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>

1 files changed, 12 insertions, 2 deletions

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 91a57857cf11..cee4b3d307de 100644
--- 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          * been revoked, so use the zero page.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) {