libceph: fix a osd request memory leak

If an invalid layout is provided to ceph_osdc_new_request(), its
call to calc_layout() might return an error.  At that point in the
function we've already allocated an osd request structure, so we
need to free it (drop a reference) in the event such an error
occurs.

The only other value calc_layout() will return is 0, so make that
explicit in the successful case.

This resolves:
    http://tracker.ceph.com/issues/4240

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

net/ceph/osd_client.c

@@ -109,7 +109,7 @@ static int calc_layout(struct ceph_vino vino,
 	snprintf(req->r_oid, sizeof(req->r_oid), "%llx.%08llx", vino.ino, bno);
 	req->r_oid_len = strlen(req->r_oid);
 
-	return r;
+	return 0;
 }
 
 /*
@@ -470,8 +470,10 @@ struct ceph_osd_request *ceph_osdc_new_request(struct ceph_osd_client *osdc,
 
 	/* calculate max write size */
 	r = calc_layout(vino, layout, off, plen, req, ops);
-	if (r < 0)
+	if (r < 0) {
+		ceph_osdc_put_request(req);
 		return ERR_PTR(r);
+	}
 	req->r_file_layout = *layout;  /* keep a copy */
 
 	/* in case it differs from natural (file) alignment that