 tmp64;
> >
> > if (hole_pos > read->rd_offset)
> > - maxcount = min_t(unsigned long, maxcount, hole_pos - read->rd_offset);
> > + *maxcount = min_t(unsigned long, *maxcount, hole_pos - read->rd_offset);
> >
> > /* 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);
> > + 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);
> > + resp->rqstp->rq_vec, read->rd_vlen, maxcount, eof);
> > if (nfserr)
> > return nfserr;
> >
> > @@ -4404,7 +4404,7 @@ nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> > 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);
> > + tmp = htonl(*maxcount);
> > write_bytes_to_xdr_buf(xdr->buf, starting_len + 12, &tmp, 4);
> > return nfs_ok;
> > }
> > @@ -4412,11 +4412,19 @@ nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> > static __be32
> > nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp,
> > struct nfsd4_read *read,
> > - unsigned long maxcount, u32 *eof)
> > + unsigned long *maxcount, u32 *eof)
> > {
> > struct file *file = read->rd_nf->nf_file;
> > + loff_t data_pos = vfs_llseek(file, read->rd_offset, SEEK_DATA);
>
> Everywhere I see fs_llseek()s and i_size_read()s, I start wondering
> where there might be races. E.g.:
>
> > + unsigned long count;
> > __be32 *p;
> >
> > + if (data_pos == -ENXIO)
> > + data_pos = i_size_read(file_inode(file));
> > + else if (data_pos <= read->rd_offset)
> > + return nfserr_resource;
>
> I think that means a concurrent truncate would cause us to fail the
> entire read, when I suspect the right thing to do is to return a short
> (but successful) read.
Okay. I think I can do that in nfsd4_encode_read_plus() by checking if
there is an error and if we've encoded at least 1 segment.
>
> --b.
>
> > + count = data_pos - read->rd_offset;
> > +
> > /* Content type, offset, byte count */
> > p = xdr_reserve_space(&resp->xdr, 4 + 8 + 8);
> > if (!p)
> > @@ -4424,9 +4432,10 @@ nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp,
> >
> > *p++ = htonl(NFS4_CONTENT_HOLE);
> > p = xdr_encode_hyper(p, read->rd_offset);
> > - p = xdr_encode_hyper(p, maxcount);
> > + p = xdr_encode_hyper(p, count);
> >
> > - *eof = (read->rd_offset + maxcount) >= i_size_read(file_inode(file));
> > + *eof = (read->rd_offset + count) >= i_size_read(file_inode(file));
> > + *maxcount = min_t(unsigned long, count, *maxcount);
> > return nfs_ok;
> > }
> >
> > @@ -4434,7 +4443,7 @@ static __be32
> > nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
> > struct nfsd4_read *read)
> > {
> > - unsigned long maxcount;
> > + unsigned long maxcount, count;
> > struct xdr_stream *xdr = &resp->xdr;
> > struct file *file;
> > int starting_len = xdr->buf->len;
> > @@ -4457,6 +4466,7 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
> > maxcount = min_t(unsigned long, maxcount,
> > (xdr->buf->buflen - xdr->buf->len));
> > maxcount = min_t(unsigned long, maxcount, read->rd_length);
> > + count = maxcount;
> >
> > eof = read->rd_offset >= i_size_read(file_inode(file));
> > if (eof)
> > @@ -4465,13 +4475,26 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
> > pos = vfs_llseek(file, read->rd_offset, SEEK_DATA);
> > if (pos == -ENXIO)
> > pos = i_size_read(file_inode(file));
> > + else if (pos < 0)
> > + pos = read->rd_offset;
> >
> > - if (pos > read->rd_offset) {
> > - maxcount = pos - read->rd_offset;
> > - nfserr = nfsd4_encode_read_plus_hole(resp, read, maxcount, &eof);
> > + if (pos == read->rd_offset) {
> > + maxcount = count;
> > + nfserr = nfsd4_encode_read_plus_data(resp, read, &maxcount, &eof);
> > + if (nfserr)
> > + goto out;
> > + count -= maxcount;
> > + read->rd_offset += maxcount;
> > segments++;
> > - } else {
> > - nfserr = nfsd4_encode_read_plus_data(resp, read, maxcount, &eof);
> > + }
> > +
> > + if (count > 0 && !eof) {
> > + maxcount = count;
> > + nfserr = nfsd4_encode_read_plus_hole(resp, read, &maxcount, &eof);
> > + if (nfserr)
> > + goto out;
> > + count -= maxcount;
> > + read->rd_offset += maxcount;
> > segments++;
> > }
> >
> > --
> > 2.28.0
> >
>
