Ceph » rbd

While getting copyup functionality working I found two
bugs in the messenger that previously were not triggered.

- In ceph_msg_data_pagelist_cursor_init(), the cursor's
last_piece field was being checked against the length
supplied. This was OK until this commit:
ccba6d98 libceph: implement multiple data items in a message
That commit changed the cursor init routines to allow
lengths to be supplied that exceeded the size of the
current data item. Because of this, we have to use
the assigned cursor resid field rather than the provided
length in determining whether the cursor points to the
last piece of a data item.
- In ceph_msg_data_add_pages(), a BUG_ON() was erroneously
catching attempts to add page data to a message if the
message already had data assigned to it. That was OK
until that same commit, at which point it was fine for
messages to have multiple data items. It slipped through
because that BUG_ON() call was present twice in that
function. (You can never be too careful.)

In addition there are two other minor changes:
- In ceph_msg_data_cursor_init(), the local variable "data"
was getting assigned twice.
- In ceph_msg_data_advance(), it was assumed that the
type-specific advance routine would set new_piece to true
after it advanced past the last piece. That may have been
fine, but since we check for that case we might as well
set it explicitly in ceph_msg_data_advance().