libceph: prepare for other message data item types

This just inserts some infrastructure in preparation for handling
other types of ceph message data items.  No functional changes,
just trying to simplify review by separating out some noise.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/messenger.h

@@ -97,8 +97,12 @@ static __inline__ bool ceph_msg_data_type_valid(enum ceph_msg_data_type type)
 
 struct ceph_msg_data_cursor {
 	bool		last_piece;	/* now at last piece of data item */
-	struct page	*page;		/* current page in pagelist */
-	size_t		offset;		/* pagelist bytes consumed */
+	union {
+		struct {				/* pagelist */
+			struct page	*page;		/* page from list */
+			size_t		offset;		/* bytes from list */
+		};
+	};
 };
 
 struct ceph_msg_data {

net/ceph/messenger.c

@@ -742,21 +742,16 @@ static void iter_bio_next(struct bio **bio_iter, unsigned int *seg)
 #endif
 
 /*
- * Message data is handled (sent or received) in pieces, where each
- * piece resides on a single page.  The network layer might not
- * consume an entire piece at once.  A data item's cursor keeps
- * track of which piece is next to process and how much remains to
- * be processed in that piece.  It also tracks whether the current
- * piece is the last one in the data item.
+ * For a pagelist, a piece is whatever remains to be consumed in the
+ * first page in the list, or the front of the next page.
  */
-static void ceph_msg_data_cursor_init(struct ceph_msg_data *data)
+static void ceph_msg_data_pagelist_cursor_init(struct ceph_msg_data *data)
 {
 	struct ceph_msg_data_cursor *cursor = &data->cursor;
 	struct ceph_pagelist *pagelist;
 	struct page *page;
 
-	if (data->type != CEPH_MSG_DATA_PAGELIST)
-		return;
+	BUG_ON(data->type != CEPH_MSG_DATA_PAGELIST);
 
 	pagelist = data->pagelist;
 	BUG_ON(!pagelist);
@@ -771,15 +766,9 @@ static void ceph_msg_data_cursor_init(struct ceph_msg_data *data)
 	cursor->last_piece = pagelist->length <= PAGE_SIZE;
 }
 
-/*
- * Return the page containing the next piece to process for a given
- * data item, and supply the page offset and length of that piece.
- * Indicate whether this is the last piece in this data item.
- */
-static struct page *ceph_msg_data_next(struct ceph_msg_data *data,
+static struct page *ceph_msg_data_pagelist_next(struct ceph_msg_data *data,
 						size_t *page_offset,
-						size_t *length,
-						bool *last_piece)
+						size_t *length)
 {
 	struct ceph_msg_data_cursor *cursor = &data->cursor;
 	struct ceph_pagelist *pagelist;
@@ -793,8 +782,7 @@ static struct page *ceph_msg_data_next(struct ceph_msg_data *data,
 	BUG_ON(!cursor->page);
 	BUG_ON(cursor->offset >= pagelist->length);
 
-	*last_piece = cursor->last_piece;
-	if (*last_piece) {
+	if (cursor->last_piece) {
 		/* pagelist offset is always 0 */
 		piece_end = pagelist->length & ~PAGE_MASK;
 		if (!piece_end)
@@ -808,11 +796,8 @@ static struct page *ceph_msg_data_next(struct ceph_msg_data *data,
 	return data->cursor.page;
 }
 
-/*
- * Returns true if the result moves the cursor on to the next piece
- * (the next page) of the pagelist.
- */
-static bool ceph_msg_data_advance(struct ceph_msg_data *data, size_t bytes)
+static bool ceph_msg_data_pagelist_advance(struct ceph_msg_data *data,
+						size_t bytes)
 {
 	struct ceph_msg_data_cursor *cursor = &data->cursor;
 	struct ceph_pagelist *pagelist;
@@ -844,6 +829,90 @@ static bool ceph_msg_data_advance(struct ceph_msg_data *data, size_t bytes)
 	return true;
 }
 
+/*
+ * Message data is handled (sent or received) in pieces, where each
+ * piece resides on a single page.  The network layer might not
+ * consume an entire piece at once.  A data item's cursor keeps
+ * track of which piece is next to process and how much remains to
+ * be processed in that piece.  It also tracks whether the current
+ * piece is the last one in the data item.
+ */
+static void ceph_msg_data_cursor_init(struct ceph_msg_data *data)
+{
+	switch (data->type) {
+	case CEPH_MSG_DATA_PAGELIST:
+		ceph_msg_data_pagelist_cursor_init(data);
+		break;
+	case CEPH_MSG_DATA_NONE:
+	case CEPH_MSG_DATA_PAGES:
+#ifdef CONFIG_BLOCK
+	case CEPH_MSG_DATA_BIO:
+#endif /* CONFIG_BLOCK */
+	default:
+		/* BUG(); */
+		break;
+	}
+}
+
+/*
+ * Return the page containing the next piece to process for a given
+ * data item, and supply the page offset and length of that piece.
+ * Indicate whether this is the last piece in this data item.
+ */
+static struct page *ceph_msg_data_next(struct ceph_msg_data *data,
+					size_t *page_offset,
+					size_t *length,
+					bool *last_piece)
+{
+	struct page *page;
+
+	switch (data->type) {
+	case CEPH_MSG_DATA_PAGELIST:
+		page = ceph_msg_data_pagelist_next(data, page_offset, length);
+		break;
+	case CEPH_MSG_DATA_NONE:
+	case CEPH_MSG_DATA_PAGES:
+#ifdef CONFIG_BLOCK
+	case CEPH_MSG_DATA_BIO:
+#endif /* CONFIG_BLOCK */
+	default:
+		page = NULL;
+		break;
+	}
+	BUG_ON(!page);
+	BUG_ON(*page_offset + *length > PAGE_SIZE);
+	BUG_ON(!*length);
+	if (last_piece)
+		*last_piece = data->cursor.last_piece;
+
+	return page;
+}
+
+/*
+ * Returns true if the result moves the cursor on to the next piece
+ * of the data item.
+ */
+static bool ceph_msg_data_advance(struct ceph_msg_data *data, size_t bytes)
+{
+	bool new_piece;
+
+	switch (data->type) {
+	case CEPH_MSG_DATA_PAGELIST:
+		new_piece = ceph_msg_data_pagelist_advance(data, bytes);
+		break;
+	case CEPH_MSG_DATA_NONE:
+	case CEPH_MSG_DATA_PAGES:
+#ifdef CONFIG_BLOCK
+	case CEPH_MSG_DATA_BIO:
+#endif /* CONFIG_BLOCK */
+	default:
+		BUG();
+		break;
+	}
+
+	return new_piece;
+}
+
 static void prepare_message_data(struct ceph_msg *msg,
 				struct ceph_msg_pos *msg_pos)
 {