libceph: make message data be a pointer

Begin the transition from a single message data item to a list of
them by replacing the "data" structure in a message with a pointer
to a ceph_msg_data structure.

A null pointer will indicate the message has no data; replace the
use of ceph_msg_has_data() with a simple check for a null pointer.

Create functions ceph_msg_data_create() and ceph_msg_data_destroy()
to dynamically allocate and free a data item structure of a given type.

When a message has its data item "set," allocate one of these to
hold the data description, and free it when the last reference to
the message is dropped.

This partially resolves:
    http://tracker.ceph.com/issues/4429Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/messenger.h

@@ -64,8 +64,6 @@ struct ceph_messenger {
 	u32 required_features;
 };
 
-#define ceph_msg_has_data(m)		((m)->data.type != CEPH_MSG_DATA_NONE)
-
 enum ceph_msg_data_type {
 	CEPH_MSG_DATA_NONE,	/* message contains no data payload */
 	CEPH_MSG_DATA_PAGES,	/* data source/destination is a page array */
@@ -141,8 +139,7 @@ struct ceph_msg {
 	struct kvec front;              /* unaligned blobs of message */
 	struct ceph_buffer *middle;
 
-	/* data payload */
-	struct ceph_msg_data	data;
+	struct ceph_msg_data	*data;	/* data payload */
 
 	struct ceph_connection *con;
 	struct list_head list_head;	/* links for connection lists */

net/ceph/messenger.c

@@ -1086,7 +1086,7 @@ static void prepare_message_data(struct ceph_msg *msg)
 
 	/* Initialize data cursor */
 
-	ceph_msg_data_cursor_init(&msg->data, data_len);
+	ceph_msg_data_cursor_init(msg->data, data_len);
 }
 
 /*
@@ -1406,13 +1406,13 @@ static u32 ceph_crc32c_page(u32 crc, struct page *page,
 static int write_partial_message_data(struct ceph_connection *con)
 {
 	struct ceph_msg *msg = con->out_msg;
-	struct ceph_msg_data_cursor *cursor = &msg->data.cursor;
+	struct ceph_msg_data_cursor *cursor = &msg->data->cursor;
 	bool do_datacrc = !con->msgr->nocrc;
 	u32 crc;
 
 	dout("%s %p msg %p\n", __func__, con, msg);
 
-	if (WARN_ON(!ceph_msg_has_data(msg)))
+	if (WARN_ON(!msg->data))
 		return -EINVAL;
 
 	/*
@@ -1432,7 +1432,7 @@ static int write_partial_message_data(struct ceph_connection *con)
 		bool need_crc;
 		int ret;
 
-		page = ceph_msg_data_next(&msg->data, &page_offset, &length,
+		page = ceph_msg_data_next(msg->data, &page_offset, &length,
 							&last_piece);
 		ret = ceph_tcp_sendpage(con->sock, page, page_offset,
 				      length, last_piece);
@@ -1444,7 +1444,7 @@ static int write_partial_message_data(struct ceph_connection *con)
 		}
 		if (do_datacrc && cursor->need_crc)
 			crc = ceph_crc32c_page(crc, page, page_offset, length);
-		need_crc = ceph_msg_data_advance(&msg->data, (size_t) ret);
+		need_crc = ceph_msg_data_advance(msg->data, (size_t)ret);
 	}
 
 	dout("%s %p msg %p done\n", __func__, con, msg);
@@ -2104,7 +2104,7 @@ static int read_partial_message_section(struct ceph_connection *con,
 static int read_partial_msg_data(struct ceph_connection *con)
 {
 	struct ceph_msg *msg = con->in_msg;
-	struct ceph_msg_data_cursor *cursor = &msg->data.cursor;
+	struct ceph_msg_data_cursor *cursor = &msg->data->cursor;
 	const bool do_datacrc = !con->msgr->nocrc;
 	struct page *page;
 	size_t page_offset;
@@ -2113,13 +2113,13 @@ static int read_partial_msg_data(struct ceph_connection *con)
 	int ret;
 
 	BUG_ON(!msg);
-	if (WARN_ON(!ceph_msg_has_data(msg)))
+	if (!msg->data)
 		return -EIO;
 
 	if (do_datacrc)
 		crc = con->in_data_crc;
 	while (cursor->resid) {
-		page = ceph_msg_data_next(&msg->data, &page_offset, &length,
+		page = ceph_msg_data_next(msg->data, &page_offset, &length,
 							NULL);
 		ret = ceph_tcp_recvpage(con->sock, page, page_offset, length);
 		if (ret <= 0) {
@@ -2131,7 +2131,7 @@ static int read_partial_msg_data(struct ceph_connection *con)
 
 		if (do_datacrc)
 			crc = ceph_crc32c_page(crc, page, page_offset, ret);
-		(void) ceph_msg_data_advance(&msg->data, (size_t) ret);
+		(void) ceph_msg_data_advance(msg->data, (size_t)ret);
 	}
 	if (do_datacrc)
 		con->in_data_crc = crc;
@@ -2947,44 +2947,80 @@ void ceph_con_keepalive(struct ceph_connection *con)
 }
 EXPORT_SYMBOL(ceph_con_keepalive);
 
