SUNRPC: Refactor svc_recvfrom()

This function is not currently "generic" so remove the documenting
comment and rename it appropriately. Its internals are converted to
use bio_vecs for reading from the transport socket.

In existing typical sunrpc uses of bio_vecs, the bio_vec array is
allocated dynamically. Here, instead, an array of bio_vecs is added
to svc_rqst. The lifetime of this array can be greater than one call
to xpo_recvfrom():

- Multiple calls to xpo_recvfrom() might be needed to read an RPC
  message completely.

- At some later point, rq_arg.bvecs will point to this array and it
  will carry the received message into svc_process().

I also expect that a future optimization will remove either the
rq_vec or rq_pages array in favor of rq_bvec, thus conserving the
size of struct svc_rqst.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc.h

@@ -254,6 +254,7 @@ struct svc_rqst {
 	struct page *		*rq_page_end;  /* one past the last page */
 
 	struct kvec		rq_vec[RPCSVC_MAXPAGES]; /* generally useful.. */
+	struct bio_vec		rq_bvec[RPCSVC_MAXPAGES];
 
 	__be32			rq_xid;		/* transmission id */
 	u32			rq_prog;	/* program number */

net/sunrpc/svcsock.c

@@ -223,26 +223,62 @@ static int svc_one_sock_name(struct svc_sock *svsk, char *buf, int remaining)
 	return len;
 }
 
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+static void svc_flush_bvec(const struct bio_vec *bvec, size_t size, size_t seek)
+{
+	struct bvec_iter bi = {
+		.bi_size	= size,
+	};
+	struct bio_vec bv;
+
+	bvec_iter_advance(bvec, &bi, seek & PAGE_MASK);
+	for_each_bvec(bv, bvec, bi, bi)
+		flush_dcache_page(bv.bv_page);
+}
+#else
+static inline void svc_flush_bvec(const struct bio_vec *bvec, size_t size,
+				  size_t seek)
+{
+}
+#endif
+
 /*
- * Generic recvfrom routine.
+ * Read from @rqstp's transport socket. The incoming message fills whole
+ * pages in @rqstp's rq_pages array until the last page of the message
+ * has been received into a partial page.
  */
-static ssize_t svc_recvfrom(struct svc_rqst *rqstp, struct kvec *iov,
-			    unsigned int nr, size_t buflen, unsigned int base)
+static ssize_t svc_tcp_read_msg(struct svc_rqst *rqstp, size_t buflen,
+				size_t seek)
 {
 	struct svc_sock *svsk =
 		container_of(rqstp->rq_xprt, struct svc_sock, sk_xprt);
+	struct bio_vec *bvec = rqstp->rq_bvec;
 	struct msghdr msg = { NULL };
+	unsigned int i;
 	ssize_t len;
+	size_t t;
 
 	rqstp->rq_xprt_hlen = 0;
 
 	clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
-	iov_iter_kvec(&msg.msg_iter, READ, iov, nr, buflen);
-	if (base != 0) {
-		iov_iter_advance(&msg.msg_iter, base);
-		buflen -= base;
+
+	for (i = 0, t = 0; t < buflen; i++, t += PAGE_SIZE) {
+		bvec[i].bv_page = rqstp->rq_pages[i];
+		bvec[i].bv_len = PAGE_SIZE;
+		bvec[i].bv_offset = 0;
+	}
+	rqstp->rq_respages = &rqstp->rq_pages[i];
+	rqstp->rq_next_page = rqstp->rq_respages + 1;
+
+	iov_iter_bvec(&msg.msg_iter, READ, bvec, i, buflen);
+	if (seek) {
+		iov_iter_advance(&msg.msg_iter, seek);
+		buflen -= seek;
 	}
 	len = sock_recvmsg(svsk->sk_sock, &msg, MSG_DONTWAIT);
+	if (len > 0)
+		svc_flush_bvec(bvec, len, seek);
+
 	/* If we read a full record, then assume there may be more
 	 * data to read (stream based sockets only!)
 	 */
@@ -775,13 +811,14 @@ static struct svc_xprt *svc_tcp_accept(struct svc_xprt *xprt)
 	return NULL;
 }
 
