mon: Monitor: 'ceph df'

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
client: root can write to any file

Signed-off-by: Sage Weil <sage@inktank.com>
client: handle fh cleanup in ll_create() failure path

Release the gh if we fail the permissions check.

Signed-off-by: Sage Weil <sage@inktank.com>
mds: do not do traceless reply for open O_TRUNC requests

Even though these are "may_write" and may be a mutation, the MDS should not
fake out a traceless reply.  In a real failure, it looks like:

 - mds process request (mutation)
 - mds fails
 - client resends request
 - mds notes that it is O_TRUNC, and already committed, and proceeds with
   a regular open

And that is all fine.

But, that means that if we are trying to simulate this behavior without a
failure, then we should never do a traceless reply on an O_TRUNC request,
because the client will never see such a reply--it'll get a full open
request response instead.

Signed-off-by: Sage Weil <sage@inktank.com>