Ceph » Linux kernel client

While looking at http://tracker.ceph.com/issues/3875 I learned
that the nr_pages field in a ceph message is never really used
to validate anything, it's just used for debug messages.

Validating would be a good thing to do though. However, for
a bio-based request, "nr_pages" isn't really meaningful, but
the total number of bytes in the request would be and would
make sense for a page-based request as well.

There is a data_len field in a ceph_msg_header structure, and
that may well be the same as what I'm suggesting. And in that
case it would be better to just use that rather than create a
redundant field.

(I was on the verge of simply doing this, but tracking down
how precisely the data_len field in a header got to be too
much.)