NFSD: Hoist rq_vec preparation into nfsd_read() [step two]

Now that the preparation of an rq_vec has been removed from the
generic read path, nfsd_splice_read() no longer needs to reset
rq_next_page.

nfsd4_encode_read() calls nfsd_splice_read() directly. As far as I
can ascertain, resetting rq_next_page for NFSv4 splice reads is
unnecessary because rq_next_page is already set correctly.

Moreover, resetting it might even be incorrect if previous
operations in the COMPOUND have already consumed at least a page of
the send buffer. I would expect that the result would be encoding
the READ payload over previously-encoded results.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -4103,12 +4103,12 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
 	__be32 zero = xdr_zero;
 	__be32 nfserr;
 
-	read->rd_vlen = xdr_reserve_space_vec(xdr, resp->rqstp->rq_vec, maxcount);
-	if (read->rd_vlen < 0)
+	if (xdr_reserve_space_vec(xdr, maxcount) < 0)
 		return nfserr_resource;
 
-	nfserr = nfsd_readv(resp->rqstp, read->rd_fhp, file, read->rd_offset,
-			    resp->rqstp->rq_vec, read->rd_vlen, &maxcount,
+	nfserr = nfsd_iter_read(resp->rqstp, read->rd_fhp, file,
+				read->rd_offset, &maxcount,
+				xdr->buf->page_len & ~PAGE_MASK,
 				&read->rd_eof);
 	read->rd_length = maxcount;
 	if (nfserr)

fs/nfsd/vfs.c

@@ -1003,6 +1003,18 @@ static __be32 nfsd_finish_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	}
 }
 
+/**
+ * nfsd_splice_read - Perform a VFS read using a splice pipe
+ * @rqstp: RPC transaction context
+ * @fhp: file handle of file to be read
+ * @file: opened struct file of file to be read
+ * @offset: starting byte offset
+ * @count: IN: requested number of bytes; OUT: number of bytes read
+ * @eof: OUT: set non-zero if operation reached the end of the file
+ *
+ * Returns nfs_ok on success, otherwise an nfserr stat value is
+ * returned.
+ */
 __be32 nfsd_splice_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 			struct file *file, loff_t offset, unsigned long *count,
 			u32 *eof)
@@ -1016,7 +1028,6 @@ __be32 nfsd_splice_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	ssize_t host_err;
 
 	trace_nfsd_read_splice(rqstp, fhp, offset, *count);
-	rqstp->rq_next_page = rqstp->rq_respages + 1;
 	host_err = splice_direct_to_actor(file, &sd, nfsd_direct_splice_actor);
 	return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
 }

include/linux/sunrpc/xdr.h

@@ -242,8 +242,7 @@ extern void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf,
 extern void xdr_init_encode_pages(struct xdr_stream *xdr, struct xdr_buf *buf,
 			   struct page **pages, struct rpc_rqst *rqst);
 extern __be32 *xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes);
-extern int xdr_reserve_space_vec(struct xdr_stream *xdr, struct kvec *vec,
-		size_t nbytes);
+extern int xdr_reserve_space_vec(struct xdr_stream *xdr, size_t nbytes);
 extern void __xdr_commit_encode(struct xdr_stream *xdr);
 extern void xdr_truncate_encode(struct xdr_stream *xdr, size_t len);
 extern void xdr_truncate_decode(struct xdr_stream *xdr, size_t len);

net/sunrpc/xdr.c

@@ -1070,22 +1070,22 @@ __be32 * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
 }
 EXPORT_SYMBOL_GPL(xdr_reserve_space);
 
-
 /**
  * xdr_reserve_space_vec - Reserves a large amount of buffer space for sending
  * @xdr: pointer to xdr_stream
- * @vec: pointer to a kvec array
  * @nbytes: number of bytes to reserve
  *
- * Reserves enough buffer space to encode 'nbytes' of data and stores the
- * pointers in 'vec'. The size argument passed to xdr_reserve_space() is
- * determined based on the number of bytes remaining in the current page to
- * avoid invalidating iov_base pointers when xdr_commit_encode() is called.
+ * The size argument passed to xdr_reserve_space() is determined based
+ * on the number of bytes remaining in the current page to avoid
+ * invalidating iov_base pointers when xdr_commit_encode() is called.
+ *
+ * Return values:
+ *   %0: success
+ *   %-EMSGSIZE: not enough space is available in @xdr
  */
-int xdr_reserve_space_vec(struct xdr_stream *xdr, struct kvec *vec, size_t nbytes)
+int xdr_reserve_space_vec(struct xdr_stream *xdr, size_t nbytes)
 {
-	int thislen;
-	int v = 0;
+	size_t thislen;
 	__be32 *p;
 
 	/*
@@ -1097,21 +1097,19 @@ int xdr_reserve_space_vec(struct xdr_stream *xdr, struct kvec *vec, size_t nbyte
 		xdr->end = xdr->p;
 	}
 
+	/* XXX: Let's find a way to make this more efficient */
 	while (nbytes) {
 		thislen = xdr->buf->page_len % PAGE_SIZE;
 		thislen = min_t(size_t, nbytes, PAGE_SIZE - thislen);
 
 		p = xdr_reserve_space(xdr, thislen);
 		if (!p)
-			return -EIO;
+			return -EMSGSIZE;
 
-		vec[v].iov_base = p;
-		vec[v].iov_len = thislen;
-		v++;
 		nbytes -= thislen;
 	}
 
-	return v;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(xdr_reserve_space_vec);