libceph: handle zero-length data items

rbd needs this for null copyups -- if copyup data is all zeroes, we
want to save some I/O and network bandwidth.  See rbd_obj_issue_copyup()
in the next commit.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 91a5785..cee4b3d 100644 (file)
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -1605,13 +1605,18 @@ static int write_partial_message_data(struct ceph_connection *con)
         * been revoked, so use the zero page.
         */
        crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
-       while (cursor->resid) {
+       while (cursor->total_resid) {
                struct page *page;
                size_t page_offset;
                size_t length;
                bool last_piece;
                int ret;
 
+               if (!cursor->resid) {
+                       ceph_msg_data_advance(cursor, 0);
+                       continue;
+               }
+
                page = ceph_msg_data_next(cursor, &page_offset, &length,
                                          &last_piece);
                ret = ceph_tcp_sendpage(con->sock, page, page_offset,
@@ -2327,7 +2332,12 @@ static int read_partial_msg_data(struct ceph_connection *con)
 
        if (do_datacrc)
                crc = con->in_data_crc;
-       while (cursor->resid) {
+       while (cursor->total_resid) {
+               if (!cursor->resid) {
+                       ceph_msg_data_advance(cursor, 0);
+                       continue;
+               }
+
                page = ceph_msg_data_next(cursor, &page_offset, &length, NULL);
                ret = ceph_tcp_recvpage(con->sock, page, page_offset, length);
                if (ret <= 0) {