On Wed, Sep 09, 2020 at 12:51:38PM -0400, Anna Schumaker wrote:
> On Tue, Sep 8, 2020 at 3:49 PM J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
> >
> > On Tue, Sep 08, 2020 at 12:25:58PM -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>
> > > ---
> > > v5: If we've already encoded a segment, then return a short read if
> > > later segments return an error for some reason.
> > > ---
> > > fs/nfsd/nfs4xdr.c | 54 ++++++++++++++++++++++++++++++++++-------------
> > > 1 file changed, 39 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > > index 45159bd9e9a4..856606263c1d 100644
> > > --- a/fs/nfsd/nfs4xdr.c
> > > +++ b/fs/nfsd/nfs4xdr.c
> > > @@ -4603,7 +4603,7 @@ 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;
> > > @@ -4614,19 +4614,19 @@ 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;
> > >
> > > @@ -4634,7 +4634,7 @@ 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;
> > > }
> > > @@ -4642,11 +4642,19 @@ 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);
> > > + 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 there's still a race here:
> >
> > vfs_llseek(.,0,SEEK_HOLE) returns 1024
> > read 1024 bytes of data
> > another process fills the hole
> > vfs_llseek(.,1024,SEEK_DATA) returns 1024
> > code above returns nfserr_resource
> >
> > We end up returning an error to the client when we should have just
> > returned more data.
>
> As long as we've encoded at least one segment successfully, we'll
> actually return a short read in this case (as of the most recent
> patches). I tried implementing a check for what each segment actually
> was before encoding, but it lead to a lot of extra lseeks (so
> potential for races / performance problems on btrfs). Returning a
> short read seemed like a better approach to me.
Argh, right, I forgot the "if (nfserr && segments == 0)" at the end of
nfsd4_encode_read_plus().
It's still possible to get a spurious error return if this happens at
the very start of the READ_PLUS, though. Hm. Might be better to just
encode another data segment?
--b.
>
> Anna
>
> >
> > --b.
> >
> > > + count = data_pos - read->rd_offset;
> > > +
> > > /* Content type, offset, byte count */
> > > p = xdr_reserve_space(&resp->xdr, 4 + 8 + 8);
> > > if (!p)
> > > @@ -4654,9 +4662,10 @@ 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;
> > > }
> > >
> > > @@ -4664,7 +4673,7 @@ 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;
> > > @@ -4687,6 +4696,7 @@ 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)
> > > @@ -4695,24 +4705,38 @@ 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++;
> > > }
> > >
> > > out:
> > > - if (nfserr)
> > > + if (nfserr && segments == 0)
> > > 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);
> > > + nfserr = nfs_ok;
> > > }
> > >
> > > return nfserr;
> > > --
> > > 2.28.0
> > >
> >