-static unsigned int svc_tcp_restore_pages(struct svc_sock *svsk, struct svc_rqst *rqstp)
+static size_t svc_tcp_restore_pages(struct svc_sock *svsk,
+				    struct svc_rqst *rqstp)
 {
-	unsigned int i, len, npages;
+	size_t len = svsk->sk_datalen;
+	unsigned int i, npages;
 
-	if (svsk->sk_datalen == 0)
+	if (!len)
 		return 0;
-	len = svsk->sk_datalen;
 	npages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	for (i = 0; i < npages; i++) {
 		if (rqstp->rq_pages[i] != NULL)
@@ -917,20 +954,6 @@ static int receive_cb_reply(struct svc_sock *svsk, struct svc_rqst *rqstp)
 	return -EAGAIN;
 }
 
-static int copy_pages_to_kvecs(struct kvec *vec, struct page **pages, int len)
-{
-	int i = 0;
-	int t = 0;
-
-	while (t < len) {
-		vec[i].iov_base = page_address(pages[i]);
-		vec[i].iov_len = PAGE_SIZE;
-		i++;
-		t += PAGE_SIZE;
-	}
-	return i;
-}
-
 static void svc_tcp_fragment_received(struct svc_sock *svsk)
 {
 	/* If we have more data, signal svc_xprt_enqueue() to try again */
@@ -938,20 +961,33 @@ static void svc_tcp_fragment_received(struct svc_sock *svsk)
 	svsk->sk_marker = xdr_zero;
 }
 
-/*
- * Receive data from a TCP socket.
+/**
+ * svc_tcp_recvfrom - Receive data from a TCP socket
+ * @rqstp: request structure into which to receive an RPC Call
+ *
+ * Called in a loop when XPT_DATA has been set.
+ *
+ * Read the 4-byte stream record marker, then use the record length
+ * in that marker to set up exactly the resources needed to receive
+ * the next RPC message into @rqstp.
+ *
+ * Returns:
+ *   On success, the number of bytes in a received RPC Call, or
+ *   %0 if a complete RPC Call message was not ready to return
+ *
+ * The zero return case handles partial receives and callback Replies.
+ * The state of a partial receive is preserved in the svc_sock for
+ * the next call to svc_tcp_recvfrom.
  */
 static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 {
 	struct svc_sock	*svsk =
 		container_of(rqstp->rq_xprt, struct svc_sock, sk_xprt);
 	struct svc_serv	*serv = svsk->sk_xprt.xpt_server;
-	int		len;
-	struct kvec *vec;
-	unsigned int want, base;
+	size_t want, base;
+	ssize_t len;
 	__be32 *p;
 	__be32 calldir;
-	int pnum;
 
 	clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
 	len = svc_tcp_read_marker(svsk, rqstp);
@@ -960,16 +996,7 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 
 	base = svc_tcp_restore_pages(svsk, rqstp);
 	want = len - (svsk->sk_tcplen - sizeof(rpc_fraghdr));
-
-	vec = rqstp->rq_vec;
-
-	pnum = copy_pages_to_kvecs(&vec[0], &rqstp->rq_pages[0], base + want);
-
-	rqstp->rq_respages = &rqstp->rq_pages[pnum];
-	rqstp->rq_next_page = rqstp->rq_respages + 1;
-
-	/* Now receive data */
-	len = svc_recvfrom(rqstp, vec, pnum, base + want, base);
+	len = svc_tcp_read_msg(rqstp, base + want, base);
 	if (len >= 0) {
 		trace_svcsock_tcp_recv(&svsk->sk_xprt, len);
 		svsk->sk_tcplen += len;