afs: Use a bvec rather than a kvec in afs_send_pages()

Use a bvec rather than a kvec in afs_send_pages() as we don't then have to
call kmap() in advance.  This allows us to pass the array of contiguous
pages that we extracted through to rxrpc in one go rather than passing a
single page at a time.
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/rxrpc.c

@@ -259,67 +259,74 @@ void afs_flat_call_destructor(struct afs_call *call)
 	call->buffer = NULL;
 }
 
+#define AFS_BVEC_MAX 8
+
+/*
+ * Load the given bvec with the next few pages.
+ */
+static void afs_load_bvec(struct afs_call *call, struct msghdr *msg,
+			  struct bio_vec *bv, pgoff_t first, pgoff_t last,
+			  unsigned offset)
+{
+	struct page *pages[AFS_BVEC_MAX];
+	unsigned int nr, n, i, to, bytes = 0;
+
+	nr = min_t(pgoff_t, last - first + 1, AFS_BVEC_MAX);
+	n = find_get_pages_contig(call->mapping, first, nr, pages);
+	ASSERTCMP(n, ==, nr);
+
+	msg->msg_flags |= MSG_MORE;
+	for (i = 0; i < nr; i++) {
+		to = PAGE_SIZE;
+		if (first + i >= last) {
+			to = call->last_to;
+			msg->msg_flags &= ~MSG_MORE;
+		}
+		bv[i].bv_page = pages[i];
+		bv[i].bv_len = to - offset;
+		bv[i].bv_offset = offset;
+		bytes += to - offset;
+		offset = 0;
+	}
+
+	iov_iter_bvec(&msg->msg_iter, WRITE | ITER_BVEC, bv, nr, bytes);
+}
+
 /*
  * attach the data from a bunch of pages on an inode to a call
  */
 static int afs_send_pages(struct afs_call *call, struct msghdr *msg)
 {
-	struct page *pages[8];
-	unsigned count, n, loop, offset, to;
+	struct bio_vec bv[AFS_BVEC_MAX];
+	unsigned int bytes, nr, loop, offset;
 	pgoff_t first = call->first, last = call->last;
 	int ret;
 
-	_enter("");
-
 	offset = call->first_offset;
 	call->first_offset = 0;
 
 	do {
-		_debug("attach %lx-%lx", first, last);
-
-		count = last - first + 1;
-		if (count > ARRAY_SIZE(pages))
-			count = ARRAY_SIZE(pages);
-		n = find_get_pages_contig(call->mapping, first, count, pages);
-		ASSERTCMP(n, ==, count);
-
-		loop = 0;
-		do {
-			struct bio_vec bvec = {.bv_page = pages[loop],
-					       .bv_offset = offset};
-			msg->msg_flags = 0;
-			to = PAGE_SIZE;
-			if (first + loop >= last)
-				to = call->last_to;
-			else
-				msg->msg_flags = MSG_MORE;
-			bvec.bv_len = to - offset;
+		afs_load_bvec(call, msg, bv, first, last, offset);
 		offset = 0;
+		bytes = msg->msg_iter.count;
+		nr = msg->msg_iter.nr_segs;
 
-			_debug("- range %u-%u%s",
-			       offset, to, msg->msg_flags ? " [more]" : "");
-			iov_iter_bvec(&msg->msg_iter, WRITE | ITER_BVEC,
-				      &bvec, 1, to - offset);
-
-			/* have to change the state *before* sending the last
+		/* Have to change the state *before* sending the last
 		 * packet as RxRPC might give us the reply before it
-			 * returns from sending the request */
-			if (first + loop >= last)
+		 * returns from sending the request.
+		 */
+		if (first + nr >= last)
 			call->state = AFS_CALL_AWAIT_REPLY;
 		ret = rxrpc_kernel_send_data(afs_socket, call->rxcall,
-						     msg, to - offset);
+					     msg, bytes);
+		for (loop = 0; loop < nr; loop++)
+			put_page(bv[loop].bv_page);
 		if (ret < 0)
 			break;
-		} while (++loop < count);
-		first += count;
 
-		for (loop = 0; loop < count; loop++)
-			put_page(pages[loop]);
-		if (ret < 0)
-			break;
+		first += nr;
 	} while (first <= last);
 
-	_leave(" = %d", ret);
 	return ret;
 }