-static void ceph_msg_data_init(struct ceph_msg_data *data)
+static struct ceph_msg_data *ceph_msg_data_create(enum ceph_msg_data_type type)
 {
-	data->type = CEPH_MSG_DATA_NONE;
+	struct ceph_msg_data *data;
+
+	if (WARN_ON(!ceph_msg_data_type_valid(type)))
+		return NULL;
+
+	data = kzalloc(sizeof (*data), GFP_NOFS);
+	if (data)
+		data->type = type;
+
+	return data;
+}
+
+static void ceph_msg_data_destroy(struct ceph_msg_data *data)
+{
+	if (!data)
+		return;
+
+	if (data->type == CEPH_MSG_DATA_PAGELIST) {
+		ceph_pagelist_release(data->pagelist);
+		kfree(data->pagelist);
+	}
+	kfree(data);
 }
 
 void ceph_msg_data_set_pages(struct ceph_msg *msg, struct page **pages,
 		size_t length, size_t alignment)
 {
+	struct ceph_msg_data *data;
+
 	BUG_ON(!pages);
 	BUG_ON(!length);
-	BUG_ON(msg->data.type != CEPH_MSG_DATA_NONE);
+	BUG_ON(msg->data != NULL);
+
+	data = ceph_msg_data_create(CEPH_MSG_DATA_PAGES);
+	BUG_ON(!data);
+	data->pages = pages;
+	data->length = length;
+	data->alignment = alignment & ~PAGE_MASK;
 
-	msg->data.type = CEPH_MSG_DATA_PAGES;
-	msg->data.pages = pages;
-	msg->data.length = length;
-	msg->data.alignment = alignment & ~PAGE_MASK;
+	msg->data = data;
 }
 EXPORT_SYMBOL(ceph_msg_data_set_pages);
 
 void ceph_msg_data_set_pagelist(struct ceph_msg *msg,
 				struct ceph_pagelist *pagelist)
 {
+	struct ceph_msg_data *data;
+
 	BUG_ON(!pagelist);
 	BUG_ON(!pagelist->length);
-	BUG_ON(msg->data.type != CEPH_MSG_DATA_NONE);
+	BUG_ON(msg->data != NULL);
 
-	msg->data.type = CEPH_MSG_DATA_PAGELIST;
-	msg->data.pagelist = pagelist;
+	data = ceph_msg_data_create(CEPH_MSG_DATA_PAGELIST);
+	BUG_ON(!data);
+	data->pagelist = pagelist;
+
+	msg->data = data;
 }
 EXPORT_SYMBOL(ceph_msg_data_set_pagelist);
 
 void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio)
 {
+	struct ceph_msg_data *data;
+
 	BUG_ON(!bio);
-	BUG_ON(msg->data.type != CEPH_MSG_DATA_NONE);
+	BUG_ON(msg->data != NULL);
 
-	msg->data.type = CEPH_MSG_DATA_BIO;
-	msg->data.bio = bio;
+	data = ceph_msg_data_create(CEPH_MSG_DATA_BIO);
+	BUG_ON(!data);
+	data->bio = bio;
+
+	msg->data = data;
 }
 EXPORT_SYMBOL(ceph_msg_data_set_bio);
 
@@ -3008,8 +3044,6 @@ struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 	INIT_LIST_HEAD(&m->list_head);
 	kref_init(&m->kref);
 
-	ceph_msg_data_init(&m->data);
-
 	/* front */
 	m->front_max = front_len;
 	if (front_len) {
@@ -3163,14 +3197,8 @@ void ceph_msg_last_put(struct kref *kref)
 		ceph_buffer_put(m->middle);
 		m->middle = NULL;
 	}
-	if (ceph_msg_has_data(m)) {
-		if (m->data.type == CEPH_MSG_DATA_PAGELIST) {
-			ceph_pagelist_release(m->data.pagelist);
-			kfree(m->data.pagelist);
-		}
-		memset(&m->data, 0, sizeof m->data);
-		ceph_msg_data_init(&m->data);
-	}
+	ceph_msg_data_destroy(m->data);
+	m->data = NULL;
 
 	if (m->pool)
 		ceph_msgpool_put(m->pool, m);
@@ -3182,7 +3210,7 @@ EXPORT_SYMBOL(ceph_msg_last_put);
 void ceph_msg_dump(struct ceph_msg *msg)
 {
 	pr_debug("msg_dump %p (front_max %d length %zd)\n", msg,
-		 msg->front_max, msg->data.length);
+		 msg->front_max, msg->data->length);
 	print_hex_dump(KERN_DEBUG, "header: ",
 		       DUMP_PREFIX_OFFSET, 16, 1,
 		       &msg->hdr, sizeof(msg->hdr), true);