libceph: use data cursor for message pagelist
Switch to using the message cursor for the (non-trail) outgoing
pagelist data item in a message if present.
Notes on the logic changes in out_msg_pos_next():
- only the mds client uses a ceph pagelist for message data;
- if the mds client ever uses a pagelist, it never uses a page
array (or anything else, for that matter) for data in the same
message;
- only the osd client uses the trail portion of a message data,
and when it does, it never uses any other data fields for
outgoing data in the same message; and finally
- only the rbd client uses bio message data (never pagelist).
Therefore out_msg_pos_next() can assume:
- if we're in the trail portion of a message, the message data
pagelist, data, and bio can be ignored; and
- if there is a page list, there will never be any a bio or page
array data, and vice-versa.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
1 file changed